Habitable, Not Earth-like

by Paul Gilster on October 18, 2011

I’ve put off writing about Wesley Traub’s paper on the frequency of planets in the habitable zone because I knew Adam Crowl had reservations about Traub’s method. We talked about this at the 100 Year Starship Symposium, which led to Adam’s agreeing to writing this piece for Centauri Dreams. How you define a habitable zone is, of course, a critical matter, especially when you’re dealing with a topic as compelling as extrasolar planets that can support life. Adam places Traub’s work in the context of earlier attempts at defining the habitable zone and finds HZ estimates different from Traub’s, though one is surprisingly similar to a much earlier study.

by Adam Crowl

The recent paper by Wesley Traub [reference below] has estimated the frequency of terrestrial (“Earth-like”) planets in the Habitable Zone (HZ) of their stars based on statistical analysis of the recent Kepler data release, but the frequency computed, of ~34(+/-14)% around FGK stars, is dubious due to the assumption of wide HZ limits. Before I discuss the specifics, let’s look at the modern history of the “Habitable Zone”.

The modern discussion really began with Stephen Dole’s “Habitable Planets for Man”, a RAND commissioned study from the early 1960s, eventually updated in 1970, and popularized with Isaac Asimov. Dole based his HZ limits on the criterion that a significant fraction of a terrestrial planet would experience a “hospitable climate”. He didn’t examine the effect of atmosphere, and derived the HZ limits of 0.725 – 1.25 AU, from just outside the orbit of Venus and a bit closer to the Sun than Mars at its closest. Applying statistical analysis to various features of the known planets, then extrapolating to other stars, Dole found that potentially 645 million Earth-like planets might exist in the Galaxy.

In the mid 1970s Michael Hart developed the first evolutionary models of the atmosphere of an Earth-like planet, finding Earth to be poised on a virtual knife-edge, tipping towards a Runaway Greenhouse if closer than 0.95 AU and Runaway Glaciation if further out from the Sun than 1.01 AU. When this criterion was applied to other stars, the frequency of Earth-like planets was less than 1 in a quarter million stars, or less than 400,000 Earths in a Galaxy of 100 billion stars.

Hart’s limits seemed overly sensitive to climate perturbations, and further work on the evolution of Earth’s atmosphere in the 1980s led to the paper “Habitable Zones Around Main Sequence Stars”, (Kasting, Whitmire & Reynolds, 1993) , which redefined the debate. What James Kasting and colleagues discovered was a powerful feedback loop between the levels of carbon dioxide in the atmosphere, geological weathering and the heat input from the Sun.

This creates a self-regulated surface temperature which can keep water in its liquid range out to a significant distance from the Sun. The chief uncertainty came from the complication of dry-ice clouds. Past 1.37 AU clouds of dry-ice begin forming and by 1.67 AU the cloud cover becomes total, negating the effectiveness of the carbon dioxide greenhouse effect. Some preliminary work on water clouds also suggests the inner radius of the habitable zone, just 0.95 AU, might be extended to closer to Venus.

Traub’s paper has somewhat more generous HZ limits. Traub examined three cases, with the ranges from 0.72-2.0 AU in the best case, a nominal HZ of 0.8-1.8 AU, and a “conservative” 0.95-1.67 AU. Using the observed planetary radii distribution and the orbital radii, Traub was able to compute the frequency of terrestrial planets in these HZ as 34(+/-14)%, with the extremes providing the error bar limits.

Here’s where just what is computed and why is important. The ranges used by Traub for the HZ apply to specifically liquid water compatible planets with extensive greenhouse gas atmospheres. Such worlds, with up to several bars of carbon dioxide for atmosphere, are only distantly “Earth-like”, much like Mars or Venus can be called Earth-like. The Earth we know, with an oxygen rich, carbon dioxide poor, atmosphere is somewhat more sensitive to climatic instability. If more conservative HZ ranges are used a quite different result is obtained.

The HZ, inside of the CO2 cloud limit found by Kasting, et.al., is the more restrictive 0.95-1.37 AU. This gives a frequency of just 13.3%. If we use the Continuously Habitable Zone (0.95-1.15 AU), also from Kasting, et.al., then the frequency drops to a mere 6.3%. Using Hart’s even more restricted range drops the frequency to less than 2%. Another caveat is that the planet frequency estimated is limited to stars in the mass-range 1.13-1.01 solar masses and is yet to be extended into the wider population of stars which make up ~80% of the Galaxy.

