is the life on other planets essay

Scientific researchers on a bat-collecting expedition in Sierra Leone. Photo by Simon Townley/Panos

There’s no planet B

The scientific evidence is clear: the only celestial body that can support us is the one we evolved with. here’s why.

by Arwen E Nicholson & Raphaëlle D Haywood   + BIO

At the start of the 22nd century, humanity left Earth for the stars. The enormous ecological and climatic devastation that had characterised the last 100 years had led to a world barren and inhospitable; we had used up Earth entirely. Rapid melting of ice caused the seas to rise, swallowing cities whole. Deforestation ravaged forests around the globe, causing widespread destruction and loss of life. All the while, we continued to burn the fossil fuels we knew to be poisoning us, and thus created a world no longer fit for our survival. And so we set our sights beyond Earth’s horizons to a new world, a place to begin again on a planet as yet untouched. But where are we going? What are our chances of finding the elusive planet B, an Earth-like world ready and waiting to welcome and shelter humanity from the chaos we created on the planet that brought us into being? We built powerful astronomical telescopes to search the skies for planets resembling our own, and very quickly found hundreds of Earth twins orbiting distant stars. Our home was not so unique after all. The universe is full of Earths!

This futuristic dream-like scenario is being sold to us as a real scientific possibility, with billionaires planning to move humanity to Mars in the near future. For decades, children have grown up with the daring movie adventures of intergalactic explorers and the untold habitable worlds they find. Many of the highest-grossing films are set on fictional planets, with paid advisors keeping the science ‘realistic’. At the same time, narratives of humans trying to survive on a post-apocalyptic Earth have also become mainstream.

Given all our technological advances, it’s tempting to believe we are approaching an age of interplanetary colonisation. But can we really leave Earth and all our worries behind? No. All these stories are missing what makes a planet habitable to us . What Earth-like means in astronomy textbooks and what it means to someone considering their survival prospects on a distant world are two vastly different things. We don’t just need a planet roughly the same size and temperature as Earth; we need a planet that spent billions of years evolving with us. We depend completely on the billions of other living organisms that make up Earth’s biosphere. Without them, we cannot survive. Astronomical observations and Earth’s geological record are clear: the only planet that can support us is the one we evolved with. There is no plan B. There is no planet B. Our future is here, and it doesn’t have to mean we’re doomed.

D eep down, we know this from instinct: we are happiest when immersed in our natural environment. There are countless examples of the healing power of spending time in nature . Numerous articles speak of the benefits of ‘forest bathing’; spending time in the woods has been scientifically shown to reduce stress, anxiety and depression, and to improve sleep quality, thus nurturing both our physical and mental health. Our bodies instinctively know what we need: the thriving and unique biosphere that we have co-evolved with, that exists only here, on our home planet.

There is no planet B. These days, everyone is throwing around this catchy slogan. Most of us have seen it inscribed on an activist’s homemade placard, or heard it from a world leader. In 2014, the United Nations’ then secretary general Ban Ki-moon said: ‘There is no plan B because we do not have [a] planet B.’ The French president Emmanuel Macron echoed him in 2018 in his historical address to US Congress. There’s even a book named after it. The slogan gives strong impetus to address our planetary crisis. However, no one actually explains why there isn’t another planet we could live on, even though the evidence from Earth sciences and astronomy is clear. Gathering this observation-based information is essential to counter an increasingly popular but flawed narrative that the only way to ensure our survival is to colonise other planets.

The best-case scenario for terraforming Mars leaves us with an atmosphere we are incapable of breathing

The most common target of such speculative dreaming is our neighbour Mars. It is about half the size of Earth and receives about 40 per cent of the heat that we get from the Sun. From an astronomer’s perspective, Mars is Earth’s identical twin. And Mars has been in the news a lot lately, promoted as a possible outpost for humanity in the near future . While human-led missions to Mars seem likely in the coming decades, what are our prospects of long-term habitation on Mars? Present-day Mars is a cold, dry world with a very thin atmosphere and global dust storms that can last for weeks on end. Its average surface pressure is less than 1 per cent of Earth’s. Surviving without a pressure suit in such an environment is impossible. The dusty air mostly consists of carbon dioxide (CO 2 ) and the surface temperature ranges from a balmy 30ºC (86ºF) in the summer, down to -140ºC (-220ºF) in the winter; these extreme temperature changes are due to the thin atmosphere on Mars.

Despite these clear challenges, proposals for terraforming Mars into a world suitable for long-term human habitation abound. Mars is further from the Sun than Earth, so it would require significantly more greenhouse gases to achieve a temperature similar to Earth’s. Thickening the atmosphere by releasing CO 2 in the Martian surface is the most popular ‘solution’ to the thin atmosphere on Mars. However, every suggested method of releasing the carbon stored in Mars requires technology and resources far beyond what we are currently capable of. What’s more, a recent NASA study determined that there isn’t even enough CO 2 on Mars to warm it sufficiently.

Even if we could find enough CO 2 , we would still be left with an atmosphere we couldn’t breathe. Earth’s atmosphere contains only 0.04 per cent CO 2 , and we cannot tolerate an atmosphere high in CO 2 . For an atmosphere with Earth’s atmospheric pressure, CO 2 levels as high as 1 per cent can cause drowsiness in humans, and once we reach levels of 10 per cent CO 2 , we will suffocate even if there is abundant oxygen. The proposed absolute best-case scenario for terraforming Mars leaves us with an atmosphere we are incapable of breathing; and achieving it is well beyond our current technological and economic capabilities.

Instead of changing the atmosphere of Mars, a more realistic scenario might be to build habitat domes on its surface with internal conditions suitable for our survival. However, there would be a large pressure difference between the inside of the habitat and the outside atmosphere. Any breach in the habitat would rapidly lead to depressurisation as the breathable air escapes into the thin Martian atmosphere. Any humans living on Mars would have to be on constant high alert for any damage to their building structures, and suffocation would be a daily threat.

F rom an astronomical perspective, Mars is Earth’s twin; and yet, it would take vast resources, time and effort to transform it into a world that wouldn’t be capable of providing even the bare minimum of what we have on Earth. Suggesting that another planet could become an escape from our problems on Earth suddenly seems absurd. But are we being pessimistic? Do we just need to look further afield?

Next time you are out on a clear night, look up at the stars and choose one – you are more likely than not to pick one that hosts planets. Astronomical observations today confirm our age-old suspicion that all stars have their own planetary systems. As astronomers, we call these exoplanets. What are exoplanets like? Could we make any of them our home?

The majority of exoplanets discovered to date were found by NASA’s Kepler mission, which monitored the brightness of 100,000 stars over four years, looking for dips in a star’s light as a planet obscures it each time it completes an orbit around it.

Kepler observed more than 900 Earth-sized planets with a radius up to 1.25 times that of our world. These planets could be rocky (for the majority of them, we haven’t yet determined their mass, so we can only make this inference based on empirical relations between planetary mass and radius). Of these 900 or so Earth-sized planets, 23 are in the habitable zone. The habitable zone is the range of orbits around a star where a planet can be considered temperate : the planet’s surface can support liquid water (provided there is sufficient atmospheric pressure), a key ingredient of life as we know it. The concept of the habitable zone is very useful because it depends on just two astrophysical parameters that are relatively easy to measure: the distance of the planet to its parent star, and the star’s temperature. It’s worth keeping in mind that the astronomical habitable zone is a very simple concept and, in reality, there are many more factors at play in the emergence of life; for example, this concept does not consider plate tectonics , which are thought to be crucial to sustain life on Earth.

Planets with similar observable properties to Earth are very common: at least one in 10 stars hosts them

How many Earth-sized, temperate planets are there in our galaxy? Since we have discovered only a handful of these planets so far, it is still quite difficult to estimate their number. Current estimates of the frequency of Earth-sized planets rely on extrapolating measured occurrence rates of planets that are slightly bigger and closer to their parent star, as those are easier to detect. The studies are primarily based on observations from the Kepler mission, which surveyed more than 100,000 stars in a systematic fashion. These stars are all located in a tiny portion of the entire sky; so, occurrence rate studies assume that this part of the sky is representative of the full galaxy. These are all reasonable assumptions for the back-of-the-envelope estimate that we are about to make.

Several different teams carried out their own analyses and, on average, they found that roughly one in three stars (30 per cent) hosts an Earth-sized, temperate planet. The most pessimistic studies found a rate of 9 per cent, which is about one in 10 stars, and the studies with the most optimistic results found that virtually all stars host at least one Earth-sized, temperate planet, and potentially even several of them.

At first sight, this looks like a huge range in values; but it’s worth taking a step back and realising that we had absolutely no constraints whatsoever on this number just 20 years ago. Whether there are other planets similar to Earth is a question that we’ve been asking for millennia, and this is the very first time that we are able to answer it based on actual observations. Before the Kepler mission, we had no idea whether we would find Earth-sized, temperate planets around one in 10, or one in a million stars. Now we know that planets with similar observable properties to Earth are very common: at least one in 10 stars hosts these kinds of planets.

Let’s now use these numbers to predict the number of Earth-sized, temperate planets in our entire galaxy. For this, let’s take the average estimate of 30 per cent, or roughly one in three stars. Our galaxy hosts approximately 300 billion stars, which adds up to 90 billion roughly Earth-sized, roughly temperate planets. This is a huge number, and it can be very tempting to think that at least one of these is bound to look exactly like Earth.

One issue to consider is that other worlds are at unimaginable distances from us. Our neighbour Mars is on average 225 million kilometres (about 140 million miles) away. Imagine a team of astronauts travelling in a vehicle similar to NASA’s robotic New Horizons probe, one of humankind’s fastest spacecrafts – which flew by Pluto in 2015. With New Horizons’ top speed of around 58,000 kph, it would take at least 162 days to reach Mars. Beyond our solar system, the closest star to us is Proxima Centauri, at a distance of 40 trillion kilometres. Going in the same space vehicle, it would take our astronaut crew 79,000 years to reach planets that might exist around our nearest stellar neighbour.

S till, let’s for a moment optimistically imagine that we find a perfect Earth twin: a planet that really is exactly like Earth. Let’s imagine that some futuristic form of technology exists, ready to whisk us away to this new paradise. Keen to explore our new home, we eagerly board our rocket, but on landing we soon feel uneasy. Where is the land? Why is the ocean green and not blue? Why is the sky orange and thick with haze? Why are our instruments detecting no oxygen in the atmosphere? Was this not supposed to be a perfect twin of Earth?

As it turns out, we have landed on a perfect twin of the Archean Earth, the aeon during which life first emerged on our home world. This new planet is certainly habitable: lifeforms are floating around the green, iron-rich oceans, breathing out methane that is giving the sky that unsettling hazy, orange colour. This planet sure is habitable – just not to us . It has a thriving biosphere with plenty of life, but not life like ours. In fact, we would have been unable to survive on Earth for around 90 per cent of its history; the oxygen-rich atmosphere that we depend on is a recent feature of our planet.

The earliest part of our planet’s history, known as the Hadean aeon, begins with the formation of the Earth. Named after the Greek underworld due to our planet’s fiery beginnings, the early Hadean would have been a terrible place with molten lava oceans and an atmosphere of vaporised rock. Next came the Archean aeon, beginning 4 billion years ago, when the first life on Earth flourished. But, as we just saw, the Archean would be no home for a human. The world where our earliest ancestors thrived would kill us in an instant. After the Archean came the Proterozoic, 2.5 billion years ago. In this aeon, there was land, and a more familiar blue ocean and sky. What’s more, oxygen finally began to accumulate in the atmosphere. But let’s not get too excited: the level of oxygen was less than 10 per cent of what we have today. The air would still have been impossible for us to breathe. This time also experienced global glaciation events known as snowball Earths, where ice covered the globe from poles to equator for millions of years at a time. Earth has spent more of its time fully frozen than the length of time that we humans have existed.

We would have been incapable of living on our planet for most of its existence

Earth’s current aeon, the Phanerozoic, began only around 541 million years ago with the Cambrian explosion – a period of time when life rapidly diversified. A plethora of life including the first land plants, dinosaurs and the first flowering plants all appeared during this aeon. It is only within this aeon that our atmosphere became one that we can actually breathe. This aeon has also been characterised by multiple mass extinction events that wiped out as much as 90 per cent of all species over short periods of time. The factors that brought on such devastation are thought to be a combination of large asteroid impacts, and volcanic, chemical and climate changes occurring on Earth at the time. From the point of view of our planet, the changes leading to these mass extinctions are relatively minor. However, for lifeforms at the time, such changes shattered their world and very often led to their complete extinction.

Looking at Earth’s long history, we find that we would have been incapable of living on our planet for most of its existence. Anatomically modern humans emerged less than 400,000 years ago; we have been around for less than 0.01 per cent of the Earth’s story. The only reason we find Earth habitable now is because of the vast and diverse biosphere that has for hundreds of millions of years evolved with and shaped our planet into the home we know today. Our continued survival depends on the continuation of Earth’s present state without any nasty bumps along the way. We are complex lifeforms with complex needs. We are entirely dependent on other organisms for all our food and the very air we breathe. The collapse of Earth’s ecosystems is the collapse of our life-support systems. Replicating everything Earth offers us on another planet, on timescales of a few human lifespans, is simply impossible.

