Kepler Team Finds System with Two Potentially Habitable Planets

by Nancy Atkinson on April 18, 2013

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The newly discovered planets named Kepler-62e and -f are super-Earths in the habitable zone of a distant sun-like star. The largest planet in the image, Kepler-62f, is farthest from its star and covered by ice. Kepler-62e, in the foreground, is nearer to its star and covered by dense clouds. Closer in orbits a Neptune-size ice giant with another small planet transiting its star. Both habitable-zone planets may be capable of supporting life. Credit: David A. Aguilar (CfA)

The newly discovered planets named Kepler-62e and -f are super-Earths in the habitable zone of a distant sun-like star. The largest planet in the image, Kepler-62f, is farthest from its star and covered by ice. Kepler-62e, in the foreground, is nearer to its star and covered by dense clouds. Closer in orbits a Neptune-size ice giant with another small planet transiting its star. Both habitable-zone planets may be capable of supporting life.
Credit: David A. Aguilar (CfA)

This might be the most exciting exoplanet news yet. An international team of scientists analyzing data from NASA’s Kepler mission has found a planetary system with two small, potentially rocky planets that lie within the habitable zone of their star. The star, Kepler-62, is a bit smaller and cooler than our Sun, and is home to a five-planet system. Two of the worlds, Kepler-62e and Kepler-62f are the smallest exoplanets yet found in a habitable zone, and they might both be covered in water or ice, depending on what kind of atmosphere they might have.

“Imagine looking through a telescope to see another world with life just a few million miles from your own. Or, having the capability to travel between them on a regular basis. I can’t think of a more powerful motivation to become a space-faring society,” said Harvard astronomer Dimitar Sasselov, who is co-author of a new paper describing the discovery.

Masses and sizes for selected planets. The curves show the mass-radius-relation (average density) for different types of planets: The blue line indicates the loci of planets made mostly (75%) of water, the black line that of planets like our Earth that consist almost exclusively of rock (represented here by the mineral Enstatite, MgSiO3, a member of the pyroxite silicate mineral series that makes up most of the Earth's mantle), and so on. The measured radii of Kepler-62e and Kepler-62f plus an estimate of their mass places them in a region (blue areas) where it is highly probable for them to be earth-like planets, that is: planets with a solid (if possibly covered in water) surface. Kepler-11f, on the other hand, is a Mini-Neptune, showing clearly that a comparatively low mass does not necessarily make for a solid planet. Image: L. Kaltenegger (MPIA)

Masses and sizes for selected planets. The curves show the mass-radius-relation (average density) for different types of planets: The blue line indicates the loci of planets made mostly (75%) of water, the black line that of planets like our Earth that consist almost exclusively of rock (represented here by the mineral Enstatite, MgSiO3, a member of the pyroxite silicate mineral series that makes up most of the Earth’s mantle), and so on. The measured radii of Kepler-62e and Kepler-62f plus an estimate of their mass places them in a region (blue areas) where it is highly probable for them to be earth-like planets, that is: planets with a solid (if possibly covered in water) surface. Kepler-11f, on the other hand, is a Mini-Neptune, showing clearly that a comparatively low mass does not necessarily make for a solid planet. Image: L. Kaltenegger (MPIA)

Kepler-62 in the constellation Lyra, and is about 1,200 light-years from Earth.

62e is 1.61 times Earth’s size, circles the star in 122.4 (Earth) days. 62f is 1.4 times the size of Earth, and orbits its star in 267.3 days. Previously, the smallest planet with known radius inside a habitable zone was Kepler-22b, with a radius of 2.4 times that of the Earth.

A third planet in another star system was also announced at a press briefing today. Kepler-69c is 70 percent larger than the size of Earth, and orbits in the habitable zone of a star similar to our Sun. Researchers are uncertain about the composition of Kepler-69c, but astronomer Thomas Barclay from the BAER Institute said its closer orbit of 242 days around a Sun-like star means it is likely more like a super-Venus rather than a super-Earth.

