How many planets have we discovered that can support human life?

How many planets have we discovered that can support human life?

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I have heard a lot of buzz about distant planets that could potentially be second homes for human existence, but what is that approximate number?

There is currently only one planet known to be capable of supporting human life, and you're on it.

Several planets have been found in the region in which we expect water to be liquid on much of the planet. Of these, only one fits the criteria of being Earth-sized and well placed in the habitable zone: Kepler 186-f

However we know nothing about it's atmosphere (or lack of one). The star is a red dwarf, so it could be subject to dramatic solar flares. The planet is rather colder than earth, so could be in a perpetual "snowball world" state, depending on the composition of the atmosphere and the strength of the greenhouse effect. The atmosphere would be very unlikely to be even close to breathable, and it is nearly 500 light-years from Earth, so could not be reached in a reasonable amount of time, even with much more advanced propulsion.

At the moment we can't usually detect most Earth-like planets in the habitable zone of brighter stars like the sun, though the probably do exist and may be common.

You may be interested in the number of habitable zone planets. These are planetary-mass objects in a sort of "Goldilocks" region from their respective stars: This region is just right, given adequate atmospheric conditions, to possibly permit the existence of liquid water on the surface. That's not a surefire sign that the planet is capable of supporting humans, but it's certainly a good start.

Scientists Kane and Gellino have tabulated such information at the HZ Gallery. As of Sep 2015, the site assesses nearly 1600 exoplanets of which 62 spend their time entirely within the habitable zone.

How many planets can support life like Earth?

Zooming in on our odds of finding a hospitable planet.

Astronomers’ cups have runneth over with alien worlds since NASA launched its (now retired) ­exoplanet-​­hunting ­Kepler space telescope in 2009. But sussing out which orbiting rocks could support life as we know it isn’t an exact science our current deep-space-searching technology can’t peer closely enough to determine surface and atmospheric compositions on faraway places. Here’s what experts have managed to work out so far.

1. Confirmed planets
Orbiting bodies dim starlight as they pass in front of their respective suns, which makes the fireballs appear to flicker out at regular intervals from our perspective. Astronomers think they’ve already spotted potentially telltale winks from more than 8,000 planets but have confirmed the existence of only around half that number.

2. Rocky planets
Mass really does matter. Rocks much smaller than ours lack the gravity to hold an atmosphere, so liquid surface water won’t stick around. Anything twice our size or larger is likely to gather dust, gas, and ice, creating a barren world like Jupiter or Neptune. Orbs 0.8 to 1.5 times Earth’s radius can be both rocky and wet, and we’ve found around 1,000 of them.

3. Habitable-zone planets
Life is a Goldilocks game too close to the sun and you roast, too far and you freeze. A few dozen worlds seem to spin in an orbit that’s just right. They could receive anywhere from half to double the radiation that hammers Earth and still harbor life, but factors like how often host stars spit plasma flares could eliminate many contenders.

4. Earth-like planets
Headlines oft herald worlds as “Earth-like,” and a couple dozen could be. But we can’t yet tell whether bodies in other star systems share crucial atmospheric similarities with our home. The closest of our planetary twins is Proxima Centauri b, roughly 4 light-years away. Current probes and scopes can’t gather the intel we need at that distance—yet.

This story originally published in the Out There issue of Popular Science.

Sara Chodoshis an associate editor at PopSci where she writes about everything from vaccine hesitancy to extreme animal sex. She got her master's degree in science journalism at NYU's Science Health and Environmental Reporting Program, and is getting a second master's in data visualization from the University of Girona. Contact the author here.

NASA discovers 715 new planets, including four that could host life

The newly discovered planets were all found in multi-planet systems and most are relatively small. Scientists found planets - all of which orbit 305 stars, making up what are known as planetary systems - when they were analyzing the observational data obtained by NASA’s Kepler space telescope.

We’ve almost doubled today the number of planets known to humanity,” Jack Lissauer, a NASA planetary scientist, said Tuesday during a press conference with reporters.

Kepler was first launched in 2009 and spent four years waiting to see what bodies would float by when the telescope was pointed at 160,000 target stars.

For Kepler to discover a new planet it must be perfectly aligned with a star in the telescope’s view, something that is made especially difficult by the fact that planets orbiting a greater distance from their parent star are far less likely to be found. When a planet and star do successfully align with the telescope it is known as a “transit.”

NASA’s announcement became even more exciting when the researchers said that at least four of the planets, the same ones that are roughly 4.5 times larger than Earth, exist in orbits that are within a star’s habitable zone, or the “Goldilocks zone.” At such a distance these planes could host liquid water and, potentially, life.