Some argue that we need to colonise other planets to ensure the future of the human race. In 5 billion years, our Sun, a middle-aged star, will become a red giant, expanding in size and possibly engulfing Earth. In 1 billion years, the gradual warming of our Sun is predicted to cause Earth’s oceans to boil away. While this certainly sounds worrying, 1 billion years is a long, long time. A billion years ago, Earth’s landmasses formed the supercontinent Rodinia, and life on Earth consisted in single-celled and small multicellular organisms. No plants or animals yet existed. The oldest Homo sapiens remains date from 315,000 years ago, and until 12,000 years ago all humans lived as hunter-gatherers.

The industrial revolution happened less than 500 years ago. Since then, human activity in burning fossil fuels has been rapidly changing the climate, threatening human lives and damaging ecosystems across the globe. Without rapid action, human-caused climate change is predicted to have devastating global consequences within the next 50 years. This is the looming crisis that humanity must focus on. If we can’t learn to work within the planetary system that we evolved with, how do we ever hope to replicate these deep processes on another planet? Considering how different human civilisations are today from even 5,000 years ago, worrying about a problem that humans may have to tackle in a billion years is simply absurd. It would be far simpler to go back in time and ask the ancient Egyptians to invent the internet there and then. It’s also worth considering that many of the attitudes towards space colonisation are worryingly close to the same exploitative attitudes that have led us to the climate crisis we now face.

Earth is the home we know and love not because it is Earth-sized and temperate. No, we call this planet our home thanks to its billion-year-old relationship with life. Just as people are shaped not only by their genetics, but by their culture and relationships with others, planets are shaped by the living organisms that emerge and thrive on them. Over time, Earth has been dramatically transformed by life into a world where we, humans, can prosper. The relationship works both ways: while life shapes its planet, the planet shapes its life. Present-day Earth is our life-support system, and we cannot live without it.

While Earth is currently our only example of a living planet, it is now within our technological reach to potentially find signs of life on other worlds. In the coming decades, we will likely answer the age-old question: are we alone in the Universe? Finding evidence for alien life promises to shake the foundations of our understanding of our own place in the cosmos. But finding alien life does not mean finding another planet that we can move to. Just as life on Earth has evolved with our planet over billions of years, forming a deep, unique relationship that makes the world we see today, any alien life on a distant planet will have a similarly deep and unique bond with its own planet. We can’t expect to be able to crash the party and find a warm welcome.

Living on a warming Earth presents many challenges. But these pale in comparison with the challenges of converting Mars, or any other planet, into a viable alternative. Scientists study Mars and other planets to better understand how Earth and life formed and evolved, and how they shape each other. We look to worlds beyond our horizons to better understand ourselves. In searching the Universe, we are not looking for an escape to our problems: Earth is our unique and only home in the cosmos. There is no planet B.

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Assistant Professor of Complex Adaptive Systems, Arizona State University

Disclosure statement

Cole Mathis has previously received funding from the NASA Postdoctoral Program.

Arizona State University provides funding as a member of The Conversation US.

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Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to [email protected] .

Why do astronomers look for signs of life on other planets based on how life is on Earth? Couldn’t there be totally different kinds of life on other planets? – Henry, age 13, Somerville, Massachusetts

Have you ever played hide-and-seek in a new place? It’s much harder than playing at home. You only know the obvious hiding spots: under the bed, in the closet, behind the couch. The trick is trying to think of hiding spots you can’t even imagine. How do you search in places you never thought could be hiding spots?

That is kind of what scientists like me do when we look for alien life; we’re trying to think of new ways to look for life. In the meantime, we’re looking for life by looking for life like us because that’s what we can imagine.

Looking nearby

The closest place to look for extraterrestrial life is on planets within our solar system.

NASA’s Viking 1 mission began orbiting Earth’s neighbor Mars back in 1976. Looking for life on Mars was one of the most important scientific questions for the mission. The spacecraft included a lander that could go to the planet’s surface to see if there were any life-forms in the dirt there.

Scientists knew that life on Mars could be really different from life on Earth, so they didn’t look for specific life-forms or molecules. Instead, they tried to design experiments to look for what life does, rather than what it makes.

For example, plants and some other life-forms on Earth do photosynthesis , a process that uses sunlight and carbon dioxide in the air to gather energy and grow. The Viking 1 scientists designed the lander to look for signs of photosynthesis happening on Mars.

To do that, the lander scooped up some dirt, shined a light on it and made measurements to see if any of the carbon dioxide in the air was transferred into the dirt. This experiment did not show any signs of photosynthesis in Mars’ dirt.

The lander had two other experiments that looked for evidence of organisms growing in the dirt on Mars. One used carbon dioxide gas and another one used sugar and amino acid molecules that life-forms on Earth like to eat.

The combination of these three experiments and other measurements led most scientists to agree that there probably is not life on the surface of Mars, at least life that does something like photosynthesis or eats sugar. But we still don’t know if there are signs of ancient life-forms on Mars, or even current life deep below the surface.

The Viking lander experiments were the most direct tests for life on other planets. In terms of a game of hide-and-seek, though, these experiments were basically like looking in the closet: It’s a pretty obvious hiding spot, but you should check there just in case. Even so, it took scientists a long time to interpret the results.

Looking far away

Looking for life outside the solar system is even harder and requires different techniques.

The closest exoplanet – a planet orbiting a star that is not our Sun – is Proxima Centauri b , and it’s more than 2 million, million miles (that’s 2 followed by 13 zeros) away from Earth. These distant worlds are so far away that scientists are not going to send landers to do experiments on them for a long time.

Looking for life on exoplanets is kind of like trying to play hide-and-seek in your neighbor’s house, but you only get to look through the windows and can’t go inside. You might get lucky and get just the right angle to spot someone hiding, but you can’t know all the spots you’re not able to see.

Tools like the new James Webb Space Telescope can reveal the size of exoplanets, how close they are to their stars, and maybe the gases in their atmospheres. But that’s it. How would you look for life with that?

Astronomers have thought about looking for life on exoplanets by looking for oxygen . They started with this strategy because on Earth, life-forms made most of the oxygen in our atmosphere. Maybe oxygen on another planet was made by alien life.

We’ve learned, though, that there are other ways to make oxygen that don’t involve life. So now, astronomers don’t look for just oxygen – instead they’re on the hunt for a planet that has oxygen along with water and other gases, like methane and carbon dioxide. Together, these combinations might indicate life because we don’t think planets without life would have them. But we’re still uncertain about that, too!

Looking for life by looking for these gases is kind of like looking behind the couch in our hide-and-seek game. Do we know anyone is going to be there? No. But we only get to look through the windows, and we can imagine people hiding behind couches. We might as well try – where else would we even look?

What game are we playing?

There are two big differences between playing hide-and-seek and looking for aliens.

First, when you’re playing hide-and-seek, you usually know that you’re playing with someone else. We have no idea if there are aliens out there to find! It’s possible there’s no other life out there, and it’s possible there are aliens right next door. Until we find examples of life besides our own, we won’t know how common life is in the universe.

The second difference is that most scientists don’t think alien life is hiding from us ; it’s just that we haven’t spotted it yet. There are some ideas that more advanced civilizations might avoid being detected , but researchers don’t think that’s happening in our solar system.

Most astronomers and astrobiologists know that if we only look for life that’s like Earth life, we might miss the signs of aliens that are really different. But honestly, we’ve never detected aliens before, so it’s hard to know where to start. When you don’t know what to do, starting somewhere is usually better than nowhere.

Looking for life using experiments like the Viking lander or searching for oxygen might not help. But we might get lucky. And even if we’re not, we’ll get to cross a couple of obvious possibilities off the list. Then we can focus on the harder question of imagining something we’ve never thought of before.

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Does life exist outside of the solar system?

Since humans first looked to the cosmos, we have wondered if life exists elsewhere in the Universe. Scientists and engineers at the Center for Astrophysics | Harvard & Smithsonian may soon be able to answer that question.

Scientists and engineers from the Center for Astrophysics aim to achieve the following advances to enable the discovery of life on other planets:

• Understand the Origins of Life: We investigate the conditions of planetary development that made life’s emergence on Earth possible.
• Modeling and Instrumentation: We develop new models for the spectroscopic signatures that identify the composition of planetary atmospheres, and build new instruments to detect them.
• Search and Observation: We identify targeted exoplanet candidates for observation, and continually refine the search process.
• Data Analysis: We use observational data to infer planetary mass, orbit, size, and composition.

How We Search

Exoplanets , or planets in solar systems other than our own, sometimes orbit directly between the Earth and their host star. When the planet orbits in front of its star, it blocks a small amount of light. CfA scientists use the Transiting Exoplanet Survey Satellite (TESS) and the Kepler space telescopes as well as the ground-based robotic telescopes of the MEarth project to look for dips in starlight. This “transit” method of planet hunting has revealed thousands of exoplanets.

During a transit, a small amount of starlight is absorbed by the planet’s atmosphere, yielding clues to the chemical makeup of the atmosphere. A massive, technologically advanced telescope is crucial for detecting the composition of an Earth-like planet’s atmosphere, including the subtle chemical signatures that life is expected to produce.

Thanks to next generation telescopes like the planned Giant Magellan Telescope (GMT) , we are approaching a point in our observational capabilities that may allow us to make previously unthinkable discoveries. One of these breakthroughs is the detection of life on a distant planet, light years away from Earth.

Juliana Garcia-Mejia working on the GMT-Consortium Large Earth Finder (G-CLEF) spectrograph for the Giant Magellan Telescope, in a lab at CfA in Cambridge, MA.

Theory of Life

Institute for Theory and Computation scientists at the CfA work on identifying the exoplanets that are most likely to harbor life. The orbit must lie in the “habitable zone” where the exoplanet’s surface is just the right temperature for liquid water to exist. Every form of life we know requires liquid water, so an exoplanet too close or too far from its host star is less likely to contain life. Additionally, ultraviolet light may be needed to form some necessary prebiotic molecules, but an overactive host star can blast the young planet, stripping away its atmosphere. When searching for extraterrestrial life, finding the perfect star could be as important as finding the perfect exoplanet.

Our Next Tool

The G-CLEF or GMT-Consortium Large Earth Finder, a next-generation spectrometer planned for use on the GMT, is our newest tool for measuring the starlight filtered through the atmosphere of an orbiting exoplanet. Using this instrument, scientists will soon be able to measure the chemical composition of a small rocky exoplanet’s atmosphere. Such an extraordinary feat is like trying to see through and study the antennae of a moth flying in front of a spotlight.

Based on our current understanding of the conditions necessary for life, the detection of biomarkers like oxygen in the atmosphere of a remote world through such observations would hint towards the presence of living organisms.

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When we look at our own planet Earth, we see life that abounds everywhere. Do these same conditions exist elsewhere in the Universe? Remarkably, 21st Century science and engineering may soon answer that question. Dr. Charles Alcock, Director, The Center for Astrophysics

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Finding life beyond earth is within reach, nasa webb telescope team.

Many scientists believe we are not alone in the universe. It’s probable, they say, that life could have arisen on at least some of the billions of planets thought to exist in our galaxy alone — just as it did here on planet Earth. This basic question about our place in the Universe is one that may be answered by scientific investigations. What are the next steps to finding life elsewhere?

Experts from NASA and its partner institutions addressed this question on July 14, at a public talk held at NASA Headquarters in Washington. They outlined NASA’s roadmap to the search for life in the universe, an ongoing journey that involves a number of current and future telescopes. Watch the video of the event:

“Sometime in the near future, people will be able to point to a star and say, ‘that star has a planet like Earth’,” says Sara Seager, professor of planetary science and physics at the Massachusetts Institute of Technology in Cambridge, Massachusetts. “Astronomers think it is very likely that every single star in our Milky Way galaxy has at least one planet.”

NASA’s quest to study planetary systems around other stars started with ground-based observatories, then moved to space-based assets like the Hubble Space Telescope , the Spitzer Space Telescope , and the Kepler Space Telescope . Today’s telescopes can look at many stars and tell if they have one or more orbiting planets. Even more, they can determine if the planets are the right distance away from the star to have liquid water, the key ingredient to life as we know it.

The NASA roadmap will continue with the launch of the Transiting Exoplanet Surveying Satellite (TESS) in 2017, the James Webb Space Telescope (Webb Telescope) in 2018, and perhaps the proposed Wide Field Infrared Survey Telescope – Astrophysics Focused Telescope Assets (WFIRST-AFTA) early in the next decade. These upcoming telescopes will find and characterize a host of new exoplanets — those planets that orbit other stars — expanding our knowledge of their atmospheres and diversity. The Webb telescope and WFIRST-AFTA will lay the groundwork, and future missions will extend the search for oceans in the form of atmospheric water vapor and for life as in carbon dioxide and other atmospheric chemicals, on nearby planets that are similar to Earth in size and mass, a key step in the search for life.

“This technology we are using to explore exoplanets is real,” said John Grunsfeld, astronaut and associate administrator for NASA’s Science Mission Directorate in Washington. “The James Webb Space Telescope and the next advances are happening now. These are not dreams — this is what we do at NASA.”