The habitable zone (in which liquid water on a planet's surface can exist) for different types of stars. The inner planets of our Solar System are shown on top, with Earth and Mars in the habitable zone. Kepler-62 is a notably cooler star, and Kepler-62e and -62f are in its habitable zone. For Kepler-69c, another planet announced today by NASA, the error bars for the star's radiation are such that it could possibly in the habitable zone as well. Kepler-22b, the smallest planet found in a habitable zone before the recent discoveries, is very likely a Mini-Neptune, and not a solid planet. In what is denoted the empirical habitable zone, liquid water can exist on the surface of a planet if that planet has sufficient cloud cover. In the narrow habitable zone, liquid water can exist on the surface even without the presence of a cloud cover. Image: L. Kaltenegger (MPIA)

The habitable zone (in which liquid water on a planet’s surface can exist) for different types of stars. The inner planets of our Solar System are shown on top, with Earth and Mars in the habitable zone. Kepler-62 is a notably cooler star, and Kepler-62e and -62f are in its habitable zone. For Kepler-69c, another planet announced today by NASA, the error bars for the star’s radiation are such that it could possibly in the habitable zone as well. Kepler-22b, the smallest planet found in a habitable zone before the recent discoveries, is very likely a Mini-Neptune, and not a solid planet. In what is denoted the empirical habitable zone, liquid water can exist on the surface of a planet if that planet has sufficient cloud cover. In the narrow habitable zone, liquid water can exist on the surface even without the presence of a cloud cover. Image: L. Kaltenegger (MPIA)

The team says that while the sizes of Kepler 62e and 62f are known, their mass and densities are not. However, every planet found in their size range so far has been rocky, like Earth.

Kepler-62 system. Five planets, two of which are in the Habitable Zone. Credit: NASA

Kepler-62 system. Five planets, two of which are in the Habitable Zone. Credit: NASA

“These planets are unlike anything in our solar system. They have endless oceans,” said lead author Lisa Kaltenegger of the Max Planck Institute for Astronomy and the Harvard Smithsonian Center for Astrophysics. “There may be life there, but could it be technology-based like ours? Life on these worlds would be under water with no easy access to metals, to electricity, or fire for metallurgy. Nonetheless, these worlds will still be beautiful blue planets circling an orange star — and maybe life’s inventiveness to get to a technology stage will surprise us.”

As the warmer of the two worlds, Kepler-62e would have a bit more clouds than Earth according to computer models. More distant Kepler-62f would need the greenhouse effect from plenty of carbon dioxide to warm it enough to host an ocean. Otherwise, it might become an ice-covered snowball.

“Kepler-62e probably has a very cloudy sky and is warm and humid all the way to the polar regions. Kepler-62f would be cooler, but still potentially life-friendly,” said Harvard astronomer and co-author Dimitar Sasselov. “The good news is — the two would exhibit distinctly different colors and make our search for signatures of life easier on such planets in the near future. “

The Kepler spacecraft is able to detect planets that transit or cross the face of their host star. Measuring a transit tells astronomers the size of the planet relative to its star.

“All of the other interesting planets in the habitable zone were until now discovered by what is known as the radial velocity method,” said Kaltenegger. “This method gives you a lower limit for the planet’s mass, but no information about its radius. This makes it difficult to assess whether or not a planet is rocky, like the Earth. A small radius (less than 2 Earth radii), on the other hand, is a strong indicator that a planet around is indeed rocky – unless we are talking about a planet around a very young star.”

“What makes Kepler-62e and Kepler-62f so exciting is a combination of two factors,” Kaltenegger added. “We know their radius, which indicates that these are indeed rocky planets, and they orbit their star in the habitable zone. That makes them our best candidates for habitable planets out there yet.

Kaltenegger provides more details on these exoplanets in this video:

Sources: Max Planck Institute for Astronomy, CfA

About 

Nancy Atkinson is Universe Today's Senior Editor. She also is the host of the NASA Lunar Science Institute podcast and works with Astronomy Cast. Nancy is also a NASA/JPL Solar System Ambassador.

Cymagen April 18, 2013 at 7:09 PM

I find this to be quite fascinating and intriguing. It piques my curiosity and enhances my wonderment.