The announcement Tuesday covered only the first two years of Kepler’s study, an indication that the existence of many more planets could be announced in the future.

We’ve been able to open the bottleneck to access the mother lode and deliver to you more than 20 times as many planets as had ever been found and announced at once,” Lissauer said. “Although we’ve gotten the big numbers this time, when we have a full four years of Kepler data that will have more planets in the habitable zone. We need more transits.”

The jump in discoveries can be attributed to a new verification technique that NASA uses to examine potential planetary systems rather than individual planets. That method was developed when it occurred to scientists that the vast majority of planets share sibling worlds that orbit a single parent star.

NASA has said that 95-percent of the planets recently discovered by Kepler are smaller than Neptune, which is four-times the size of Earth. Sara Seager, an astronomer at the Massachusetts Institute of Technology, told Reuters that planets of this size are becoming increasingly common throughout the galaxy, at least in terms of humans being aware of them.

Literally, wherever (Kepler) can see them, it finds them,” she said. “That’s why we have confidence that there will be planets like Earth in other places.”

Study Says 40 Billion Planets In Our Galaxy Could Support Life

A new study in the Proceedings of the National Academy of Sciences finds that roughly 1 in 5 stars, like our own sun, have an Earth-like planet orbiting around it. That's about 40 billion planets that could support life in the Milky Way galaxy. Melissa Block talks to co-author Geoff Marcy, an astronomy professor at the University of California-Berkeley, about the latest numbers.

As China and India race to Mars, we'll venture outside our solar system and consider this mind-expanding possibility: There could be 40 billion planets in our Milky Way galaxy that are orbiting stars in a habitable zone that could support life - 40 billion. Makes you kind of puny, doesn't it?

That number of potentially life-supporting planets comes from a new study of data sent back from NASA's Kepler space telescope, data that make the co-author of the new study, Geoff Marcy, feel a little tingly, as he puts it. Marcy is an astronomer at the University of California, Berkeley, and he joins me now. Geoff Marcy, just a little bit tingly, not a lot?

GEOFFREY MARCY: Well, the hairs are standing up on the back of my neck right now. It's really an extraordinary moment for all of us on planet Earth here.

BLOCK: Well, when you're looking for habitable - potentially habitable - planets, what are you looking for? What in particular are you trying to find in the data from the telescope?

MARCY: Well, there are a few properties of a planet that render it suitable for life. One is it ought to have a rocky surface so that the water, if any, on that planet, would puddle into ponds and lakes and oceans. Water, of course, being the important cocktail mixer for organic molecules, allowing them to recombine into amino acids and proteins of which our body is made.

Another key attribute of a habitable world would be its temperature. It can't be so cold that the water is frozen into ice nor so hot that the water would be in the form of steam. But instead we want, of course, liquid water so that the water can do its job as the cocktail mixer of life.

BLOCK: Now in terms of the planets that you think you have identified - maybe 40 billion if you extrapolate out from the data you have - is there any way of knowing how many would be the small, Earth-sized, rocky planet?

It's - we really have no idea. If I had to guess, I'd say something like a fifth of them, maybe a tenth.

I mean, that's still - we're still talking four billion planets.

MARCY: There's plenty to go around.

BLOCK: And the nearest of these potentially habitable planets, how close is the closest one to us?

MARCY: The closest habitable planet might be about 12 light years away. That's a stone's throw in the cosmic sense.

BLOCK: In the cosmic sense. Well, put it in some context in terms of our own solar system.

MARCY: You know, the Voyager spacecraft that we sent out in the 1980s has just now left our solar system. And at the speed it travels, to go to the nearest star, Alpha Centauri, would take something like 700,000 years. So that's really too long to pop over and borrow a cup of sugar.

BLOCK: Is there any danger, do you think, of overselling numbers like this?

MARCY: There is. We have actually no evidence at all of any life, even simple single-celled life. So the next generation of scientists has their work cut out for them to determine if life is actually out there, how common it is and especially whether there's any kindred spirits technologically out there.

BLOCK: Geoffrey Marcy is a professor of astronomy at the University of California, Berkeley. We were talking about the article he co-authored titled, "Prevalence of Earth-sized planets orbiting Sun-like stars." Professor Marcy, thanks so much.

Copyright © 2013 NPR. All rights reserved. Visit our website terms of use and permissions pages at for further information.

NPR transcripts are created on a rush deadline by Verb8tm, Inc., an NPR contractor, and produced using a proprietary transcription process developed with NPR. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR&rsquos programming is the audio record.