Since its launch in 2009, Kepler has dramatically changed what we know about exoplanets, finding most of the more than 5,000 potential exoplanets, of which more than 1700 have been confirmed. The Kepler observations have led to estimates of billions of planets in our galaxy, and shown that most planets within one astronomical unit are less than three times the diameter of Earth. Kepler also found the first Earth-size planet to orbit in the “habitable zone” of a star, the region where liquid water can pool on the surface.

“What we didn’t know five years ago is that perhaps 10 to 20 percent of stars around us have Earth-size planets in the habitable zone,” says Matt Mountain, director and Webb telescope scientist at the Space Telescope Science Institute in Baltimore. “It’s within our grasp to pull off a discovery that will change the world forever. It is going to take a continuing partnership between NASA, science, technology, the U.S. and international space endeavors, as exemplified by the James Webb Space Telescope, to build the next bridge to humanity’s future.”

This decade has seen the discovery of more and more super Earths, which are rocky planets that are larger and heftier than Earth. Finding smaller planets, the Earth twins, is a tougher challenge because they produce fainter signals. Technology to detect and image these Earth-like planets is being developed now for use with the future space telescopes. The ability to detect alien life may still be years or more away, but the quest is underway.

Said Mountain, “Just imagine the moment, when we find potential signatures of life. Imagine the moment when the world wakes up and the human race realizes that its long loneliness in time and space may be over — the possibility we’re no longer alone in the universe.”

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• 16 October 2023

How would we know whether there is life on Earth? This bold experiment found out

• Alexandra Witze

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Anything down there? Earth as seen by the Galileo probe in 1990. Credit: NASA/JPL

It began the way many discoveries do — a tickling of curiosity in the back of someone’s mind. That someone was astronomer and communicator Carl Sagan. The thing doing the tickling was the trajectory of NASA’s Galileo spacecraft, which had launched in October 1989 and was the first to orbit Jupiter. The result was a paper in Nature 30 years ago this week that changed how scientists thought about looking for life on other planets.

The opportunity stemmed from a tragic mishap. Almost four years before Galileo’s launch, in January 1986, the space shuttle Challenger had exploded shortly after lift-off, taking seven lives with it. NASA cancelled its plans to dispatch Galileo on a speedy path to Jupiter using a liquid-fuelled rocket aboard another space shuttle. Instead, the probe was released more gently from an orbiting shuttle, with mission engineers slingshotting it around Venus and Earth so it could gain the gravitational boosts that would catapult it all the way to Jupiter.

On 8 December 1990, Galileo was due to skim past Earth, just 960 kilometres above the surface. The tickling became an itch that Sagan had to scratch. He talked NASA into pointing the spacecraft’s instruments at our planet. The resulting paper was titled ‘A search for life on Earth from the Galileo spacecraft’ 1 .

The outside view

We are in a unique position of knowing that life exists on Earth. To use our own home to test whether we could discern that remotely was an extraordinary suggestion at the time, when so little was known about the environments in which life might thrive. “It’s almost like a science-fiction story wrapped up in a paper,” says David Grinspoon, senior scientist for astrobiology strategy at NASA’s headquarters in Washington DC. “Let’s imagine that we’re seeing Earth for the first time.”

It came at a time, too, when the search for life elsewhere in the Solar System was at a low ebb. US and Soviet robotic missions in the 1960s and 1970s had revealed that Venus — once thought to be a haven for exotic organisms — was hellishly hot beneath its dense clouds of carbon dioxide. Mars, crisscrossed by the ‘irrigation canals’ of astronomers’ imagination 2 , was a seemingly barren wasteland. In 1990, no one yet knew about the buried oceans that lay on Jupiter’s moon Europa — a discovery that Galileo would go on to make 3 — or on Saturn’s moon Enceladus, both of which are now seen as potential cradles of extraterrestrial life.

Crucially, Sagan and his collaborators took a deliberately agnostic approach to the detection of life, says astrobiologist Lisa Kaltenegger, who heads the Carl Sagan Institute at Cornell University in Ithaca, New York. “Of course he wants to find life, every scientist does,” she says. “But he says, let’s take that wish and be even more cautious — because we want to find it.” The existence of life was to be, in the words of the paper, the “hypothesis of last resort” for explaining what Galileo observed.

But even through this veil of scepticism, the spacecraft delivered. High-resolution images of Australia and Antarctica obtained as Galileo flew overhead did not yield signs of civilization. Still, Galileo measured oxygen and methane in Earth’s atmosphere, the latter in ratios that suggested a disequilibrium brought about by living organisms. It spotted a steep cliff in the infrared spectrum of sunlight reflecting off the planet, a distinctive ‘red edge’ that indicates the presence of vegetation. And it picked up radio transmissions coming from the surface that were moderated as if engineered. “A strong case can be made that the signals are generated by an intelligent form of life on Earth,” Sagan’s team wrote, rather cheekily.

A powerful control

Karl Ziemelis, now chief physical sciences editor at Nature , handled the paper as a rookie editor. He says it remains one of his favourites — and one of the hardest to get in. Editorial approval for the paper was far from unanimous, because it was not obviously describing something new. But, according to Ziemelis, that was mostly beside the point. “It was an incredibly powerful control experiment for something that wasn’t really on many people’s radar at the time,” he says.

“While the answer was known, it profoundly changed our way of thinking about the answer,” says Kaltenegger. Only by stepping back and regarding Earth as a planet like any other — perhaps harbouring life, perhaps not — can researchers begin to get a true perspective on our place in the Universe and the likelihood of life elsewhere, she says.

No sign of civilization in Australia. Credit: NASA/JPL

It takes on a new importance given developments since the Galileo flyby. In 1990, no planets orbiting stars other than the Sun were known. It was another two years before astronomers conclusively reported the first ‘exoplanet’ orbiting a rotating dead star known as a pulsar 4 , and three years more before they found 5 the first around a Sun-like star, 51 Pegasi. Today, scientists know of more than 5,500 exoplanets, few of which look like anything in the Solar System. They range from ‘super-Earths’ with bizarre geologies and ‘mini-Neptunes’ with gassy atmospheres to ‘hot Jupiters’, huge planets whirling close to their blazing stars.

When Sagan and his colleagues pointed Galileo at Earth, they invented a scientific framework for looking for signs of life on these other worlds — one that has permeated every search for such biosignatures since. Kaltenegger still gives Sagan’s paper to her students to show them how it is done. Life is the last, not first, inference to draw when seeing something unusual on another planet, she tells them. Extraordinary claims require extraordinary evidence.

The right mix for life

This lesson could not be more important today, as scientists stand on the verge of potentially revolutionary, and perhaps monumentally confusing, discoveries by the powerful James Webb Space Telescope (JWST). The telescope is just beginning its remote exploration of the atmospheres of dozens of exoplanets, hunting for the same sort of chemical disequilibrium that Galileo spotted in Earth’s atmosphere. It is already turning up early hints of biosignatures that might lead scientists and the public astray.

For instance, JWST has sniffed out methane in the atmosphere of at least one planet. That gas is a powerful signature of life on Earth, but it can also come from volcanoes, no life required. Oxygen captures scientists’ attention because much of it is generated by life on Earth, but it can also be formed by light splitting apart molecules of water or carbon dioxide. Finding the right combination of methane and oxygen could indicate the presence of life on another planet — but that world needs to be located in a temperate zone, not too hot nor too cold. Getting the right mix of life-sustaining ingredients in a life-friendly environment is challenging, Kaltenegger says.

The same is true for other intriguing mixes of atmospheric gases. Just last month, astronomers sifting through JWST data reported finding methane and carbon dioxide in the atmosphere of a large exoplanet called K2-18 b. They suggested that the planet might have water oceans covering its surface, and hinted at tantalizing detections of dimethyl sulfide, a compound that, on Earth, comes from phytoplankton and other living organisms 6 .

Headlines ran wild, with news stories reporting possible signs of life on K2-18 b. Never mind that the presence of dimethyl sulfide was reported with low confidence and needed further validation. Nor that no water had actually been detected on the planet. And, even if water were present, it might be in an ocean so deep as to choke off all geological activity that could maintain a temperate atmosphere.

Building evidence

Challenges such as these led Jim Green, a former chief scientist at NASA, to propose a framework in 2021 for how to report evidence for life beyond Earth 7 . A progressive scale, from one to seven, for example, could help to convey the level of evidence for life in a particular discovery, he argues. Maybe you’ve got a signal that could result from biological activity — that would just be a one on the scale. You’d need to work through many more steps, such as ruling out contamination and acquiring independent evidence of the strength of that signal before you could get to level 7 and demonstrate a true discovery of life beyond Earth.

It could take a long time. A telescope might sniff out an intriguing molecule, and scientists would argue about it. Another telescope might be built to work out the context of the observation. Each brick of evidence must be placed on top of another, each layer of mortar mixed through the arguments, scepticism and agnosticism of many, many scientists. And that’s assuming that life on another world resembles that on Earth — an assumption underlying the conclusions drawn from Galileo’s observations. “The uncertainty may last years or decades,” Grinspoon says. Sagan, who died in 1996, would have loved it.

The same year that Galileo observed Earth, Sagan convinced NASA to point another spacecraft in a direction the agency had not been planning. As Voyager 1 raced past Neptune on its way out of the Solar System, it turned its cameras back towards Earth and photographed a tiny speck, gleaming in a sunbeam. This was the iconic Pale Blue Dot image that inspired Sagan to ruminate in his 1994 book Pale Blue Dot : “That’s here. That’s home. That’s us.”

That fragile gleaming pixel reshaped how humanity visualizes its place in the Cosmos. So, too, did using Galileo to look for life on Earth, says Kaltenegger: “This is how we can use our pale blue dot to provide a template for the search for life on other planets.”

Nature 622 , 451-452 (2023)

doi: https://doi.org/10.1038/d41586-023-03230-z

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Life on Other Planets Essay Example

A major discussion and debate has arisen among scientists and the general public about life on other planets, and whether or not it is possible. While it is possible for there to be life on other planets, a bigger question is brought up: whether or not the other planets can develop and sustain complex life, equivalent to that of Earth. While many do think the universe is too large for there not to be a human race equivalent, it is rebuked by facts and probability about the multitude of conditions needed for comparable advanced life to thrive and even simpler the conditions for the planet itself to be comparable to Earth. An analysis of the facts given in the article, “The Two Billion Earthlike Planets in the Milky Way” by Casey Kazan proves moreover that it is nearly impossible for equivalent life to exist. 

There is the argument made by many that the number of planets in the universe is so great that at least one other planet should be able to sustain life. Even though not found quite yet, there is much speculation around life being found relatively soon on other planets in our solar system. For example, “... life on the microbial level will be discovered sometime in the next twenty years on Mars or on one of Jupiter or Saturn’s moons” (Kazan, 2). Also, there is an attempt to back up this possibility with the fact that these planets have similar components to Earth, such as mass, size, and even the chemical elements that are present; these are all pivotal in establishing an environment crucial to forming and sustaining any form of life. Due to these components, many have come to believe that the possibility of life could be possible and it just has not been discovered yet. 

However, all of these supporting claims can be rebutted by the main fact that to be similar to Earth all of the factors need to align. For example, “Size alone, for example, doesn’t say enough about habitability” (Kazan, 1), this proves that there needs to be a variety, if not all, of the same components to create a similar planet capable of sustaining life as it is known on Earth. All components of the planet must be similar if not the same, as well as aspects such as the stars of this planet, the surrounding planets, and a moon that stabilizes the planet's tilt, to name a few. Lastly, major events that laid the pathway for Earth's evolution need to align such as giant impacts, and even more simply, biological evolution. Additionally, with all of these factors taken into consideration, it was found that “... the zones and regions of the known universe described below are the ones that astrobiologists have concluded have little or zero chance of supporting life as we know it” (Kazan, 2). While the possibility of short-term life on other planets is possible it can not be compared to that of life on Earth and its processes of evolution. After a deep analysis and understanding, it is clearly accepted that the statistics given in the document about the probability of a planet having the same evolutionary processes from the planet itself to the organisms created is nearly impossible.

Overall, the possibility of life existing on other planets similar to Earth is widely debated, but data inevitably the data shows that it is nonviable for this comparable planet to exist. Also, the theory’s behind the possibility of this planet are just abstract possibilities based on just that, possibilities but not factual data. The last thing to think about in this debate is whether or not we humans can aid in the creation and sustainability of potential life on these Earth-like planets in the years to come. Until there is the exploration of this comparable planet found somewhere in the galaxy it is widely accepted that Earth is the only of its kind able to support complex life.

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Life on Other Planets Essay

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Article discussions, works cited.

The article chosen for this part of the assignment is titled “The Extremely Halophilic Microorganisms, a Possible Model for Life on Other Planets,” written by Sergiu Fendrihan, and published in 2017 in Current Trends in Natural Sciences journal. The researchers have analyzed the microscopic life that exists in areas of extreme heat, where water supply exists in the form of salt lakes (Fendrihan 148). Such areas include the Dead Sea, located in the Middle East, as well as various smaller salt lakes found in Africa and Australia.