Peter Greyman April 18, 2013 at 7:16 PM

Ok but 1,200 light-years, that’s quite a far away…

Torbjörn Larsson April 18, 2013 at 10:01 PM

Of all concerns voiced on these things, I understand this the least. This work still informs us on astrobiology conditions.

It isn’t as if we had plans to visit there. The main purpose is research.

Sam Juvonen April 18, 2013 at 11:42 PM

Yes, the science is the thing. It’s amazing how much we’ve learned of the solar system and cosmos in the last 10-20 years alone.

I’m extremely sceptical of humans ever leaving our home solar system. The energy budget required is just enormous. I hope I turn out to be wrong and somebody comes up with a warp drive or subspace modulator or detects some convenient wormholes hanging around of course… I just wish I get to see proof of life off-Earth in my lifetime. A permanent research station on the Moon/asteroids/Mars would be nice too :)

Mpj Marsphotojournal April 19, 2013 at 8:55 AM

For now it is sufficient to catalog putative habitable exoplanets as it is in reach of our technological capabilities to date. In the not too far future we will also start to spectroscopically analyze the atmospheres of those planets and look for biogenic tracer gases like methane and in case of technological inteligent exo-life for eg. artificial illumination on the night-sides.
But meanwhile we should advance our knowledge of exo-life in our solar system and 1st finish the Viking life detection experiments on Mars – which could yield some interesting facts about the connection of atmospheric methane as trace gas and life (exo-planets?) and 2nd move on to the outer planets moons which are not located in any definition of a HZ but are still suspected to harbor underground/ice oceans and possibly life. Chances and capabilities are a lot higher that definitive proof of exo-life – during our life-times – will be found in our system rather than other solar systems.

Torbjörn Larsson April 20, 2013 at 6:07 PM

Absolutely, I think Curiosity’s finds on Mars’ habitability tells us it is a race.

On the ice moons, I have seen a suggestion of using a “tidal habitable zone” (THZ) around gas giants as opposed to the “surface habitable zone” (SHZ) already established. If not most terrestrials will turn up as these water planets, the THZ can harbor more biomass (more and larger oceans) than the SHZ.

Don April 18, 2013 at 7:56 PM

Wouldn’t it be something, if somewhere out there, an intelligent alien life form had also been searching the galaxy for signs of life? And wouldn’t it be funny, if in the course of their search, they had studied our solar system and discarded our planet as a possible candidate, because it wasn’t located in their definition of a ‘habitable zone’?

Torbjörn Larsson April 18, 2013 at 10:01 PM

Note that the HZ is a work in progress, and has been redefined two times. (Kepler first used the radiative HZ without atmosphere models for the first rough analysis. And now when it uses the atmospheric HZ, with the exclusion of mini-Neptunes to boot, it was reworked by Kasting due to our greater understanding of greenhouse atmospheres due to AGW.)

It will be finessed even more, and we will also start to measure atmospheres, biosignatures and what not.

Kevin Stern April 19, 2013 at 1:43 AM

Or you know, they viewed us from afar and took off screaming. Declaring us unintelligent and hostile.

lcrowell April 19, 2013 at 3:25 PM

If on the plane of simultaneity (now) they are observing Earth they are witnessing Earth around time of Charlemagne. Without some sort of hyper-magnification technology far beyond our optics they would most likely not detect us humans. If they detected a 20% O_2 atmosphere with traces of methane and better yet signatures of photosynthetic life they would conclude this is a bio-planet.

LC

ITSRUF April 20, 2013 at 1:46 AM

It would be even more ironic if they discarded Earth as habitable because it is covered with water (which is incompatible with their sodium-based bodies).

Thomas guide April 18, 2013 at 8:36 PM

All they have is a rough estimate of the size and the orbit. Everything else is pure speculation. According to NASA Venus and Mars are in the habitable zone of our sun. Look at how well those 2 worlds worked out. Nasa leave the waterworld nonsense to Hollywood and concentrate on the facts.

Torbjörn Larsson April 18, 2013 at 9:56 PM

It is certainly not speculation, as you can see from the 2nd figure of “the Main Sequence” of planets after differentiation. As I noted above, we now know Mars was once habitable so confirm the habitable zone model. In fact, the model was built on knowledge of Mars climate.