The HZ limits derived by Kasting et.al. assumed ocean-dominated terrestrial planets. The broader range of land dominated “desert planets” (Abe et.al., 2011), with water bodies limited to circum-polar lakes/ice-caps, increases the HZ range to 0.75-1.3 AU, and a corresponding frequency of 17.3%. Incidentally this range is equivalent to that derived by Dole’s (1964) ground-breaking study.

So, in conclusion, the high frequency of “Earth-like” planets derived by Traub, is tempered somewhat when a more precise Earth-like Habitable Zone range is used. Planets warm enough for liquid water thanks to multi-bar atmospheres of carbon dioxide, methane or hydrogen, while probably conducive to extremophiles, aren’t “Earth-like” as usually understood, and this caveat should be more widely appreciated when making such estimates.

The paper is Traub, “Terrestrial, Habitable-Zone Exoplanet Frequency from Kepler,” available online as a preprint. Other references:

Y.Abe, A.Abe-Ouchi, N.H.Sleep, and K.J.Zahnle. “Habitable Zone Limits for Dry Planets”, Astrobiology, Volume 11, Issue 5, pp. 443-460 (2011).

S.H. Dole, Habitable Planets for Man, Blaisdell, New York (1964).

M.H. Hart, “Habitable zones about main sequence stars”, Icarus, 37: 351-357 (1978).

J.F. Kasting, D.P. Whitmire and R.T. Reynolds. “Habitable Zones Around Main Sequence Stars” Icarus 101: 108-128 (1993).

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Eniac October 22, 2011 at 22:37

Does it matter how soon exactly ? Anyhow it started, and for most of the time earth that earth has been in the “habitable” category , it has been populated by one celled organisms only , and therefor using simle logic this is a reasonable expectation to have from any other REALLY similar planet, because earth is the only solid evidence we have sofar.

Yes, it does matter. For the argument to have any value, life really needed to have started “right away”. One billion years of lifelessness gives much more credence to the hypothesis that abiogenesis is hard.

Your “simple logic” is faulty because our sample of one (Earth) is strongly biased towards those planets that do have life. This is because planets without life would have been unavailable as a sample, as they do not have scientists or statisticians on them. Such a strongly biased sample makes conclusions about frequency impossible.

Ole Burde October 23, 2011 at 12:56

Eniac
” …planets without life would have been unavaiable as a samble..” , true enough , but so would planets WITH life ,exept for earth .
There are always two comlementarey ways of dealig with the unknown . One is to establish a theoretical framework of theories, and gradualy verify their power of prediction . Another more imediate way is to use only known facts and to conclude from them only a temporary “workmans hypotesis” .
Hopefully we will soon have more facts to work with .
If it should be true that no signs of life can be found in the 100 LY nabourhood , what should we plan for then ?
How can a one-way colonyship survive when it reaches a dead world ?
In such a scenario the whole idea of interstellar starship becommes much , much more difficult , and therefore could get postponed into the far future, a future where earth might be running out of raw materials , and maybe entering a period of increasing wars and general decline of civilisation .

andy October 23, 2011 at 15:28

Have to question whether given the uncertainty in the conditions necessary for abiogenesis and the uncertainty we have as to when the first organisms emerged on this planet, we can really state with any degree of confidence what the wait time between the occurrence of suitable conditions and the origin of life actually was.

Ole Burde October 23, 2011 at 18:03

True enough , no certainty about the time it takes for life to start or what the necesary conditions are . At this time there are no certainties about almost anything , but if we DO want a set of asumtions to work with , it seems to ME that we have to use the only wellknonwn habitable planet as a statistical model for these asumtions . The most important one is that earth has only been sending out radiosignals for a very small fracion of its life-history , so IF we encounter any planet with signs od life ,the overwhelmimg chance is that there will be no toolmaking annimals hiding there .
And THAT would make it the kind of tagetstar , to which it would be possible to travel MUCH sooner than a completely different scenario , where a starship arives at a dead world and have to becapable of building closed selfsurplying habitats from scratch ,where several thousand people can live and thrive until perhabs thousand of years later the planet can be “terraformed” .

Rob Henry October 23, 2011 at 20:13

To elaborate on Andy’s line of thinking, I note that nearly all abiogenesis scenarios envisage far from equilibrium conditions. If such conditions occur over a large area (such as an ocean full of pre-biotic soup), then they will rapidly “wind down”, and, no matter how low the chance of abiogenesis, must thus occur very soon after suitable conditions first arise.