What these locations have in common is the extremity of conditions in which microorganisms have to exist. According to Fendrihan (148), there is a multitude of halophilic and halotolerant microorganisms inhabiting these areas, up to 159 different subspecies belonging to the Halobacteriaceae family. In addition, these organisms prove to be very resistant to other extremes, such as UV radiation, heat, and lack of nutrients necessary for other bacteria.

Due to the extreme resistance of these bacteria to various hazards, this study provides important data for discovering life on other planets and moons. Mars exhibits signs of water having been present on its surface. In addition, evidence of salty underground oceans has been found on the moons of Saturn and Jupiter (Enceladus and Europa).

Thus, studying halophilic microorganisms supports the possibility of the existence of life on planets previously deemed uninhabitable. Low requirements for water and nutrients as well as high resistance to the elements increases their chances of survival. Investigating these planets would enrich the existing knowledge of space and biology.

The article titled “Life on Mars: Exploration and Evidence” by Nola Taylor Redd provides cursory information about the state of research regarding life on Mars. The planet used to have large water deposits that were lost due to irradiation and exposure to harsh temperatures. The article suggests that life on Mars may still exist underneath the surface of the planet (Redd). Question: What exactly happened that altered Mars’s climate and caused it to lose so much of its water?

The second article titled “Aliens May Well Exist in a Parallel Universe, New Studies Find” by Brandon Specktor speculates about the existence of life in other dimensions. This article seems more like speculation rather than a contribution to the scientific community, as evidence of the existence of other dimensions is purely theoretical (Specktor). Question: If parallel universes exist, can they influence the events in our universe?

The third article titled “The Four Best Places for Life in Our Solar System” by Nicole Mortillaro provides a summary of four potential places for finding life. These planets and moons include Mars, Europa, Enceladus, and Titan (Mortillaro). This article outlines the requirements currently used to determine the feasibility of life on other planets. Question: Why did NASA restrict itself to studying Mars instead of sending a drone on one of the moons?

The fourth article written by Mike Wall speaks of the protective gravitational barrier of our solar system, which filters out charged particles coming from outside of the solar system. The existence of this protective field makes life on Earth possible (Wall). Studying it would help determine which systems can potentially harbor life and which could not. Question: Is the gravitational barrier unique to the Solar system alone?

The fifth article written by Lisa Kaspin-Powell explores the potential of non-H2O-based lifeforms existing on Titan. The article informs the readers that the elements found in Titan’s atmosphere can form cellular membranes similar to phospholipid molecular chains (Kaspin-Powell). Question: What other elements could potentially form cellular membranes?

The last article written by Seth Shostack provides a list of eight planets within the scope of our solar system that has the potential of harboring life. Aside from the 4 candidates mentioned in the article by Mortillaro, the article adds Earth, Venus, Ganymede, and Callisto, which show gravitational signs of possessing underground water (Shostak). Question: How is gravity related to the presence or absence of water?

Fendrihan, Sergiu. “The Extremely Halophilic Microorganisms, A Possible Model for Life on Other Planets.” Current Trends in Natural Sciences, vol. 6, no. 12, 2017, pp. 147-151.

Kaspin-Powell, Lisa. “Does Titan’s Hydrocarbon Soup Hold a Recipe for Life?” Astrobiology Magazine . 2018. Web.

Mortillaro, Nicole. “ The Four Best Places for Life in Our Solar System .” Global News . 2014. Web.

Redd, Nola Taylor. “ Life on Mars: Exploration and Evidence. ” Space. 2017. Web.

Shostak, Seth. “ 8 Worlds Where Life Might Exist. ” Space. 2006. Web.

Specktor, Brandon. “ Aliens May Well Exist in a Parallel Universe, New Studies Find. ” Space. 2018. Web.

Wall, Mike. “ NASA Will Launch a Probe to Study the Solar System’s Protective Bubble in 2024. ” Space. 2018. Web.

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The Great Galaxy M–31 in the constellation Andromeda. This is the nearest galaxy to our own, and resembles it in many ways. The dark rifts are enormous cosmic dust clouds from which stars are thought to form. In each galaxy there may be 100 million planets on which life exists. (University of Chicago Photographic Archive, apf6-02681 , Special Collections Research Center, University of Chicago Library)

From our print archive: In spite of the hours clocked at super-spyglasses, astronomers have yet to spot any little green men on Mars or any other planet. But they have made some pretty convincing observations that life does exist on other planets.

Is there life on other worlds? If other planets can support life chemically as we know it here on earth, how does this relate to the origin of life itself?

Scientists have long speculated on the theory that life in its most primitive form may be the next step in cosmic evolution after the formation of planets. While this is still only a theory, new ideas on planetary origin and recent discoveries in chemistry have given it support.

For example, forty million miles from Earth, at this writing, is Mars, a planet colder than the earth, with no oxygen in its atmosphere, and little water on its surface. A man transported to Mars would gasp and die—and most other familiar organisms would also perish.

Yet, for over half a century astronomers have observed slight seasonal color variations on the planet; variations apparently coinciding with the availability of water. These have been interpreted as evidence for plant life on Mars, life specifically adapted to the rigors of the Martian environment. If the reported color changes are real, there seems to be no other reasonable interpretation.

Further, marginal spectroscopic observations by W. M. Sinton suggest that there may be molecules with C-H bonds on the surface of Mars. Carbon and hydrogen are fundamental elements for all terrestrial organisms, and the chemical bond combining them is essential for the structure of proteins, nucleic acids, and other biological building blocks. Is it possible, then, that the same sort of life, similar in its basic chemical makeup, has originated twice in the same solar system? While speculative in some of its details, the general pattern of cosmic evolution is fairly well established.

Cosmic evolution begins with an enormous cosmic dust cloud, such as exists today between the stars. Such a cloud has a “cosmic” abundance of the elements, being composed primarily of hydrogen and helium, with only a small admixture of heavier elements. Here and there matter will be somewhat more dense than in nearby regions. The more diffuse regions will be gravitationally attracted to the denser region, which, in consequence, will grow in size and mass. As matter streams in towards the condensing central nucleus, conservation of angular momentum will cause the whole region, nucleus and streaming matter, to rotate faster and faster.

In addition, as large amounts of matter continue to collide with the nucleus, its temperature will steadily rise. After perhaps a hundred million years, the temperature at the center of the cloud will have risen to about fifteen million degrees. This is the ignition temperature for thermonuclear reactions, (such as the conversion of hydrogen to helium in the hydrogen bomb). At this time the nucleus of the cloud will become a star, “turning on” and radiating light and heat into nearby space. If the rotation is sufficiently fast, the forming star will separate under certain conditions into smaller parts, producing a double or multiple star system.

Now as the star forms, there still is a large dust cloud surrounding the star and rotating with it. In this cloud, the solar nebula, small, denser regions begin attracting nearby matter, as in star formation. However, the protoplanets that grow from these regions, (in the gravitational field of the nearby star), never rise by collisional heating to the thermonuclear ignition temperature, and so become planets and not stars.

Gerard P. Kuiper, professor of astronomy at Yerkes Observatory, has described how planets are formed in this manner in recent years. In the forming protoplanets, there would be a tendency for the heavier elements to sink to the center, leaving the much more abundant hydrogen and helium as the principal constituents of the atmosphere surrounding the new planets. When the newly formed star “turns on,” radiation pressure will tend to blow away this atmosphere.

However, if the protoplanet is very massive, or very far from the sun, the gravitational attraction of the protoplanet for a gas molecule may be greater than the force of radiation trying to blow it away, and the protoplanet may retain an atmosphere. This atmosphere can be residual from the proto-atmosphere, or may be due to gaseous exhalations from the planetary interior. For example, the earth’s present atmosphere is due to exhalations; Jupiter’s present atmosphere is residual.

In such a way, one can understand, generally, the atmospheres of the planets in this solar system:

• Mercury : Not massive, close to the sun, retains negligible atmosphere.
• Venus : More massive than Mercury, further from the sun, retains only the heavy gas, carbon dioxide.
• Earth : Retain s the lighter gases, nitrogen, oxygen, and water vapor, but has lost almost all hydrogen and helium.
• Mars : Although further from the sun, is less massive than Earth or Venus, and so retains principally only the heavy gas, carbon dioxide.
• Jupiter, Saturn, Uranus, Neptune : Much further from the sun and very massive, they retain much hydrogen and helium, while the other planets have lost theirs.

One fact about our solar system that has rung the death knell of many cosmogonies is the fact that although over 99 per cent of the mass of the solar system is in the sun, over 98 per cent of the angular momentum of the system is in the planets. It is as if the rotational inertia has been transferred from the sun to the planets. H. Alfven has explained this as a magnetic braking of the sun’s rotation, due to the interaction of “its magnetic field with the ionized solar nebula. On this basis, the existence of a solar nebula from which planetary systems form will cause the central star to rotate more and more slowly.

Now the origin of planets must be dependent on the temperature of the central star. If it is too cold, the atmosphere of the protoplanets will not be blown away, resulting perhaps in the formation of a system of planets similar to Jupiter, but even larger and more massive. On the other hand, if the star is too hot, radiation pressure will disperse the solar nebula rapidly, leaving, if anything, small atmosphereless planets, or a system of millions of tiny asteroids. For planets to be formed, the temperature of the star must be between these extremes.

There is another reason to believe that hot stars do not have planets. If the formation of planetary systems and the slowing down of stellar rotation both arise from the existence of solar nebulae, then we should expect the hot stars which dissipate their solar nebulae and do not form planets to rotate faster. This is exactly what is observed! The hotter the star, the faster the rotation. Cooler stars rotate more slowly than would otherwise be expected.

At a temperature of about 7,000 degrees, characteristic of what are called F stars, there is a sudden large decrease in average rotational velocities, and it is possible, perhaps, that below this temperature all stars retain enough of their solar nebulae to form planets, (provided they have not used up their solar nebulae in forming double or multiple sun systems).

The number of such stars is between one and ten per cent of the total number of stars, suggesting that there are as many as ten billion solar systems in our galaxy alone. Of these, perhaps one per cent, or 100 million have planets like the earth. What is the probability of life on these worlds?

Since the most abundant element, cosmically, is hydrogen, the atmosphere of the early protoplanets of any system must contain much hydrogen and hydrogen compounds. The hydrogen compounds of carbon, nitrogen, and oxygen are probably the most abundant hydrogen compounds in the proto-atmosphere. They are, respectively, methane, CH4, ammonia, NH3, and water vapor, H20.

In 1953, Stanley Miller, PhD’54, then a graduate student working under professor Harold C. Urey showed that when hydrogen, methane, ammonia, and water vapor are mixed together, and supplied with energy, some fundamental organic compounds are produced. (The energy source in protoatmospheres is probably ultraviolet light from the sun about which the protoplanet revolves.)

These compounds are almost all amino acids, the biochemical building blocks from which protein is constructed. There is also some reason to believe that amino acids lead to the formation of purines and pyrimidines, which are in turn building blocks for nucleic acids. Proteins and nucleic acids are the two fundamental constituents of life as we know it on earth; hereditary materials such as genes and chromosomes are composed perhaps exclusively of nucleic acids and proteins. In addition, enzymes, which catalyze slow chemical reactions and thereby make complex life forms possible, are always proteins.

Experiments of comparable importance to those of Miller have been performed by S. W. Fox. Fox applied heat, in the range between 100 and 200 degrees Centigrade, to simple molecules, such as those synthesized by Miller. This simple procedure produced small amounts of complex organic molecules that happen to be widely distributed in all terrestrial organisms. In particular, Fox has produced ureidosuccinic acid, a key intermediary in the synthesis of nucleic acids. The temperatures required by Fox can easily be supplied by radioactive heating of the crust of the planet. There is evidence that such radioactive heating is a normal part of the early evolution of all planets.

Now it is really striking that the molecules produced by Miller and Fox are precisely the molecules necessary to form life as we know it. Almost no molecules were produced which are not fundamentally involved in modern terrestrial organisms.

The processes described by Miller and Fox would probably occur on at least one planet of each star of moderate temperature. All that is required is a way of collecting the molecules produced by these processes into one place where they can interact. A liquid medium on the surface of the planet serves this purpose admirably. Molecules produced in the atmosphere would fall into these bodies of liquid, and molecules produced on land by the application of heat would also be washed into them. Although seas of liquid ammonia or hydrofluoric acid would serve, it can be shown that seas of water would be most efficient in collecting and preserving the bio-molecules.

The one planet in each system that we are considering probably possessed liquid water seas early in its history, and therefore on such planets the production of proteins and nucleic acids may be expected.

Now proteins and nucleic acids have some unusual properties; so far as we know, ones not found in any other molecules. They can form a new molecule which not only can construct other identical molecules from the matter floating in the sea around it, but which if changed in some way can also construct copies of its changed structure. Such a mutating, self-reproducing molecule or collection of molecules must undergo natural selection. For these reasons, it must be identified as the first living being on the planet in question.

Thus, there may be 100 million planets in this galaxy alone on which flourish organisms at least biochemically akin to ourselves. On the other hand, due to natural selection, these organisms must be well adapted, each to its own environment. Since even slight differences in the environment eventually cause extreme differences in the structure of organisms, we should not accept extraterrestrial lifeforms to resemble anything familiar. But there is reason to believe they are out there.

Living on Other Planets: What Would It Be Like?