The same goes for Venus. The model, which isn’t Nasa’s but a result of decades of efforts by Kasting, specifically incorporates Venus as a test case for the inner edge as you can see from the 3d figure: empirical HZ vs narrow HZ.

“As pointed out by Kasting et al. (1993), a third estimate for the IHZ boundary can be obtained from radar observations of Venus by Magellan spacecraft, which suggest that liquid water has been absent from the surface of Venus for at least 1 Gyr (Solomon & Head 1991). The Sun at that time was ~ 92% of the present day luminosity, according to standard stellar evolutionary models (Baraffe et al. 1998; Bahcall et al. 2001, See Table 2). The current solar ?ux at Venus distance is 1.92 times that of Earth. Therefore, the solar ?ux received by Venus at that time was 0.92 × 1.92 = 1.76 times that of Earth. This empirical estimate of the IHZ edge corresponds to an orbital distance of d = (1/1.76)^0.5 = 0.75 AU for the present day. Note that this distance is greater than Venus’ orbital distance of 0.72 AU because the constraint of surface water was imposed at an earlier time in the planet’s history.”

[ http://phl.upr.edu/press-releases/anewhabitablezone ; http://arxiv.org/abs/1301.6674 ]

Maybe you should concentrate on the facts before you denounce Nasa as a Hollywood subsidiary.

Thomas guide April 18, 2013 at 11:12 PM

Lots of technical jargon to backup your theory but the reality is they don’t know for sure if Mars was ever habitable, that is speculation. You don’t know if Venus ever had water, again that is speculation. You talk as though you were there a billion years ago. There is only one planet in the habitable zone and you’re on it. One is obviously too hot and the other is too cold. If they are in the right zone then they should be habitable today, but they are not, why? I’ll tell you why, because one is too close and the other is too far. That makes them out of the habitable zone as far as I’m concerned, As for this new discovery how do they know it’s a water world? Where is the evidence? It’s just wishful thinkng on Nasa’s part. Again show me the links that prove this world has water, I mena real evidence not just an artist’s picture and a NASA press release. All they have is a transit and a rudimentary measurement of the planet’s size and orbit. Those are the facts, everything else is made up.

I3VI5 April 19, 2013 at 3:36 AM

Do you know that you make absolutely no sense?

On one hand the “technical jargon” that Larsson used does not convince you because you don’t understand them. On the other hand you need proof of how NASA comes to this conclusions?! lol

Those at NASA have made an educated guess regarding these new announcements. Just because you are not smart enough to understand how they arrived at those conclusions, doesn’t mean they are wrong. So you can either accept those conclusions, or go study physics and then contradict them with arguments.

Lorin Ionita April 19, 2013 at 8:04 AM

“Those at NASA have made an educated guess regarding these new announcements.” Yes, but educated guesses do not make facts. Those are still speculations.

What I did not get is the “endless oceans” thing. How did they rule out even small patches of land?

Thomas guide April 19, 2013 at 2:33 PM

Read my post below, like I said its all guesses. They have no conclusive evidence that these planets have water. They have no conclusive evidence of temperature. They have no conclusive evidence of an atmosphere. Read the damned article, water worlds and Hawaiian balmy temperatures are just wishful thinking. If an astronomer living 1200 light years from here discovered Venus and Earth they might assume both worlds are balmy but they would be dead wrong wouldn’t they. There’s a big difference between educated guess and dreaming. Everyone seems to be dreaming and ignoring the facts. Fact is we don’t know a damned thing about these planets other than size and orbit. That’s it people, those are the facts. I can’t believe how eager people to just believe in nonsense.

William Sparrow April 19, 2013 at 10:00 PM

I won’t call into question your intelligence, as I3VI5 did an adequate job of that. I will, however, point out a couple of planetary facts that most of us learned in elementary school. The reason Venus is uninhabitable today is due to the runaway greenhouse effect caused by its CO2 heavy atmosphere and crushing atmospheric pressure. The reason Mars in uninhabitable today is due to a virtual lack of an atmosphere. Perhaps you’d do well to do a bit of research before criticizing established Planetary scientists and astronomers who dedicate their lives and careers to these fields. Otherwise, you just come off as an ignorant troll.