Worse still, if we take unconventional view that the first UNAMBIGOUS evidence for life was close to its actual start, then Andy’s wait time is comparable to many estimates of the time still left where our biosphere can still regulate its temperature. In that case, even if the problem of the first paragraph did not apply, then when we adjust for the observer effect, we can no longer claim that the fossil record implies this period for a typical life bearing planet is less than ANY finite period.

Rob Henry October 23, 2011 at 20:17

To elaborate on Andy’s line of thinking, I note that nearly all abiogenesis scenarios envisage far from equilibrium conditions. If such conditions occur over a large area (such as an ocean full of pre-biotic soup), then they will rapidly “wind down”, and, no matter how low the chance of abiogenesis, life must thus occur very soon after suitable conditions first arise.

Worse still, if we take the unconventional view that the first UNAMBIGOUS evidence for life was close to its actual start, then Andy’s wait time is comparable to many estimates of the time still left where our biosphere can still regulate its temperature. In that case, even if the problem of the first paragraph did not apply, then when we adjust for the observer effect, we can no longer claim that the fossil record implies this typical period for a life bearing planet is less than ANY finite period.

Eniac October 24, 2011 at 9:51

If it should be true that no signs of life can be found in the 100 LY nabourhood , what should we plan for then ?
How can a one-way colonyship survive when it reaches a dead world ?

We should plan for staying in space, exploring the dead planets, and perhaps for seeding some with life, where appropriate. Any colony ship will have to be self-sufficient, anyway. A fresh supply of light, asteroids, and icy bodies will enable it not only to survive, but to thrive and grow. It will most likely come from a place where people have learnt how to live in space long before they set out for the stars. It may not even have people on board.

Eniac October 24, 2011 at 9:59

Andy:

Have to question whether given the uncertainty in the conditions necessary for abiogenesis and the uncertainty we have as to when the first organisms emerged on this planet, we can really state with any degree of confidence what the wait time between the occurrence of suitable conditions and the origin of life actually was.

Right. I like to say it is 1 Gy +/- 1 Gy, and I think it puts a big huge dent in the whole “soon after” argument. Where does that one come from, anyway? Must have been in one of those popular books I have not read, like all these Rare Earth arguments that keep crawling out from under the rocks.

Ole Burde October 24, 2011 at 14:43

Eniac
” We should plan to stay in space …..”
It might be a good plan if “we” ever get to live , work and reproduce in great numbers in space , in away that is completely independent of earth .
If this ” Gerald O’Neil” type of future should be the way things develop , then we are in no hurry to go anywhere ,and any sensible person would want to wait until all problems concerning starflight has been solved in the best possible way .
On the other hand , there might another equaly posible future , where earth starts running out of raw materials long before any serious industrial activities has been etablished in space . In this scenario the only chance of getting anywhere is to find a shortcut using not-so-nice methods including gambling the future the crew on the chance they won’t be poisoned by alien ecology , and including minimizing the size of ship and crew using every trick in the book.
Which kind of future seems more likely ?

andy October 24, 2011 at 14:58

Right. I like to say it is 1 Gy +/- 1 Gy, and I think it puts a big huge dent in the whole “soon after” argument.

Precisely. People see what they want to see rather than what is there, because what is there is so uncertain.

Holger October 24, 2011 at 16:05

@Eniac: How did you arrive at an upper limit of 2 Gy? There is “reliable fossil evidence of the first life found in rocks 3.4 Gyr old”, according to Wikipedia (http://en.wikipedia.org/wiki/Abiogenesis , quoting http://www.lifescientist.com.au/article/398092/world_oldest_fossils_reveal_earliest_life_earth/ ), so abiogenesis cannot have taken more than (4.5 Gy minus 3.4 Gyr=) 1.1 billion years, even if Earth was “habitable” from day 1.

Ronald October 25, 2011 at 6:48

Regardless of how long it took exactly for life to arise (abiogenesis), there seem to have been certain barriers or thresholds that had to be surpassed before earth became even potentially suitable for life. I am particularly thinking of:
- formation of the crust, the oceans and other surface water (took about 0.2 gy).
- the Late Heavy Bombardment (until about 3.8 gy ago, that is 0.7 gy after origin).
- the very high UV levels of the young sun (tens to a few hundred times present level) that had to subdue to a survivable level (several hundred million years?).