Have you ever wondered what it would be like to live on the moon? What about Mars, or Venus or Mercury? We sure have and that's why we decided to find out what it might be like to live on other worlds in our solar system, from Mercury to Pluto and beyond in a new, weekly 12-part series.

For this series, written by Space.com contributor Joseph Castro, we wanted to know what the physical sensation of living on other worlds would be like: What would the gravity be like on Mercury; How long would your day be on Venus? What's the weather on Titan ?

For the sake of our solar system tour, let's take it as a given that humanity has the futuristic tech needed to set up a base on the planets. So join Space.com each week as we skip across the solar system and see what it would feel like to live beyond Earth. Check out our schedule for the tour through the solar system and beyond below:

Wednesday, Jan. 28 – Mercury

What Would It Be Like to Live on Mercury? The closest planet to the sun is an inhospitable place, and probably not the first choice for human colonization. But if somehow we had the technology, what would it be like for people to live on Mercury?

10 Strange Facts About Mercury (A Photo Tour)   Mercury is a weird place. See just how weird the closest planet to the sun is in our photo tour. 

Living on Mercury Would be Hard (Infogaphic) So you've read what it might be like to be a colonist on Mercury. Now see the details in visual form. Space.com's Karl Tate lays out what livingon Mercury might be like for an astronaut.

More about Mercury:

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Breaking space news, the latest updates on rocket launches, skywatching events and more!

• Planet Mercury: Facts About the Planet Closest to the Sun
• How Was Mercury Formed?
• What is Mercury Made Of?
• Mercury's Atmosphere
• How Hot is Mercury?
• How Far is Mercury From the Sun?
• How Big is Mercury?

Tuesday, Feb. 3 – Venus

What Would It Be Like to Live on Venus? From its hellish temperatures to crushing pressures and volcanoes, the planet Venus might be a hard place for an astronaut to set up camp. Here's what it might be like for an astronaut to live on the second planet from the sun. 

Living on Planet Venus: Why It Would Be Hard (Infographic) If you thought Venus was the perfect vacation spot, better think again. See how some if its most hellish aspects would challenge astronauts in this infographic by Space.com's Karl Tate.

The 10 Weirdest Facts About Venus Venus is the brightest planet in our night sky, and one of the strangest. Take a look at some of the oddest facts about this weird world.

More About Venus: 

• Planet Venus Facts: A Hot, Hellish & Volcanic Planet
• How Was Venus Formed?
• What is Venus Made Of?
• How Hot is Venus?
• Venus' Atmosphere: Composition, Climate and Weather
• How Far Away is Venus?
• How Big is Venus?

Tuesday, Feb. 10 – Earth's Moon

What Would It Be Like to Live on the Moon? From its lack of an atmosphere to dusty surface, the moon wouldn't be the most hospitable place for lunar colonizers to find themselves. Find out how they might be able to make the lunar surface a more cozy place to put down roots.

Living on the Moon: What It Would Be Like: Infographic How could you live on the moon? Space.com's Karl Tate explains some of the odds lunar explorers are up against in this infographic.

The Moon: 10 Surprising Lunar Facts Here are 10 amazing and surprising facts about the moon.

More about the moon : 

• Moon Master: An Easy Quiz for Lunatics
• The Apollo Moon Landings: How They Worked (Infographic )
• How the Moon Evolved: A Photo Timeline
• Apollo Quiz: Test Your Moon Landing Memory
• What is the Moon Made Of?
• How Far is the Moon?
• What is the Temperature on the Moon?

Tuesday, Feb. 17 – Mars

What Would It Be Like to Live on Mars? Humans have long-dreamed about potentially colonizing the Red Planet, but what would it really take for humans to comfortably live on Mars?

How Living on Mars Could Challenge Colonists (Infographic ) What kind of challenges would humans face when trying to set up shop on Mars? The thin Martian atmosphere, harsh climate and other factors would make the Red Planet is a tough place for Martian explorers to live, but it could be possible.

More about Mars :

• Moons of Mars: Amazing Photos of Phobos and Deimos
• 10 Years on Mars: Smithsonian Celebrates Spirit, Opportunity Rovers (Photos
• Photos: Ancient Mars Lake Could Have Supported Life
• Mars Myths & Misconceptions: Quiz
• A 'Curiosity' Quiz: How Well Do You Know NASA's Newest Mars Rover?
• How Long Does It Take to Get to Mars?

Tuesday, Feb. 24 – Asteroid Belt

What Would It Be Like to Live On Dwarf Planet Ceres in the Asteroid Belt?   The dwarf Planet Ceres may be round, but it doesn't have much of an atmosphere to speak of. What would it be like for human explorers if they visited this object in the asteroid belt between Mars and Jupiter?

Living On Dwarf Planet Ceres in the Asteroid Belt (Infographic )  Learn more about what it might be like for human beings to live on the dwarf planet Ceres in the asteroid belt. 

More about Ceres and the asteroid belt :

• Mysterious Bright Spots Shine on Dwarf Planet Ceres (Photos )
• Dwarf Planet Ceres Coming Into NASA Probe’s View
• NASA Finds Mysterious Bright Spot on Dwarf Planet Ceres: What Is It?
• The Asteroid Belt Explained: Space Rocks by the Millions (Infographic ) 
• The Greatest Mysteries of the Asteroid Belt
• Asteroid Basics: A Space Rock Quiz  

Tuesday, March 3 – At Jupiter

What Would It Be Like to Live on Jupiter's Moon Europa?   What would human explorers visiting Jupiter's icy moon Europa find when they get there? It's possible some form of life might already be there waiting for them.

Living On Europa Explained: Humans Might Not Be First: Infographic Europa is one of the most viable places in the solar system to hunt for life as we know it, but could humans find a way to settle it?

More about Jupiter and its moons :

• Planet Jupiter: Facts About Its Size, Moons and Red Spot
• Jupiter's Moons: Facts About the Largest Jovian Moons
• Europa: Facts About Jupiter's Icy Moon and Its Ocean
• Jupiter Quiz: Test Your Jovian Smarts
• How Far Away is Jupiter?
• Jupiter's Atmosphere & the Great Red Spot
• What is Jupiter Made Of?
• How Was Jupiter Formed?
• What is the Temperature of Jupiter?
• How Big is Jupiter?
• Photos: Europa, Mysterious Icy Moon of Jupiter
• Photos: The Galilean Moons of Jupiter
• Target: Jupiter — 9 Missions to the Solar System's Largest Planet

Tuesday, March 10 – At Saturn, the Ringed Planet

What Would It Be Like to Live on Saturn's Moons Enceladus and Titan? Saturn might not be a place where huamns could live, but its moons Titan and Enceladus might hold more hope for human colonists.

How Humans Could Live on Saturn's Moon Titan (Infographic) Saturn's moon Titan might be the most hospitable place in the solar system for humans to set up shop. What would it be like for a human explorer to hang out on Titan?

More about Saturn and its moons:

• Submarine Explores Saturn's Moon Titan In NASA Animation
• Planet Saturn: Facts About Saturn’s Rings, Moons & Size
• Saturn's Rings: Composition, Characteristics & Creation
• Saturn's Moons: Facts About the Ringed Planet's Satellites
• Enceladus: Saturn's Tiny, Shiny Moon
• How Big is Saturn?
• How Far Away is Saturn?
• Saturn's Atmosphere: All the Way Down
• What is Saturn Made Of?
• How Was Saturn Formed?
• Cassini-Huygens: Exploring Saturn's System
• Titan: Facts About Saturn's Largest Moon

Tuesday, March 17 – At Uranus

What Would It Be Like to Live on a Moon of Uranus? How would it feel to bounce around in the low gravity of Titania or Miranda? Find out what it might be like to colonize the moons of Uranus.

Living on Titania: Uranus' Moon Explained (Infographic ) Get a close-up look at what it could be like to live on Titania, Uranus' largest moon.

More about Uranus and its moons :

• Moons of Uranus: Facts About the Tilted Planet's Satellites
• How Big is Uranus?
• How Far is Uranus?
• Uranus' Atmosphere: Layers of Icy Clouds
• What is the Temperature of Uranus?
• What is Uranus Made Of?
• How Was Uranus Formed?
• Who Discovered Uranus (and How Do You Pronounce It)?
• Planet Uranus: Facts About Its Name, Moons and Orbit
• Inside Gas Giant Uranus (Infographic )
• Photos of Uranus, the Tilted Giant Planet

Tuesday, March 24 – At Neptune

What Would It Be Like to Live on Neptune's Moon Triton? While Neptune doesn't have much of a solid surface under its layers and layers of gas, its huge moon Triton might be a fun (and maybe difficult) place for humans to settle in the solar system.

Living on Triton: Neptune's Moon Explained (Infographic ) Triton could be an interesting place to live in the solar sytem. Learn more about what the first human settlers of the world could possibly find.

More about Neptune and its moons :

• Triton: Neptune's Odd Moon
• Neptune's Moons: 14 Discovered So Far
• How Big is Neptune?
• How Far Away is Neptune?
• Neptune's Atmosphere: Composition, Climate & Weather
• What is Neptune's Temperature?
• What is Neptune Made Of?
• How Was Neptune Formed?
• Planet Neptune: Facts About Its Orbit, Moons & Rings
• Photos of Neptune, The Mysterious Blue Planet
• Moons of Neptune: Giant Blue Planet's 14 Satellites Unmasked (Infographic )
• Inside Gas Giant Neptune
• Neptune Quiz: How Well Do You Know the Other Blue Planet? 

Tuesday, March 31 – At  Pluto

What Would It Be Like to Live on Pluto? How cold would human settlers on Pluto really be? The mysterious dwarf planet will be explored in closer detail when NASA's New Horizons probe flys by the icy body in July.

Living on Pluto: Dwarf Planet Facts Explained (Infographic)   Learn more about what it might be like to live on Pluto, if humans ever make it that far into the solar system.

More about Pluto and its moons : 

• How NASA's New Horizons Mission to Pluto Works Infographic
• Pluto's 5 Moons Explained: How They Measure Up: Infographic
• Pluto: A Dwarf Planet Oddity: Infographic
• Inside Dwarf Planet Pluto
• Destination Pluto: NASA's New Horizons Mission in Pictures
• Photos of Pluto and Its Moons
• Lowell Observatory: Where Pluto Was Discovered
• Clyde Tombaugh: Astronomer Who Discovered Pluto How Big is Pluto?
• How Far Away is Pluto?
• Does Pluto Have an Atmosphere?
• How Cold is Pluto?
• What is Pluto Made Of?
• How Was Pluto Formed?

Tuesday, April 7 – Following a Comet

What It Would Be Like to Live On a Comet Living on comets requires great care — the gravity is so weak that you could easily jump off the frozen bodies and into space. 

Living on a Comet: 'Dirty Snowball' Facts Explained: Infographic Halley's Comet, a dusty ball of ice and frozen gases, spends most of its time in the chilly outland of the solar system. See what it would be like to live on a comet in this infographic.

More about comets:

• Comets: Facts About The ‘Dirty Snowballs’ of Space
• Comet Quiz: Test Your Cosmic Knowledge
• Halley's Comet: Facts About the Most Famous Comet
• Comet 67P: Target of Rosetta Mission
• Best Close Encounters of the Comet Kind
• Photos: Spectacular Comet Views from Earth and Space

Saturday, May 9 – On a Strange New World 

What Would It Be Like to Live on Alien Planet Kepler-186f? There are many unknowns regarding the potentially habitable exoplanet Kepler-186f, but it may have similar light (from its star) and gravity as Earth. 

Living on an Alien Planet: Exoplanet Kepler-186f: Infographic At last humans are able to make educated guesses about what living on alien worlds might be like. Here's what we know about the alien planet Kepler-186f.

Earth-Size Planet Kepler-186f, a Possibly Habitable Alien World: Gallery The alien planet Kepler-186f is a planet only slightly larger than Earth orbiting inside the habitable zone of its red dwarf star. See images and photos of the Kepler-186f planet discovery in this Space.com gallery.

Exoplanet Kepler-186f: Earth-Size World Could Support Oceans and Life: Infographic A rocky planet that could have liquid water at its surface orbits a star 490 light-years away.

More resources on exoplanets:

• Exoplanets: Worlds Beyond Our Solar System
• Alien Planet Quiz: Are You an Exoplanet Expert?
• How Habitable Zones for Alien Planets and Stars Work: Infographic
• 10 Exoplanets That Could Host Alien Life
• 6 Most Likely Places for Alien Life in the Solar System

Follow us @Spacedotcom , Facebook and   Google+ . 

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected].

Tariq is the Editor-in-Chief of Space.com and joined the team in 2001, first as an intern and staff writer, and later as an editor. He covers human spaceflight, exploration and space science, as well as skywatching and entertainment. He became Space.com's Managing Editor in 2009 and Editor-in-Chief in 2019. Before joining Space.com, Tariq was a staff reporter for The Los Angeles Times covering education and city beats in La Habra, Fullerton and Huntington Beach. In October 2022, Tariq received the Harry Kolcum Award for excellence in space reporting from the National Space Club Florida Committee. He is also an Eagle Scout (yes, he has the Space Exploration merit badge) and went to Space Camp four times as a kid and a fifth time as an adult. He has journalism degrees from the University of Southern California and New York University. You can find Tariq at Space.com and as the co-host to the This Week In Space podcast with space historian Rod Pyle on the TWiT network . To see his latest project, you can follow Tariq on Twitter @tariqjmalik .