Thomas guide April 19, 2013 at 11:17 PM

I know it’s hard but try and think a little before you type. Why does Venus have a runaway greenhouse effect? It’s because it’s too close to the sun! That’s why it has no oceans and no ability to sequester any of the CO2 mister planetary genius. Why is this so hard to comprehend. We don’t have 3 planets with life for a reason, if you moved Earth a few million miles closer or farther than our present location it would spell doom for this planet. I will refrain from naming calling. Your posts seems to do a very good job of indicating your intelligence level.

Torbjörn Larsson April 20, 2013 at 5:26 PM

In short: The “jargon” is the references, I have added none. And it is not “my” theory (I wish it was! =D), I’m describing the work presented in the article and its context.

As for the rest, you are Gish galloping. There is no sense in describing what water is, and how we know its existance in the planetary system et cetera, when you obviously are not interesting in what we know and how we know it but is only senselessly trolling.

Ask a relevant question and I may answer. I don’t answer to trolling.

Torbjörn Larsson April 18, 2013 at 9:39 PM

I might as well repeat and fill in a commentary I left on the UT post on Kepler-62:

The nice thing with multiplanetary systems is that Kepler most often is capable to do two independent candidate detections (by transits and by transit differentials due to the planets affecting each other), making validated planets,

This is good, since they retired Tau Ceti f due to the redefinition of the habitable zone this will get us back up to ~ 50 % of stars with known habitables having 2 of them. Mars was surface habitable once, so should count as regards potential.

I suspect most systems will have 2 habitables, making us a bit underwhelming as regards terrestrial biospheres. Instead we may have more than the usual share of habitable ice moons, since Jupiter and Saturn are unusually large and so provides larger than the usual volume of gas giant tidal habitable zones.

Speaking of Mars, another Mars sized Kepler planet. IIRC there are 2 of them, certifying that Kepler can see them for sure.

Nitpick:

Kepler-22b, the smallest planet found in a habitable zone before the recent discoveries,

Only among the Kepler candidates shown in the figure. The Habitable Exoplanet Catalog shows 3 previous smaller planets. [ http://phl.upr.edu/projects/habitable-exoplanets-catalog ]

Thomas guide April 19, 2013 at 2:21 AM

These planets are unlike anything in our solar system. They have endless oceans,” said lead author Lisa Kaltenegger of the Max Planck Institute for Astronomy
Where exactly did she get that nonsense from?

From the full article:

The authors caution that “We do not know if Kepler-62e and -62f have a rocky composition, an atmosphere, or water.” Given its distance from the Sun, we’re not going to know any of those things about these planets any time soon. If we find enough systems that look like Kepler-62, it raises the odds that we’ll be able to find something that looks like it but is within the range of telescopes we can put into orbit.

The wild speculation ends.

Torbjörn Larsson April 20, 2013 at 5:15 PM

I’m not sure where you got your text, it is certainly not in article under the provided link, or what you are saying here, but it seems the wild speculation starts with you.

What we know is that, bar very exotic compositions, these planets will have between 15 and 75 % of water in their compositional makeup, see the 2nd figure above. Kaltenegger gets that from here extensive expertise in these matters.

“Endless oceans” seems an apt description.

Thomas guide April 21, 2013 at 6:07 AM

The text is from ars technica go check it out. Kaltenegger is dreaming about ocean worlds. She should refrain from guessing or using educated guesses until some facts can be obtained about these planets. The only known facts are size and orbit. Atmosphere is unknown, whether there is water there is unknown, temperature is unknown, magnetosphere is unknown. They don’t even know if these planets are rocky. Why is that so hard to comprehend. I don’t care what her expertise is. She doesn’t know for sure and that’s that.

Thomas guide April 21, 2013 at 4:00 PM

Also from wired science:

There is a great deal of uncertainty with the new worlds and scientists are careful about drawing any conclusions. The Kepler team members don’t know if the planets ”have a rocky composition, an atmosphere, or water,” they write in a paper available Apr. 18 in Science. Unless those properties can be found out, they “cannot determine whether [the exoplanets] are in fact habitable.”