Scientists find 3 Earth-sized planets that may support life

Scientists have found three planets about the size of Earth that may be able to support life.

The planets orbit an "ultracool dwarf," a star much smaller and cooler than the sun, but still possibly warm enough to allow for liquid water on the surfaces of at least two of the planets.

The planets have a "winning combination" of being Earth-sized, potentially habitable and well-suited for atmospheric studies, making them "the first opportunities to find chemical traces of life outside our solar system," study co-author Julien de Wit told CNBC in an email.

The team published its findings Monday in the peer-reviewed journal Nature.

This is the first time planets have been observed orbiting ultra-cool dwarves — though scientists had suspected that such stars could host small solar systems.

The researchers note in their paper that "there should be a large but hitherto undetected population of terrestrial planets orbiting" ultra-cool dwarves, "ranging from metal-rich Mercury-sized planets to more hospitable, volatile-rich, Earth-sized planets."

The team found the planets using the Trappist telescope, an optical system located in Chile but operated robotically from a control center in Belgium.

David Kipping, an astronomer at Columbia University who was not involved with the research, told the New Scientist that there "is a legitimate case to be made that this system could host life, and we may be able to infer the presence of that life in the next decade."

But not everyone is convinced the planets are habitable.

San Diego State University astronomer Jerome Orosz, told KPBS that two of the planets receive two to four times the amount of radiation Earth does, which "seems high."

What are the Chances?

But do aliens actually exist? We don't have any direct evidence one way or the other[36], but an absence of evidence isn't necessarily evidence of absence. That depends upon how likely it is that we would find evidence of extraterrestrials if they exist.

Whether or not you think aliens exist depends upon what assumptions about the origin of life you bring to the question. The relevant assumptions were organized into an equation by pioneer SETI researcher Frank Drake (as Jill Tarter says, 'An equation is nothing more than a lovely way to organize our ignorance'[37]). The Drake Equation, as it has become known, suggests that the number of detectable civilizations (N) is determined by multiplying:

the rate of formation of stars suitable for life (R*)
the fraction of those with planets (fp)
the number of those planets that are suitable for life (ne)
the fraction of these planets where life actually evolves (fl)
the fraction of these on which intelligent life evolves (fi)
the fraction of these that develop civilizations that produce detectable signs of their existence (fc)
the length of time in which such civilizations will produce detectable signs of their existence (L)

N = R* x fp x ne x fl x fi x fc x L

The value of N (number of detectable civilizations) derived from this equation depends more upon the philosophical assumptions underlying the values assigned to its component parts than it does to hard scientific evidence. For atheists, the answer mainly depends upon how likely the evolution of sentient life by purely natural processes is (ie upon the value of fl x fi). As evolutionary biologist Paul Ewald writes, 'if there is life on other planets, natural selection has to be the fundamental organizing principle there, too.'[38] While I think a Christian can accept evolution by natural selection as God's way of populating creation, there can be no 'has to be' about it for anyone who believes in God, and there are a range of other options that Christians should seriously consider.[39]

The more we learn about the structure of life, the less likely it seems that life could be the result of purely natural processes (whether or not those processes were designed by God).[40] Stephen C Meyer calculates that 'the probability of constructing a rather short, function protein at random [is] so small as to be effectively zero (no more than 1 chance in 10125), even given our multi-billion-year-old universe.'[41] To put this figure in context, there are only 1065 atoms in our entire galaxy! Such a staggeringly improbable explanation is the only one available given naturalistic assumptions.

Christian astronomer Dr Hugh Ross argues that there are at least 26 characteristics of the universe and 33 characteristics of our galaxy, solar system, and planet that are finely tuned for life. He estimates that the probability of all 59 factors coming together by natural processes alone are 1053 to 1 (10000000000000000000000000000000000
0000000000000000000 to 1)! A liberal estimate of how many planets may exist (though we have only documented about 40, none life-bearing) is 1022 (10000000000000000000000). Combining these two probabilities tells us that the odds of there being just one life sustaining planet in the universe, given only the operation of natural causes, is 1031 to 1 against (or 10000000000000000000000000000000 to 1). Therefore, says Ross, by natural processes alone, we shouldn't even be here &ndash let alone alien life forms on another planet.[42]

While atheists have to argue for or against alien life from assumptions based in naturalistic evolution, Christians are free to argue from other premises. For example, philosopher Alvin Plantinga argues that 'it would seem strange if God would have created this entire universe and have creatures in only one small corner who were able to witness it and see what miraculous work he has done. So the natural thing to think from a Christian perspective is that there are lots and lots of intelligent species out there.'