Science and music festival Starmus VII is about to rock Bratislava with a stellar lineup

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Powerful new NOAA weather satellite set for June launch atop SpaceX Falcon Heavy

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Life on Other Planets: Finding My Place in the Universe

The William T. Golden Center for Science and Engineering | AAAS Headquarters Building 1200 New York Avenue NW. Washington , DC 20005 United States

With nearly 6,000 planets discovered beyond the Solar System, humankind is closer than it has ever been to answering the question: “Are we alone in the universe?” And yet, much remains to be done. Many factors and processes can affect planetary climate and habitability, and their effects must be understood to accurately determine a planet's potential for hosting life. Professor Shields will describe the methods her research group uses to quantify the effects on planetary climate of a range of factors that are currently unconstrained by observations. She will share recent results from this work using a hierarchy of computer models, and discuss the implications of these results for planetary habitability and the identification of those planets most capable of supporting life. Sharing excerpts from her new memoir, Life on Other Planets , Shields will also speak about her struggle to fit in as a Black woman in astronomy, her nontraditional career path, and the holistic ways of working soft and resting more that were instrumental to finding her place in the universe, and thriving both personally and professionally.

Dr. Aomawa Shields is an astronomer, astrobiologist, classically trained actor, and writer. She is the Clare Boothe Luce Associate Professor in the Department of Physics and Astronomy at the University of California, Irvine (UCI). She was named a 2015 TED Fellow and is the recipient of the National Science Foundation’s CAREER award and NASA Habitable Worlds and Exoplanets Research Program grants, among others. She is the founder and director of Rising Stargirls, a program dedicated to encouraging girls of all colors and backgrounds to learn about, explore, and discover the universe using theater, writing, and visual art. Her new memoir, Life on Other Planets: A Memoir of Finding My Place in the Universe , was published by Viking in July 2023. Shields has presented her book in various events and has been showcased on Good Morning America, MSNBC, Talks at Google and many more. She is the proud mother of 6-year-old rising stargirl Garland-Rose, who she and husband Steven have deemed the most extraordinary lifeform in their universe.

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Extraterrestrial Life Essay

This extraterrestrial life essay is about the search for other life forms on other planets, and whether you think the money spent on this is better spent elsewhere. 

Take a look at the essay question.

Some people believe that using taxpayer funds to look for life on other planets is important. Others, however, think that it is a waste of public money because there are much more important issues requiring funding on our own planet.

Discuss both views and give your opinion.

Understanding the question & brainstorming

The question for this extraterrestrial life essay is fairly straightforward to understand. You need to discuss:

• The pros of looking for life on other planets
• The cons of this (in terms of neglecting important issues on earth)
• Your opinion

It's a bit more of a tricky question though in that you need to come up with some ideas of why it is beneficial to find alternative life. This could involve using some complex language, so you need to be careful with your response.

Dealing with 'Your Opinion'

Remember that you don't have to have a separate body paragraph on ' Your Opinion '. 

A problem that can arise when candidates do this is that they end up with quite short and weak body paragraphs overall as it's difficult to have time to fully explain everything in 40 minutes in three strong body paragraphs.

It can also lead to repetition. Candidates often end up repeating in their opinion paragraph what they have already said in a previous paragraph. 

A solution is to make the second body paragraph your opinion instead, then reiterate this in the conclusion.

Now take a look at the extraterrestrial life essay model answer.

Extraterrestrial Life Essay Sample

You should spend about 40 minutes on this task.

Write about the following topic:

Give reasons for your answer and include any relevant examples from your own experience or knowledge.

Write at least 250 words.

Model Answer

The search for extraterrestrial life has been a topic of discussion and debate for many years. While some people believe that using taxpayer funds to find life on other planets is essential, others see it as a poor use of public money.

Those who believe in the importance of searching for extraterrestrial life argue that this is an opportunity to answer one of the biggest questions in science and human history: are we alone in the universe? They also believe that such a search will have tremendous scientific and technological benefits, including the development of new instruments, techniques, and methods of exploration that can be used for other purposes. Moreover, the discovery of extraterrestrial life, even if only in the form of microbial organisms, would have a profound impact on our understanding of the universe and the origin of life itself.

That said, I personally hold the view that though such research is important, the money spent on this should be balanced against other important needs and should not come at the expense of other critical programs. There are many pressing issues on our own planet that require funding, such as the major problems of poverty, hunger, disease, and environmental degradation. These are all urgent issues that affect millions of people around the world. We need to be mindful of the limited resources available to us and make sure that they are used in a responsible and effective manner.

In conclusion, the search for extraterrestrial life is an important and fascinating endeavour, but it must be balanced against other critical needs. The investment in this area should be used wisely and effectively, taking into account the benefits and limitations of the research, and should not be to the detriment of other important programs.

This extraterrestrial life essay would score highly for IELTS as it clearly answers the question, discussing both sides of the issues and providing the writers opinion. Ideas have supporting evidence and examples. 

It has good coherence and cohesion as it's well-organised into paragraphs and makes use of discourse markers and linking words well.

There are good examples of lexis and collocations, many of which are topic-related. For example:

• tremendous scientific and technological benefits
• development of new instruments, techniques, and methods of exploration
• the form of microbial organisms
• have a profound impact
• origin of life itself

There are also good examples of accurate and effective grammatical forms and sentences. For instance:

• Those who believe in the importance of searching for extraterrestrial life argue that this is an opportunity to answer one of the biggest questions in science and human history.
• ...will have tremendous scientific and technological benefits, including the development of new instruments, techniques, and methods of exploration that can be used for other purposes
• ...the discovery of extraterrestrial life, even if only in the form of microbial organisms, would have ...

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Are We Alone?

The search for life beyond Earth is really just getting started, but science has an encouraging early answer: there are plenty of planets in the galaxy, many with similarities to our own. But what we don’t know fills volumes.

Observations from the ground and from space have confirmed thousands of planets beyond our solar system . Our galaxy likely holds trillions. But so far, we have no evidence of life beyond Earth. Is life in the cosmos easily begun, and commonplace? Or is it incredibly rare?

More questions than answers

In the thousands of years humanity has been contemplating the cosmos, we are the first people to know one thing for sure: The stars beyond our Sun are teeming with planets . They come in many varieties, and a good chunk of them are around the size of Earth . Like most scientific questions, though, getting an answer to this one just breeds more questions: Which, if any, of these exoplanets harbors some form of life? How quickly does life get its start? And how long does it last?

Where is everybody?

The universe's eerie silence has its own name – the "Fermi paradox." Physicist Enrico Fermi famously posed the question: "Where is everybody?" Even at slow travel speeds, the universe's billions of years of existence allow plenty of time for intelligent, technological lifeforms to traverse the galaxy. Why, then, is the cosmos so quiet?

Meanwhile, exoplanet discoveries over the past two decades have filled in a few of the terms in the much-debated Drake Equation – a chain of numbers that might one day tell us how many intelligent civilizations we can expect to find. Most of its terms remain blank – the fraction of planets with life, with intelligent life, with detectable technology – but the equation itself suggests we might one day arrive at an answer. It feels at least a little more hopeful than Fermi's silence.

We stand at a crossroads in the search for life. We've found thousands of planets in our Milky Way galaxy, a large fraction of them in Earth's size range and orbiting in their stars' "habitable zones" – the distance from the star at which liquid water could exist on the surface. We know the galaxy likely holds trillions of planets. Our telescopes in space and on the ground, and our remote-sensing technology, grow ever more powerful. Yet so far, the only life we know of is right here at home. For the moment, we're staring into the void, hoping someone is staring back.

Next: We don't have a universally accepted definition of life itself, so can we find life?

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Essay on Possibility Of Life On Other Planets

Students are often asked to write an essay on Possibility Of Life On Other Planets in their schools and colleges. And if you’re also looking for the same, we have created 100-word, 250-word, and 500-word essays on the topic.

Let’s take a look…

100 Words Essay on Possibility Of Life On Other Planets

Is there life beyond earth.

Our universe is vast, filled with stars and planets. Scientists believe there might be life on other planets besides Earth. They study space, looking for places that have water and the right temperatures for life.

Searching the Skies

Telescopes help scientists find planets in far-away solar systems. They look for signs that these planets could support life, like having an atmosphere and being not too hot or cold.

Missions to Mars

Mars is our neighbor and has been explored by robots. These robots send back pictures and check if there’s water or signs of past life.

Moons and Beyond

Some moons around other planets might have oceans under their icy surfaces. These hidden seas could be homes for alien creatures.

Life’s Ingredients

Life needs more than water. It needs the right chemicals and energy sources. Scientists are trying to understand what mix might mean life exists somewhere else.

250 Words Essay on Possibility Of Life On Other Planets

Many people wonder if we are alone in the universe or if other planets have living things like us. Scientists are working hard to find the answer. They look at planets and moons to see if they have what life needs to survive.

What Life Needs

All living things on Earth need water, food, and the right temperature to live. So, scientists search for places with water because it’s very important for life. They also look for air that living things can breathe and not too hot or too cold temperatures.

Planets Like Earth

Our Earth is just right for life because it’s not too close or too far from the Sun. This makes the temperature good for water to stay liquid. Scientists have found other planets that are a bit like Earth, in what they call the “Goldilocks Zone.” These planets might have the right conditions for life.

Moons and Microbes

It’s not just planets that could have life. Some moons around other planets have oceans under their icy surfaces. Tiny life forms called microbes might live there. These microbes don’t need sunlight; they can live off chemicals in the water.

Looking for Signs

Spacecraft and telescopes help scientists look for signs of life far away. They can find out what’s in the air of other planets and see if it’s like Earth’s air. They also look for signs of water and chemicals that living things make.

In summary, the possibility of life on other planets is a big question that excites many. With space exploration, we keep searching for answers, hoping to find out if we have neighbors in the vast universe.

500 Words Essay on Possibility Of Life On Other Planets

The universe is huge, with countless stars and planets. For a long time, people have wondered if there are other living things somewhere out there. With new tools and technology, scientists are getting closer to finding an answer.

What Makes a Planet Livable?

To support life as we know it, a planet needs certain things. Water is very important because all living things on Earth need it. The planet should not be too hot or too cold, which means it has to be at just the right distance from its star. This area is called the “Goldilocks Zone.” Also, the air should have gases that living things can breathe.

Scientists use powerful telescopes to look at faraway planets. They are finding many that might have the right conditions for life. These planets are called “exoplanets.” Some of them have signs of water and the right temperature range. This makes them interesting places to look for life.

Robots and Space Probes

Robots and space probes are sent to other planets and moons in our solar system. They take pictures, collect samples, and send back information. Mars, for example, has robots on it right now. These robots are checking if there was ever life there. They look for water, chemicals, and other signs that could mean Mars once had living things.

What Could Alien Life Look Like?

If there is life on other planets, it might be very different from what we see on Earth. It could be tiny bacteria or something we can’t even imagine. The conditions on other planets are not the same as Earth, so life there might have adapted in strange ways.

Challenges in Finding Life

Finding life on other planets is not easy. Space is so big that it takes a long time to get information. Sometimes, the signs of life are hard to spot or could be caused by something else. Scientists have to be very careful and check everything many times.

What Does This Mean for Us?

Thinking about life on other planets is exciting. It can teach us more about our own planet and how life started here. It also makes us think about our place in the universe. Are we alone, or is there a big family of living things out there?

In conclusion, the possibility of life on other planets is a question that makes us curious. With new discoveries and technology, we might find answers someday. Until then, we keep looking up at the stars and wondering.

That’s it! I hope the essay helped you.

If you’re looking for more, here are essays on other interesting topics:

• Essay on My Social Upbringing
• Essay on My Swimming Experience
• Essay on My Talent Is Drawing

Apart from these, you can look at all the essays by clicking here .

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Why do astronomers look for life on other planets based on what life is like on Earth

The Conversation

Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to [email protected] .

Why do astronomers look for signs of life on other planets based on how life is on Earth? Couldn’t there be totally different kinds of life on other planets? – Henry, age 13, Somerville, Massachusetts

Have you ever played hide-and-seek in a new place? It’s much harder than playing at home. You only know the obvious hiding spots: under the bed, in the closet, behind the couch. The trick is trying to think of hiding spots you can’t even imagine. How do you search in places you never thought could be hiding spots?

That is kind of what scientists like me do when we look for alien life; we’re trying to think of new ways to look for life. In the meantime, we’re looking for life by looking for life like us because that’s what we can imagine.

Looking nearby

The closest place to look for extraterrestrial life is on planets within our solar system.

NASA’s Viking 1 mission began orbiting Earth’s neighbor Mars back in 1976. Looking for life on Mars was one of the most important scientific questions for the mission. The spacecraft included a lander that could go to the planet’s surface to see if there were any life-forms in the dirt there.