Servé Vaessen April 19, 2013 at 5:50 AM

How do they know that Kepler 6-2e and 62-f are ocean worlds? The mass of the planets are unknown, so we can’t calculate their mean density and global composition. A cloudy sky for Kepler 62-e and warm and humid all the way to the poles? Distinctly different colours for Kepler 62-e and 62-f? This is stretching things way to far.The only thing we know about these planets are their diameter,orbital period and distance to their star.

lcrowell April 19, 2013 at 3:38 PM

As one scales up the mass of planets terrestrial planets leave off to neptunian planets. As a result super-Earth type of planets may have more liquids and gasses on them than Earth. It would not at all be surprising if many super-Earths are covered in oceans that are 10-100km deep or more with thick atmospheres.

LC

Torbjörn Larsson April 20, 2013 at 5:06 PM

The article seems to say it is less than a stretch than if you only have lower bounds of masses as per usual.

I suspect they know more about the inner 3 planets though, usually Kepler provides estimates of masses for compact multiplanetary systems from transition timing variations.

esmifra April 19, 2013 at 10:08 AM

Has JWST the capability to help us study this planets even further? If so, does anyone know or send me to a page that explaines how?

Kawarthajon April 19, 2013 at 12:33 PM
Torbjörn Larsson April 20, 2013 at 5:02 PM

If JWST isn’t up to the task, remember that

a) the nearby planet finding mission of TESS was just approved to be launched 2017, and will provide similar planets around 2020 _from the whole sky_ (due to ingenious design),

and

b) in the 20′s, many ground based 30+ m observatories will start to be used.

Andrew Thomas April 19, 2013 at 3:07 PM

Earth is habitable for us because we are perfectly adapted to the conditions through evolution and natural selection. Presumably any creatures which evolved on other planets with different conditions would also be perfectly adapted to those conditions. Aren’t we being a bit ‘species-centric’ talking about habitable zones at all, especially since we recently discovered life flourishing in places on Earth previously considered uninhabitable?

Torbjörn Larsson April 20, 2013 at 3:10 PM

We are using “selection bias” as a starting point for a perturbative analysis homing in on an unknown target, certainly.

As for the details of the history of a HZ vs extremophiles I would have to study up. But as far as I can see it is the knowledge of extremophiles and that they survive practically everywhere where we have liquid water that have firmed up the idea that looking for a planet in a HZ is a good starting point.

oliver penney April 20, 2013 at 7:44 AM

“These planets are unlike anything in our solar system. They have endless oceans”

so, like Europa then?

Torbjörn Larsson April 20, 2013 at 2:54 PM

Maybe, maybe not. The outer one can be ice covered, making it similar in that sense.

But a problem is that a deep ocean will most likely have (more or less exotic) water ice at the bottom of their deep oceans. That cuts off life promoting things like access to minerals and hydrothermal vents (sources for redox chemistry that produces organics and fuel metabolism).

On the other hand, a large terrestrial with water will surely have plate tectonics (large mass makes for more internal heat so more material churning, water makes the mantle material more pliable), which may break through the ice anyway. I don’t think I have seen anyone tackle this configuration yet.

Ana Castro April 21, 2013 at 7:43 PM

What’s up with all the ignorant criticism going on? I’m pretty sure there are complex mathematical models that explain in detail how researchers jumped to this conclusions, but since this article is aimed at a general public (read: we are not expected to have a doctoral degree in physics) it’s oversimplified.
Sure a lot of things in science are speculations, but extremely well based ones. The number of parameters scientists would need to consider for this to be “absolute” facts it’s ridiculous, but they know best how to pick the essential information. I mean, even arguments such as “because Venus is too near the sun, and mars is too far” hold a universe of detailed information within.
So seriously, the ones that are coming up with this, please stop.

Thomas guide April 19, 2013 at 2:58 PM

Thank you for having some common sense and calling them out on their bs.

Torbjörn Larsson April 20, 2013 at 5:31 PM

Since we have theories on geology, it is not “speculations” but likelihoods (educated guesses when hard to quantify).

I described the “endless oceans” here. With such deep oceans (and a massive planet) it is unlikely even hotspot volcanoes would reach the ocean surface, assuming they make it through the high pressure ices.

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