Two billion planets in our galaxy may be suitable for life

Our galaxy probably contains at least two billion planets that, like Earth, have liquid water on their surfaces and orbit around their parent stars in the "habitable zone" for life. The nearest, according to astronomers, could be a mere 12 light years away.

A new study, published on Monday in the Proceedings of the National Academy of Sciences, suggests that Earth-like planets capable of supporting life are far more common than previously thought. Using measurements from Nasa's Kepler space observatory, scientists led by Erik Petigura at the University of California, Berkeley, estimated that 22% of our galaxy's sun-like stars have rocky planets circling them in the zone where they get roughly the same amount of light energy as Earth receives from the sun. There are around 100bn stars in our galaxy, of which 10% are like the sun.

So far Kepler has studied more than 150,000 stars and identified more than 3,000 candidate planets, but many of these are "gas giants", similar to Jupiter, that orbit close to their parent stars. If there is life out there, it is far more likely to have evolved on rocky planets with liquid water on their surfaces, similar to Earth.

To get their results, Petigura's team looked for planets in Kepler data that had a radius up to double that of Earth. They searched for planets that orbited far enough from their star that liquid water would not evaporate, but not so far that the water would all freeze.

Subhanjoy Mohanty, an astrophysicist at Imperial College London who was not involved with the study, said: "This is the first estimate of the frequency of Earth-like planets around sun-like stars, in orbits large enough to lie in the habitable zone of their stars. The finding that roughly one in five sun-like stars may host such planets is an incredibly important one, probably exceeding the expectations of most cautious astronomers."

He added that the latest analysis increased the chances that there might be life somewhere among the stars. "Previous analyses of Kepler data had shown that red dwarfs – the most common type of star in the galaxy, making up about 80% of the stellar population – very frequently harbour Earth-size planets, including in their habitable zones. This new study shows that the same is true around stars more like our own sun. This is certainly an added impetus for planned future missions which will study the atmospheres of these potentially habitable planets, enabling us to investigate whether they are in fact habitable or not, and also whether their atmospheres show actual biosignatures of existing life."

Nasa also announced on Monday that the Kepler probe would be given a new lease of life, following fears that it would have to end its mission after only four years in space. In May 2013, scientists discovered that one of the gyroscopic wheels – known as "reaction wheels" – that kept the probe pointing in the right direction had stopped working and, try as they might, Nasa engineers could not restart it. Unable to point itself at the stars with any accuracy, the probe could no longer be used to collect data about the position of new exoplanets.

But it looks as though there could be a solution that involves reorienting the probe to look along the plane of the galaxy, which will allow it to remain stable with only two of its reaction wheels working. "The old saying 'necessity is the mother of invention' has rung true here, with engineers and scientists from Nasa and the spacecraft manufacturers having figured out this way to – we hope – recover much of the performance we thought we had lost. We are very excited," said Bill Chaplin, an astrophysicist at the University of Birmingham in the UK.

If all goes well, the new Kepler mission – dubbed "K2" – will look for planets around smaller stars than the sun, and will also study the stars themselves. "There are a wealth of fantastically interesting targets for astrophysics that can be observed in the ecliptic plane, which were not accessible in the original Kepler field, notably brighter clusters of stars – where the common origins and distances to these stars make the clusters excellent laboratories for testing our understanding of stars – and young, star-forming regions," said Chaplin.

Scientists discover distant planet which could support life

Scientists have made a “world first” discovery on a distant planet that hosts both water and temperatures which could support life.

Water vapour has been detected on a potentially habitable super-Earth known as K2-18b, located about 110 light years away.

The exoplanet was first spotted in 2015 by Nasa’s Kepler spacecraft but analysis of data has revealed new details that have not been seen on a super-Earth before.

K2-18b is classed as a super-Earth because it is bigger than our Earth — twice as big in fact, as well as eight times heavier.

Current equipment is only able to determine basic factors such as distance, mass and temperature but sophisticated tools developed at University College London have been able to translate existing data from the Hubble Space Telescope to make sense of the unique molecule signatures of water vapour.

K2-18b is too far away for astronomers to see, but they can look at how starlight is filtered through the planet’s atmosphere as it passes around its own sun, called K2-18.

The planet is a lot closer to its star than Earth is to the Sun, meaning it only takes around 33 days to transit.

“It’s the only planet outside our solar system that we know has the correct temperature, an atmosphere and water,” said first author Dr Angelos Tsiaras.

“Of course, K2-18b is not a second Earth, because it is a planet that is much bigger, has a different atmospheric composition. It’s orbiting a completely different star, so it doesn’t look like Earth.