A view of the soil on the surface of Mars, as taken by Viking 1 lander on Aug. 1, 1976. NASA/JPL , CC BY

Scientists knew that life on Mars could be really different from life on Earth, so they didn’t look for specific life-forms or molecules. Instead, they tried to design experiments to look for what life does, rather than what it makes.

For example, plants and some other life-forms on Earth do photosynthesis , a process that uses sunlight and carbon dioxide in the air to gather energy and grow. The Viking 1 scientists designed the lander to look for signs of photosynthesis happening on Mars.

To do that, the lander scooped up some dirt, shined a light on it and made measurements to see if any of the carbon dioxide in the air was transferred into the dirt. This experiment did not show any signs of photosynthesis in Mars’ dirt.

The lander had two other experiments that looked for evidence of organisms growing in the dirt on Mars. One used carbon dioxide gas and another one used sugar and amino acid molecules that life-forms on Earth like to eat.

The combination of these three experiments and other measurements led most scientists to agree that there probably is not life on the surface of Mars, at least life that does something like photosynthesis or eats sugar. But we still don’t know if there are signs of ancient life-forms on Mars, or even current life deep below the surface.

The Viking lander experiments were the most direct tests for life on other planets. In terms of a game of hide-and-seek, though, these experiments were basically like looking in the closet: It’s a pretty obvious hiding spot, but you should check there just in case. Even so, it took scientists a long time to interpret the results.

At four light-years away, Proxima Centauri is the star closest to our Sun – could one of its planets host life? ESA/Hubble & NASA , CC BY

Looking far away

Looking for life outside the solar system is even harder and requires different techniques.

The closest exoplanet – a planet orbiting a star that is not our Sun – is Proxima Centauri b , and it’s more than 2 million, million miles (that’s 2 followed by 13 zeros) away from Earth. These distant worlds are so far away that scientists are not going to send landers to do experiments on them for a long time.

Looking for life on exoplanets is kind of like trying to play hide-and-seek in your neighbor’s house, but you only get to look through the windows and can’t go inside. You might get lucky and get just the right angle to spot someone hiding, but you can’t know all the spots you’re not able to see.

Tools like the new James Webb Space Telescope can reveal the size of exoplanets, how close they are to their stars, and maybe the gases in their atmospheres. But that’s it. How would you look for life with that?

Because elements emit light at particular wavelengths, scientists can determine what a distant planet’s atmosphere is made up of based on its spectra. JPL , CC BY

Astronomers have thought about looking for life on exoplanets by looking for oxygen . They started with this strategy because on Earth, life-forms made most of the oxygen in our atmosphere. Maybe oxygen on another planet was made by alien life.

We’ve learned, though, that there are other ways to make oxygen that don’t involve life. So now, astronomers don’t look for just oxygen – instead they’re on the hunt for a planet that has oxygen along with water and other gases, like methane and carbon dioxide. Together, these combinations might indicate life because we don’t think planets without life would have them. But we’re still uncertain about that, too!

Looking for life by looking for these gases is kind of like looking behind the couch in our hide-and-seek game. Do we know anyone is going to be there? No. But we only get to look through the windows, and we can imagine people hiding behind couches. We might as well try – where else would we even look?

What game are we playing?

There are two big differences between playing hide-and-seek and looking for aliens.

First, when you’re playing hide-and-seek, you usually know that you’re playing with someone else. We have no idea if there are aliens out there to find! It’s possible there’s no other life out there, and it’s possible there are aliens right next door. Until we find examples of life besides our own, we won’t know how common life is in the universe.

No sign so far of an alien civilization nearby. janiecbros/E+ via Getty Images

The second difference is that most scientists don’t think alien life is hiding from us ; it’s just that we haven’t spotted it yet. There are some ideas that more advanced civilizations might avoid being detected , but researchers don’t think that’s happening in our solar system.

Most astronomers and astrobiologists know that if we only look for life that’s like Earth life, we might miss the signs of aliens that are really different. But honestly, we’ve never detected aliens before, so it’s hard to know where to start. When you don’t know what to do, starting somewhere is usually better than nowhere.

Looking for life using experiments like the Viking lander or searching for oxygen might not help. But we might get lucky. And even if we’re not, we’ll get to cross a couple of obvious possibilities off the list. Then we can focus on the harder question of imagining something we’ve never thought of before.

Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to [email protected] . Please tell us your name, age and the city where you live.

Cole Mathis , Assistant Professor of Complex Adaptive Systems, Arizona State University

This article is republished from The Conversation under a Creative Commons license. Read the original article .

Stories Chosen For You

Should trump be allowed to run for office, how do i keep my fruit, veggies and herbs fresh longer.

We all know fresh produce is good for us , but fruit, vegetables and herbs have a tendency to perish quickly if left uneaten.

This is because even after harvesting , produce from living plants tends to continue its biological processes. This includes respiration: producing energy from stored carbohydrates, proteins and fats while releasing carbon dioxide and water vapour. (Ever found a sprouting potato in your pantry?)

On top of that, fresh produce also spoils easily thanks to various microbes – both harmless and ones that can cause disease, called pathogens.

Simply chucking things in the fridge won’t solve the problem, as different types of plants will react differently to how they’re stored. So, how can you combat food waste and keep produce fresh for longer? Fortunately, there are some helpful tips.

Freshness and quality begin at the farm

Farmers always aim to harvest produce when it’s at an optimal condition, but both pre-harvest and post-harvest factors will affect freshness and quality even before you buy it.

Pre-harvest factors are agricultural, such as climatic conditions, soil type and water availability. Post-harvest factors include washing and cleaning after harvesting, transportation and distribution, processing and packaging, and storage.

As consumers we can’t directly control these factors – sometimes the veggies we buy just won’t be as good. But we can look out for things that will affect the produce once we bring it home.

One major thing to look out for is bruised, wounded or damaged produce. This can happen at any stage of post-harvest handling, and can really speed up the decay of your veggies and fruit .

Moisture loss through damaged skin speeds up deterioration and nutrient loss. The damage also makes it easier for spoilage microbes to get in.

To wash or not to wash?

You don’t need to wash your produce before storing it. A lot of what we buy has already been washed commercially. In fact, if you wash your produce and can’t get it completely dry, the added moisture could speed up decay in the fridge.

But washing produce just before you use it is important to remove dirt and pathogenic bugs.

Don’t use vinegar in your washing water despite what you see on social media. Studies indicate vinegar has no effect on lowering microbial loads on fresh produce.

Similarly, don’t use baking soda. Even though there’s some evidence baking soda can remove pesticide residues from the surface of some produce, it’s not advisable at home. Just use plain tap water.

Location, location, location

The main thing you need is the correct type of packaging and the correct location – you want to manage moisture loss, decay and ripening.

The three main storage options are on the counter, in the fridge, or in a “cool, dry and dark place”, such as the pantry. Here are some common examples of produce and where best to put them.

Bananas, onion, garlic, potatoes, sweet potato and whole pumpkin will do better in a dark pantry or cupboard. Don’t store potatoes and onions together: onions produce a gas called ethylene that makes potatoes spoil quicker, while the high moisture in potatoes spoils onions.

In fact, don’t store fruits such as apples, pears, avocado and bananas together, because these fruits release ethylene gas as they ripen, making nearby fruits ripen (and potentially spoil) much faster. That is, unless you do want to ripen your fruits fast.

All leafy greens, carrots, cucumbers, cauliflower and broccoli will do best in the low-humidity drawer (crisper) in the fridge. You can put them in perforated plastic bags to retain moisture but maintain air flow. But don’t put them in completely sealed bags because this can slow down ripening while trapping carbon dioxide , leading to decay and bad smells.

Some fruits will also do best in the fridge. For example, apples and citrus fruits such as oranges can keep fresh longer in the fridge (crisper drawer), although they can stay at room temperature for short periods. However, don’t store watermelon in the fridge for too long, as it will lose its flavour and deep red colour if kept refrigerated for longer than three days .

Most herbs and some leafy vegetables – like celery, spring onions and asparagus – can be kept with stems in water to keep them crisp. Keep them in a well-ventilated area and away from direct sunlight, so they don’t get too warm and wilt.

Experimenting at home is a good way to find the best ways to store your produce.

Fight food waste and experiment

Don’t buy too much. Whenever possible, buy only small amounts so that you don’t need to worry about keeping them fresh. Never buy bruised, wounded or damaged produce if you plan to keep it around for more than a day.

“Process” your veggies for storage. If you do buy a large quantity – maybe a bulk option was on sale – consider turning the produce into something you can keep for longer. For example, banana puree made from really ripe bananas can be stored for up to 14 days at 4°C . You can use freezing, blanching, fermentation and canning for most vegetables.

Consider vacuum sealing. Vacuum packaging of vegetables and berries can keep them fresh longer, as well. For example, vacuum-sealed beans can keep up to 16 months in the fridge, but will last only about four weeks in the fridge unsealed .

Keep track. Arrange your fridge so you can see the produce easily and use it all before it loses freshness.

Experiment with storage hacks. Social media is full of tips and hacks on how best to store produce. Turn your kitchen into a lab and try out any tips you’re curious about – they might just work. You can even use these experiments as a way to teach your kids about the importance of reducing food waste.

Senaka Ranadheera , Associate Professor, The University of Melbourne

Tonga’s volcanic eruption could cause unusual weather for the rest of the decade

Hunga Tonga-Hunga Ha’apai (Hunga Tonga for short) erupted on January 15 2022 in the Pacific Kingdom of Tonga. It created a tsunami which triggered warnings across the entire Pacific basin , and sent sound waves around the globe multiple times.

A new study published in the Journal of Climate explores the climate impacts of this eruption.

Our findings show the volcano can explain last year’s extraordinarily large ozone hole, as well as the much wetter than expected summer of 2024.

The eruption could have lingering effects on our winter weather for years to come.

A cooling smoke cloud

Usually, the smoke of a volcano – and in particular the sulphur dioxide contained inside the smoke cloud – ultimately leads to a cooling of Earth’s surface for a short period.

This is because the sulphur dioxide transforms into sulphate aerosols, which send sunlight back into space before it reaches the surface. This shading effect means the surface cools down for a while, until the sulphate falls back down to the surface or gets rained out.

This is not what happened for Hunga Tonga.

Because it was an underwater volcano, Hunga Tonga produced little smoke, but a lot of water vapour: 100–150 million tonnes, or the equivalent of 60,000 Olympic swimming pools . The enormous heat of the eruption transformed huge amounts of sea water into steam, which then shot high into the atmosphere with the force of the eruption.

Animation of the Hunga Tonga eruption recorded on January 15 2022 by Japan’s Himawari-8 weather satellite. The plume is just under 500km across. Japan Meteorological Agency , CC BY

All that water ended up in the stratosphere: a layer of the atmosphere between about 15 and 40 kilometres above the surface, which produces neither clouds nor rain because it is too dry.

Water vapour in the stratosphere has two main effects. One, it helps in the chemical reactions which destroy the ozone layer, and two, it is a very potent greenhouse gas.

There is no precedent in our observations of volcanic eruptions to know what all that water would do to our climate, and for how long. This is because the only way to measure water vapor in the entire stratosphere is via satellites. These only exist since 1979, and there hasn’t been an eruption similar to Hunga Tonga in that time.

Follow the vapor

Experts in stratospheric science around the world started examining satellite observations from the first day of the eruption. Some studies focused on the more traditional effects of volcanic eruptions, such as the amount of sulphate aerosols and their evolution after the eruption , some concentrated on the possible effects of the water vapour , and some included both .

But nobody really knew how the water vapor in the stratosphere would behave. How long will it remain in the stratosphere? Where will it go? And, most importantly, what does this mean for the climate while the water vapour is still there?

Those were exactly the questions we set off to answer.

We wanted to find out about the future, and unfortunately it is impossible to measure that. This is why we turned to climate models, which are specifically made to look into the future.

We did two simulations with the same climate model. In one, we assumed no volcano erupted, while in the other one we manually added the 60,000 Olympic swimming pools worth of water vapor to the stratosphere. Then, we compared the two simulations, knowing that any differences must be due to the added water vapor.

The ash plume from the Hunga Tonga eruption in an image taken by an astronaut on January 16 2022 from the International Space Station. NASA

What did we find out?

The large ozone hole from August to December 2023 was at least in part due to Hunga Tonga. Our simulations predicted that ozone hole almost two years in advance.

Notably, this was the only year we would expect any influence of the volcanic eruption on the ozone hole. By then, the water vapour had just enough time to reach the polar stratosphere over Antarctica, and during any later years there will not be enough water vapour left to enlarge the ozone hole.

As the ozone hole lasted until late December, with it came a positive phase of the Southern Annular Mode during the summer of 2024. For Australia this meant a higher chance of a wet summer, which was exactly opposite what most people expected with the declared El Niño. Again, our model predicted this two years ahead.

In terms of global mean temperatures, which are a measure of how much climate change we are experiencing, the impact of Hunga Tonga is very small, only about 0.015 degrees Celsius. (This was independently confirmed by another study .) This means that the incredibly high temperatures we have measured for about a year now cannot be attributed to the Hunga Tonga eruption.

Disruption for the rest of the decade

But there are some surprising, lasting impacts in some regions of the planet.

For the northern half of Australia, our model predicts colder and wetter than usual winters up to about 2029. For North America, it predicts warmer than usual winters, while for Scandinavia, it again predicts colder than usual winters.