And particularly for aerobic, Eukaryote life:
- saturation of the O2 sinks of the earth, building up of atmospheric O2 levels (>= 1gy?), ozone layer.
Maybe also, with regard to the above discussion on atmospheres:
- reduction of the primordial CO2 atmosphere, building up of C stores in the earth crust (x gy?).

I do not exactly know the precise time limits for each of the above factors and there may be more unknown ones.
But if conditions on earth were very unfavorable to the rising and surviving of life until about 0.7 or 0.8 gy and life originated at about 1 or 1.1 gy, that means that first (surviving) life arose ‘only’ about 0.2 – 0.4 gy after conditions became suitable.
In fact, there are also indications that life arose much earlier, about 3.8 gy ago, see for example:
http://www.eurekalert.org/pub_releases/2006-07/uoc–uss072006.php
In which case life arose at only 0.7 gy or less.

It is conceivable and in a way even an elegant thought that there is a clockwork mechanism for a solar type star/terrestrial planet combination to become ‘ready for life’.

Eniac October 25, 2011 at 9:52

How did you arrive at an upper limit of 2 Gy? There is “reliable fossil evidence of the first life found in rocks 3.4 Gyr old”

I think that characterization of the evidence as “reliable” is very generous. I followed it once, and was not impressed. Fossil evidence for microbes is plagued by hopeful interpretations and a tendency to discount non-biological explanations. Remember the fossil “bacteria” in Mars meteorites?

So, yes, with my +/- 1 Gy I include the possibility that some of the earliest findings are not conclusive.

Ole Burde October 25, 2011 at 14:43

Lets be honest about it . We all have our own psycological reasons to prefare a certain general variation of how the future should reveal itself . My own personal “favorite future” is one where it turns out that onecelled life is abundant in the universe , and where earth is the only place inside thousands of LY with a toolmaking lifeform , ME ! . This is , I believe , my favorite because it will create many powerfull reasons for humans to get their act together as quickly as possible. On the other hand it might be my favorite because i am a gready imperialisic pig , spoiling for an opportuninity to steel planets belonging to tall blue really cool natives !
So far most new evidence surprisingly points in this rather wishfull-thinking direction as far as the universe is concerned . In a few years this dream might be scientific truth .
The opposite asumtion , that the universe is an almost lifeless place , also has its believers , who argues for it with equal passion and stubbornness . I have never been capable of understanding their choice of favorite future .
Anyhow we will know in hopefully no more than 25 years .

Eniac October 25, 2011 at 20:06

I’d put it somewhat differently: Some of us have a favorite future and search for arguments in its favor, others just want to follow the evidence as to what that future is, without playing favorites.

Ole Burde October 26, 2011 at 2:45

” ….others just want to follow the evidence…”
Hmmm…. Like deciding deciding against the POTENTIAL existence of extraterestrial MICROBES based exclusively on all the things we dont know yet ,like the lack of radiocomunication ? hmmm… ?

Adam Crowl October 26, 2011 at 3:08

Eniac, the latest figure for earliest *definite* Life is from microfossils discovered by Martin Brasier, chief skeptic of all previous claims to very ancient fossils. If he thinks they’re real, then you can trust the claim. About 3.43 Gya is the current date from work published this year.

Ronald October 26, 2011 at 7:44

Eniac: “Some of us have a favorite future and search for arguments in its favor, others just want to follow the evidence as to what that future is, without playing favorites.”

How true, the comment of the day!

The tendency to selectively and exclusively search for and accept arguments that support and confirm one’s own worldview is typical of religions.

To allow one’s views to be continuously adjusted by verifiable evidence, even if the result is not according to one’s liking, is a scientific worldview.

Eniac October 26, 2011 at 10:43

Ole: Nobody decided anything, I hope, and of course ET life POTENTIALLY exists. We are debating if they do exist, actually. Just because the evidence is scanty does not mean we have to give in to wishful thinking.

Adam: Thanks for the tip, I will take another look. However, if I change my mind it will not be because Brasier turned from skeptic to believer, but because he went the extra mile to try to think of and exclude (or not) alternative origins for the “fossils”. And of course, presents rock-solid data on their dating.

andy October 26, 2011 at 13:41

The tendency to selectively and exclusively search for and accept arguments that support and confirm one’s own worldview is typical of religions.

The real trick is realising bias in oneself, and that is probably impossible. It is certainly possible to convince oneself that you are unbiased but that does not make it so! There is a reason why scientific results need to be scrutinised by various third parties in a peer review process before they are published.