“The search for habitable planets, it’s very exciting, but it’s here to always remind us that this (Earth) is our only home and it’s probably out of the question if we will be able to travel to other planets.”

Although the planet sits in the habitable zone, scientists say that instruments available at present are not able to determine any signs of life.

It will also require many more observations to be sure that it is a habitable planet.

Scientists, who have published their findings in the Nature Astronomy journal after more than a year of work, believe that the water content could be as low as 0.01 per cent or as high as 50 per cent.

“We don’t know how much water there is however, what these models clearly say is that there is an atmosphere and that there is water there,” said co-author Dr Ingo Waldmann.

Researchers do not think K2-18b is the only super-Earth like this and expect to find others with similar characteristics among more than 4,000 exoplanets that have already been discovered.

They hope that newer technology, such as the James Webb Space Telescope due to launch in March 2021, will be able to unlock more secrets beyond our solar system.

“We are looking forward to the next generation of telescopes and go even further,” Dr Tsiaras added.

Co-author Professor Giovanna Tinetti said: “Our discovery makes K2-18b one of the most interesting targets for future study.” – PA

Billions Of Planets Could Support Life

A study released this week found there could be as many as 40 billion habitable planets in the galaxy. Host Rachel Martin talks to Mike Brown, a professor of astronomy at the California Institute of Technology, to help digest the enormity of the finding.

Have you ever gazed out your window on a clear, star-filled night and wondered are we really alone?

MARTIN: Well, there is new science research out there that suggests we may not be after all. The study is based on findings from NASA's Kepler Spacecraft, and it found that there could be as many as 40 billion habitable Earth-sized planets in the galaxy. To help us digest the enormity of this news, we've called up Mike Brown. He is a professor of planetary astronomy at the California Institute of Technology. Thanks so much for being with us.

MIKE BROWN: Oh, thanks for having me.

MARTIN: So, what did you think when you first heard the result of this study this past week? I mean, you deal in this kind of stuff all the time, but was this different?

BROWN: I think even I was a little surprised at just the tremendous number, the incredible likelihood that if you find a star like the Sun that there will be some sort of planet of the size of the Earth around it. That just astounded me.

MARTIN: Even someone like you. You've got maybe a little tingling feeling?

BROWN: I think I did. I think I really did do that thing you say. I went and looked up at the sky and just thought, you know, these things we see up there, there really are other worlds up there.

MARTIN: So, over the last two decades, there have been multiple studies showing similar results that there is likely to be life resembling life on Earth elsewhere in the universe. What does that tell us about our galaxy?

BROWN: I would say that so far we haven't found any evidence that life is likely. I'll keep using the science weasel word, which is life is possible in many places. The problem with life is that the one thing we don't know about life is it easy to start it or is it really hard to start it? And all we know is that it started on Earth. So, there could be 40 billion planets exactly like the Earth in the galaxy and not a single one had life on it, or there could be 40 billion planets like the Earth in the galaxy and every single one of them has life on it.

MARTIN: I mean, unfortunately, there's so much ambiguous language here that's frustrating, I imagine for you too. What does your gut tell you, Mike? The big question: do you think we're alone in the universe?

BROWN: If you have to guess whether life is easy to start or hard to start, I am biased towards easy to start. And I think most people are biased towards easy to start because we live on a planet with life. But you have to realize how biased we are. So, maybe it's not as easy as I think to start that life in the first place.

MARTIN: I think we can still believe.

MARTIN: Mike Brown is a professor of planetary astronomy at Cal Tech. He's also the author of the book "How I Killed Pluto and Why It Had It Coming." He joined us from member station KPCC in Los Angeles. Thanks so much for being with us.

BROWN: Thank you. It was my pleasure.

Copyright © 2013 NPR. All rights reserved. Visit our website terms of use and permissions pages at for further information.

NPR transcripts are created on a rush deadline by Verb8tm, Inc., an NPR contractor, and produced using a proprietary transcription process developed with NPR. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR&rsquos programming is the audio record.

Long haul

Another issue is that astronomers can't agree what conditions are needed for habitability. We only have the Earth to go on but life may also be possible on other types of worlds

It is likely to require a survey of the chemical composition of, perhaps, hundreds of worlds and an understanding of how they are created and evolve, according to Prof Tinetti.

"The Earth really stands out in our own Solar System. It has oxygen, water and ozone. But if we find all that around a planet around a distant star we have to be cautious about saying that it supports life," she said.

"This is why we need to understand not just a handful of planets in the galaxy but hundreds of them. And what we hope is that the habitable planets will stand out, that we will see a big difference between the planets that are habitable and the ones that are not."