The volcano seems to change the way some waves travel through the atmosphere. And atmospheric waves are responsible for highs and lows, which directly influence our weather.

It is important here to clarify that this is only one study, and one particular way of investigating what impact the Hunga Tonga eruption might have on our weather and climate. Like any other climate model, ours is not perfect.

We also didn’t include any other effects, such as the El Niño–La Niña cycle. But we hope that our study will stir scientific interest to try and understand what such a large amount of water vapour in the stratosphere might mean for our climate.

Martin Jucker , Lecturer in Atmospheric Dynamics, UNSW Sydney

'Help me': George Conway hits out as MAGA aims 'vile' attacks at his daughter

Conservative attorney and Never Trump activist George Conway has a fiery message for the people he says are going after his daughter.

"I don't make personal requests on here often, if ever. But Laura Loomer (whom Trump apparently wanted to hire), along with an online mob of other Trump/MAGA supporters, have been attacking @claudiamcomwayy in the most vile of terms, simply because she noted that Donald Trump is a convicted felon," said he said on X.

He was writing in reponse to another account that called attention to the abuse. He added that he would like others to "help me report these vile people, and please let these vile people know what you think."

According to Newsweek, Claudia Conway "made a return to X, formerly Twitter , after a monthslong absence to weigh in on the presumptive GOP presidential nominee last week being found guilty on all 34 counts in his criminal hush money trial.

After her mother praised Trump, calling him 'resilient and a fighter,' Claudia Conway responded in a since-deleted post and wrote: 'I think you forgot to add 'felon.''"

George Conway is divorced from his wife Kellyanne Conway, who served as a White House strategist for Trump.

ALSO READ: Marjorie Taylor Greene: Ilhan Omar is ‘lucky’ to be in America

Their daughter's post was followed by attacks from MAGA supporters. In one of the most prominent cases, far-right influencer Laura Loomer responded to her, calling her a "low IQ, highly sexually promiscuous woman with daddy issues" and criticizing her for having a deal with Playboy.

Loomer, who describes herself as a "Proud Islamophobe" and has defended white nationalism, has run multiple unsuccessful campaigns for Congress. Trump reportedly considered her for a position on his campaign until his aides talked him out of it . Even far-right Rep. Marjorie Taylor Greene (R-GA) publicly criticized Trump for considering giving her a role.

Trump, following his conviction in the Manhattan case, is scheduled to be sentenced on July 11.

‘Journalistic dystopian nightmare’: Inside a Tennessee college media meltdown

Michael cohen, red finch and the fateful moment trump lost the jury, justice delayed is not always justice denied.

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NASA discovers potentially habitable exoplanet 40 light years from Earth

Nasa says that gliese 12 b, about 40 light years away, could help researchers understand the habitability of other planets across the galaxy.

NASA announced the discovery of a planet 40 light years from Earth that orbits every 12.8 days and is possibly even habitable.

Gliese 12 b is a "super Earth exoplanet" that is nearly the same size as Earth or slightly smaller, according to a NASA news release . Exoplanets are planets outside of our solar system, NASA's website says.

“We’ve found the nearest, transiting, temperate, Earth-size world located to date,” Masayuki Kuzuhara, a project assistant professor at the Astrobiology Center in Tokyo, said in a statement. “Although we don’t yet know whether it possesses an atmosphere, we’ve been thinking of it as an exo-Venus, with similar size and energy received from its star as our planetary neighbor in the solar system.”

The planet orbits a so-called cool red dwarf star called Gliese 12, according to NASA. Gliese 12 is only about 27% of the sun’s size, with about 60% of the sun’s surface temperature, NASA said.

Under the assumption that the planet has no atmosphere, NASA astronomers believe it has a surface temperature of around 107 degrees Fahrenheit.

Red dwarf stars could be key to finding Earth-size planets

The extremely small sizes and masses of red dwarf stars make them ideal for finding Earth-size planets, according to NASA.

"A smaller star means greater dimming for each transit, and a lower mass means an orbiting planet can produce a greater wobble, known as 'reflex motion,' of the star," the agency said. "These effects make smaller planets easier to detect."

The "lower luminosities of red dwarf stars also make it easier to determine if the planets that orbit them are habitable and have liquid water on their surfaces, according to NASA.

NASA researchers 'need more examples like Gliese 12 b'

The distance separating Gliese 12 and Gliese 12 b is just 7% of the distance between Earth and the sun, NASA said. The planet receives 1.6 times more energy from its star than Earth does from the sun.

“Gliese 12 b represents one of the best targets to study whether Earth-size planets orbiting cool stars can retain their atmospheres, a crucial step to advance our understanding of habitability on planets across our galaxy,” Shishir Dholakia, a doctoral student at the Centre for Astrophysics at the University of Southern Queensland in Australia, said in a statement.

Researchers intend to study Gliese 12 b and other similar planets because they could help "unlock some aspects" of our solar system’s evolution, according to NASA.

“We know of only a handful of temperate planets similar to Earth that are both close enough to us and meet other criteria needed for this kind of study, called transmission spectroscopy, using current facilities,” Michael McElwain, a research astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said in a statement. “To better understand the diversity of atmospheres and evolutionary outcomes for these planets, we need more examples like Gliese 12 b.”

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‘Alien Earth’ close to our planet could host life, scientists discover

A rare discovery of a planet 40 light years away could provide crucial answers to questions about life in the Universe.

Image credit: NASA/JPL-Caltech/R. Hurt (Caltech-IPAC)

Humans could now be closer to finding a second home as astronomers have made a rare discovery: a new Earth-sized planet that could support human life.

If the planet has an atmosphere, the scientists think it could also hold water – and maybe, just maybe, even host alien life on its surface.

Published in the Monthly Notices of the Royal Astronomical Society , the new study describes the rocky exoplanet known as Gliese 12 b . It has the same surface temperature as the UK in the 2022 heatwave – a balmy 42ºC (107ºF) – making it, in theory, habitable.

While it’s still much higher than Earth’s typical surface temperature of 15º C (59º F), Gliese 12 b's climate is still considered unusually cold – it’s one of the chilliest of the 5,000 exoplanets confirmed so far.

Gliese 12 b was discovered by an international team of scientists alongside NASA and ESA.

“This is a really exciting discovery and will help our research into planets similar to Earth across our Galaxy. Thrillingly, this planet is the closest Earth-sized and temperature planet we know,” one of the scientists, University of Warwick astrophysicist Dr Thomas Wilson , said.

“Planets like Gliese 12 b are very few and far between, so for us to be able to examine one this closely and learn about its atmosphere and temperature is very rare.”

Wilson and the team discovered the planet 40 light years away, in the constellation of Pisces orbiting a cool red dwarf star called Gliese 12. That’s the planet’s equivalent of our Sun , except Gliese 12 is only 27 per cent the size of ours and has 60 per cent its surface temperature.

The planet is similar in size to Earth (though slightly closer to Venus in size), and orbits its star every 12.8 days – a much shorter ‘year’ than our 365 days.

So what does ‘habitable’ actually mean? Being habitable means that it’s possible humans could survive on a planet. But the scientists still don’t know whether Gliese 12 b has an atmosphere, and what the atmosphere could be made of if it does.

Answering this question will be the researchers’ next step – and the result would be crucial in unlocking information about atmospheres in our own Solar System. In particular, the researchers want to find out why Earth’s and Venus’s are so different: Venus was made inhabitable when accelerated climate change destroyed the planet’s water sources.

Gliese 12 b’s atmosphere, if it has one, could explain why such changes happen – and predict what might happen to the Earth’s. And, if it does have an atmosphere, this would mean it can maintain its temperatures and allow the presence of liquid water.

The rare conditions of Gliese 12 b make it a good future candidate for the James Webb Space Telescope – and therefore, hopefully, answer some more questions.

• The 4 biggest questions about alien life, answered by an astrobiologist
• What does it mean if an exoplanet is 'habitable'?
• The Dark Universe: Why we're about to solve the biggest mystery in science

Share this article

News editor, BBC Science Focus

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Why do astronomers look for signs of life on other planets based on what life is like on Earth?

Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to [email protected] .

Why do astronomers look for signs of life on other planets based on how life is on Earth? Couldn’t there be totally different kinds of life on other planets? – Henry, age 13, Somerville, Massachusetts

Have you ever played hide-and-seek in a new place? It’s much harder than playing at home. You only know the obvious hiding spots: under the bed, in the closet, behind the couch. The trick is trying to think of hiding spots you can’t even imagine. How do you search in places you never thought could be hiding spots?

That is kind of what scientists like me do when we look for alien life; we’re trying to think of new ways to look for life. In the meantime, we’re looking for life by looking for life like us because that’s what we can imagine.

Looking nearby

The closest place to look for extraterrestrial life is on planets within our solar system.

NASA’s Viking 1 mission began orbiting Earth’s neighbor Mars back in 1976. Looking for life on Mars was one of the most important scientific questions for the mission. The spacecraft included a lander that could go to the planet’s surface to see if there were any life-forms in the dirt there.

Scientists knew that life on Mars could be really different from life on Earth, so they didn’t look for specific life-forms or molecules. Instead, they tried to design experiments to look for what life does, rather than what it makes.

For example, plants and some other life-forms on Earth do photosynthesis , a process that uses sunlight and carbon dioxide in the air to gather energy and grow. The Viking 1 scientists designed the lander to look for signs of photosynthesis happening on Mars.

To do that, the lander scooped up some dirt, shined a light on it and made measurements to see if any of the carbon dioxide in the air was transferred into the dirt. This experiment did not show any signs of photosynthesis in Mars’ dirt.

The lander had two other experiments that looked for evidence of organisms growing in the dirt on Mars. One used carbon dioxide gas and another one used sugar and amino acid molecules that life-forms on Earth like to eat.

The combination of these three experiments and other measurements led most scientists to agree that there probably is not life on the surface of Mars, at least life that does something like photosynthesis or eats sugar. But we still don’t know if there are signs of ancient life-forms on Mars, or even current life deep below the surface.

The Viking lander experiments were the most direct tests for life on other planets. In terms of a game of hide-and-seek, though, these experiments were basically like looking in the closet: It’s a pretty obvious hiding spot, but you should check there just in case. Even so, it took scientists a long time to interpret the results.

Looking far away

Looking for life outside the solar system is even harder and requires different techniques.

The closest exoplanet – a planet orbiting a star that is not our Sun – is Proxima Centauri b , and it’s more than 2 million, million miles (that’s 2 followed by 13 zeros) away from Earth. These distant worlds are so far away that scientists are not going to send landers to do experiments on them for a long time.

Looking for life on exoplanets is kind of like trying to play hide-and-seek in your neighbor’s house, but you only get to look through the windows and can’t go inside. You might get lucky and get just the right angle to spot someone hiding, but you can’t know all the spots you’re not able to see.

Tools like the new James Webb Space Telescope can reveal the size of exoplanets, how close they are to their stars, and maybe the gases in their atmospheres. But that’s it. How would you look for life with that?

Astronomers have thought about looking for life on exoplanets by looking for oxygen . They started with this strategy because on Earth, life-forms made most of the oxygen in our atmosphere. Maybe oxygen on another planet was made by alien life.

We’ve learned, though, that there are other ways to make oxygen that don’t involve life. So now, astronomers don’t look for just oxygen – instead they’re on the hunt for a planet that has oxygen along with water and other gases, like methane and carbon dioxide. Together, these combinations might indicate life because we don’t think planets without life would have them. But we’re still uncertain about that, too!

Looking for life by looking for these gases is kind of like looking behind the couch in our hide-and-seek game. Do we know anyone is going to be there? No. But we only get to look through the windows, and we can imagine people hiding behind couches. We might as well try – where else would we even look?

What game are we playing?

There are two big differences between playing hide-and-seek and looking for aliens.

First, when you’re playing hide-and-seek, you usually know that you’re playing with someone else. We have no idea if there are aliens out there to find! It’s possible there’s no other life out there, and it’s possible there are aliens right next door. Until we find examples of life besides our own, we won’t know how common life is in the universe.

The second difference is that most scientists don’t think alien life is hiding from us ; it’s just that we haven’t spotted it yet. There are some ideas that more advanced civilizations might avoid being detected , but researchers don’t think that’s happening in our solar system.

Most astronomers and astrobiologists know that if we only look for life that’s like Earth life, we might miss the signs of aliens that are really different. But honestly, we’ve never detected aliens before, so it’s hard to know where to start. When you don’t know what to do, starting somewhere is usually better than nowhere.

Looking for life using experiments like the Viking lander or searching for oxygen might not help. But we might get lucky. And even if we’re not, we’ll get to cross a couple of obvious possibilities off the list. Then we can focus on the harder question of imagining something we’ve never thought of before.

Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to [email protected] . Please tell us your name, age and the city where you live.

And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.

This article is republished from The Conversation , a nonprofit, independent news organization bringing you facts and analysis to help you make sense of our complex world.

It was written by: Cole Mathis , Arizona State University .

What happens if someone dies in space?

Could a telescope ever see the beginning of time? An astronomer explains

Cole Mathis has previously received funding from the NASA Postdoctoral Program.

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