You certainly appear to be biased towards the pessimistic scenarios. Just because the evidence is scanty does not mean we should draw the unfavourable conclusions either…

andy October 26, 2011 at 13:44

(Whoops above comment was originally addressed to Eniac before redrafting to quote Ronald’s post… was pointing out the Eniac appears to have a strong bias towards the pessimistic scenarios)

Ole Burde October 26, 2011 at 17:52

This is a happy ending , or maybee beginning ! if ET life potentially exists , especially microbes , then we can relate to and debate the internal logic in a SCENARIO including their existence without necesaryly deserving to be blamed for “… to selektively and exclusively search for arguments that support and confirm …”
The definition of a scenario includes the possiblity of becomming true.
The use of a certain scenario is to set up a kind of playground to be expored in paralell with others . While arguing inside the scenario ,the internal logic of it might seem ” selective” ,when seen from an observer who does not agree to come inside and play !
Children learns extremly fast playing games , and so do mathematicians . They define a new world-game of rules and start playing around , sometimes it can lead them to very real and very powerful conclutions .
The same might be true of a scenario incuding only ET microbes .

Eniac October 26, 2011 at 19:45

Andy, Ole, If you look back at other threads, you will find that I have often argued against Rare Earth arguments and explored the possibilities for life in the solar system, as we know it and perhaps not. I have also at times vehemently rejected arguments for “no life” which I perceived as inconclusive.

I believe it is not only ok, but productive to take a position when arguing about the evidence. As long as you are willing to move from this position if you are no longer able to support it with rational arguments. It is good to even change your position once in a while without being forced by the evidence, to better explore the alternatives.

That said, Andy is of course right that it is very difficult to be truly unbiased, all I am saying is we have to try. It should not be too hard in this forum, where most of us do not hold much of a stake in the answer. The problem is much bigger when reputations, politics, or commercial interests are involved.

Ronald October 27, 2011 at 6:15

It’s ok andy. I usually call myself a realist, with a strong touch of optimism.

Ref. to what I stated in my comment above: it seems that first (surviving, our ancestral) life on earth appeared already at age 1 – 1.1 gy at the latest (i.e. this is what we have definite evidence for). That is only 0.2 – 0.4 gy after the earth became suitable for life. Again, maybe earlier.
First Eukaryotes and complex (multi-celled) life much later, which again may have to do with the earth being suitable for it: O2 sinks and atmospheric build-up and so.
This is what makes me a bit optimistic: it looks as if various types of life indeed appeared rather quickly after the earth as a planet was ‘ready’ for it, meaning passing certain thesholds.
Future spectroscopic analysis missions may be able to establish this for solar type stars with terrestrial planet combinations of various ages.

Eniac October 27, 2011 at 9:41

I actually consider the “no-life” position optimistic: It excludes hostile aliens and a galaxy already fully occupied. It also does not implicate a bleak future for star travel to explain the absence of star travelers.

It would be a job-killer for astrobiologists, though, which is probably why those tend to argue for life :-)

Ron S October 27, 2011 at 10:35

In my view both the “no life” and fecund positions are positive, just that each offers different benefits and opportunities and, yes, risks. What’s important is that we not place our bets (or project our beliefs) on one side or the other in the absence of evidence. Besides, we may never know the truth; you cannot be certain that if you persist at looking more closely or farther away that life and ETI might finally show up somewhere. If we stop searching (a not unjustifiable choice) that only places the onus on others, should they choose and if they exist, to find us.

Ronald October 27, 2011 at 11:26

Astronomers have just discovered 3 giant (Jupiter to super-Jupiter) planets orbiting aging (off the main sequence) KIII giant stars at distances of 1 – 2 AU. Which makes one think of either the possibility of (former) life and habitable moons?

http://www.physorg.com/news/2011-10-planets-mystery-solar.html

They are also already in the Extrasolar Planets Encyclopedia (exoplanet.eu)

Eniac October 27, 2011 at 19:50

Ron: I think you nailed it exactly. Only, hopefully there will be a time when we or our probes spread out to the stars and examine hundreds, thousands, millions of systems up close. If by then we have not found signs of life, the odds will be heavily in favor of “no life”, to such a degree that “know” and “certain” would apply.

ljk September 12, 2012 at 9:04

11 September 2012

** Contact information appears below. **

Text & Images:

http://www.jpl.nasa.gov/news/news.php?release=2012-285

EXTREME LIFE FORMS MIGHT BE ABLE TO SURVIVE ON ECCENTRIC EXOPLANETS

Astronomers have discovered a veritable rogues’ gallery of odd exoplanets — from scorching hot worlds with molten surfaces to frigid ice balls.

And while the hunt continues for the elusive “blue dot” — a planet with roughly the same characteristics as Earth — new research reveals that life might actually be able to survive on some of the many exoplanetary oddballs that exist.

“When we’re talking about a habitable planet, we’re talking about a world where liquid water can exist,” said Stephen Kane, a scientist with the NASA Exoplanet Science Institute at the California Institute of Technology in Pasadena. “A planet needs to be the right distance from its star — not too hot and not too cold.” Determined by the size and heat of the star, this temperature range is commonly referred to as the “habitable zone” around a star.

Kane and fellow Exoplanet Science Institute scientist Dawn Gelino have created a resource called the “Habitable Zone Gallery.” It calculates the size and distance of the habitable zone for each exoplanetary system that has been discovered and shows which exoplanets orbit in this so-called “goldilocks” zone.

The Habitable Zone Gallery can be found at http://www.hzgallery.org

The study describing the research appears in the Astrobiology journal and is available at http://arxiv.org/abs/1205.2429

But not all exoplanets have Earth-like orbits that remain at a fairly constant distance from their stars. One of the unexpected revelations of planet hunting has been that many planets travel in very oblong, eccentric orbits that vary greatly in distance from their stars.

“Planets like these may spend some, but not all of their time in the habitable zone,” Kane said. “You might have a world that heats up for brief periods in between long, cold winters, or you might have brief spikes of very hot conditions.”

Though planets like these would be very different from Earth, this might not preclude them from being able to support alien life. “Scientists have found microscopic life forms on Earth that can survive all kinds of extreme conditions,” Kane said. “Some organisms can basically drop their metabolism to zero to survive very long-lasting, cold conditions. We know that others can withstand very extreme heat conditions if they have a protective layer of rock or water. There have even been studies performed on Earth-based spores, bacteria and lichens, which show they can survive in both harsh environments on Earth and the extreme conditions of space.”

Kane and Gelino’s research suggests that habitable zone around stars might be larger than once thought, and that planets that might be hostile to human life might be the perfect place for extremophiles, like lichens and bacteria, to survive. “Life evolved on Earth at a very early stage in the planet’s development, under conditions much harsher than they are today,” Kane said.

Kane explained that many life-harboring worlds might not be planets at all, but rather moons of larger, gas-giant planets like Jupiter in our own solar system. “There are lots of giant planets out there, and all of them may have moons, if they are like the giant planets in the solar system,” Kane says. “A moon of a planet that is in or spends time in a habitable zone can be habitable itself.”

As an example, Kane mentioned Titan, the largest moon of Saturn, which, despite its thick atmosphere, is far too distant from the Sun and too cold for life as we know it to exist on its surface. “If you moved Titan closer in to the Sun, it would have lots of water vapor and very favorable conditions for life.”

Kane is quick to point out that there are limits to what scientists can presently determine about habitability on already-discovered exoplanets. “It’s difficult to really know about a planet when you don’t have any knowledge about its atmosphere,” he said. For example, both Earth and Venus experience an atmospheric “greenhouse effect” — but the runaway effect on Venus makes it the hottest place in the solar system. “Without analogues in our own solar system, it’s difficult to know precisely what a habitable moon or eccentric planet orbit would look like.”

Still, the research suggests that habitability might exist in many forms in the galaxy — not just on planets that look like our own. Kane and Gelino are hard at work determining which already-discovered exoplanets might be candidates for extremophile life or habitable moons. “There are lots of eccentric and gas giant planet discoveries,” Kane says. “We may find some surprises out there as we start to determine exactly what we consider habitable.”

Contact:
Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.
+1 (818) 354-4673
whitney.clavin@jpl.nasa.gov

NASA’s Exoplanet Science Institute at Caltech manages time allocation on the Keck Telescope for NASA. NASA’s Jet Propulsion Laboratory in Pasadena, Calif., manages NASA’s Exoplanet Exploration program office. Caltech manages JPL for NASA.

More information about exoplanets and NASA’s planet-finding program is at http://planetquest.jpl.nasa.gov

[ Written by Josh Rodriquez ]

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