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Kepler 22-b: Another step closer to finding Earth-like worlds

The views expressed are those of the author and are not necessarily those of Scientific American.

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Comparison of "habitable zone" of Kepler 22 system and our solar system (NASA/Kepler)

Today sees the announcement that one of the “candidate” planets listed from NASA’s Kepler mission back in February is now confirmed, and it’s a key one. At 2.4 times the diameter of the Earth the planet Kepler 22-b also orbits its parent star (which is a slightly less massive G-dwarf star than the Sun and 25% less luminous) in 290 Earth-days, which places it within the nominal “habitable zone“. This system is about 600 light years from us.

This confirmation is one of a host of new results, as well as many new candidates. Altogether Kepler now has a staggering list of 2,326 possible planet detections, 207 of which are close to Earth in size and 680 are “super Earth” sized (i.e. up to about 10 times as large).

Interestingly, Kepler 22-b showed up as a transit signature just 3 days into Kepler’s science observations back in 2009, but the protocol is to wait for 3 confirmed transit events before calling a detection a bona-fide confirmed planet.

So here it is, arguably a much better candidate than some others we’ve heard about over the past 36 months (including the seemingly ill-fated Gliese 581 g that was claimed to be an Earth-like world). But as always there are many ifs, buts, and maybes. The habitable zone is estimated (with variations in method) assuming that a planet has an Earth-like atmosphere, since the greenhouse effect is a vital ingredient in setting the surface temperature to between 0 and 100 Celsius (freezing and melting point of water). And of course, for there to be liquid water on the surface (an assumed critical factor for life as we know it – as a biochemical-solvent and essential part of geophysical and climate cycles) there has to be water. Neither of these two basic items are known to exist in this case, and so as glorious as Kepler 22-b is, it represents the tip of the iceberg (no watery pun) in terms of what’s coming next and what we need to do next – which is get our hands on spectroscopic measurements of Earth-sized and super-Earth sized worlds.

How are we going to do that? Well, first we really need the James Webb Space Telescope to launch, and then it would be really, really cool if we could have something like the New Worlds Mission launch along with it…


Caleb A. Scharf About the Author: Caleb Scharf is the director of Columbia University's multidisciplinary Astrobiology Center. He has worked in the fields of observational cosmology, X-ray astronomy, and more recently exoplanetary science. His books include Gravity's Engines (2012) and The Copernicus Complex (2014) (both from Scientific American / Farrar, Straus and Giroux.) Follow on Twitter @caleb_scharf.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. Rouge77 5:29 pm 12/5/2011

    I would still consider planets like Gliese 581 c and d better candidates until Kepler-22 b:s mass is known. It could still be a mini-Uranus.

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  2. 2. caleb_scharf 5:50 pm 12/5/2011

    Right, although those other planets may be pretty chunky (i.e. up to 10 Earth masses) – I think the notable thing about Kepler 22-b is that it seems to be very firmly in a conservatively calculated habitable zone, which is not true of many other planets thus far.

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  3. 3. lump1 6:44 pm 12/5/2011

    What I find suspicious about Gliese 581-g as a cradle of life is that it’s tidally locked. On its dark side N2 and O2 are quite possibly cold enough to form lakes. We can’t begin to imagine the climactic havoc on a planet like this. Has anyone tried to model it? On the other hand, Kepler 22-b might very well have actual days and nights. With that sort of mass, I picture it having an incredibly thick atmosphere, but that might not be bad for life.

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  4. 4. ChazInMT 6:45 pm 12/5/2011

    Something people always seem to fail to mention. Does it spin? If the planet is tidally locked to its star, than it is a rock, blistering hot on one side and near absolute zero on the other. The fact that Earth spins is a 1 in 1 billion chance that we were smacked by a Mars sized planet 4 billion years ago, I doubt we’re going to find a “Habitable” planet in the habitable zone any time soon, just too many things need to happen for it to be more than a 1 in 1 billion chance.

    Cute news story I suppose.

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  5. 5. caleb_scharf 7:00 pm 12/5/2011

    The issue of planet spin is a big one, but not a show stopper. While it’s true that planets in the habitable zone of low-mass (M-dwarf) stars may become tidally locked (day length=year length) due to their proximity to the star, climate models indicate that temperate climates can actually still exist – the so-called “Eyeball Earth” scenario for example (a zone on the sunny side that’s moderately habitable). As for planet spin, I think most of us would say that all planets are likely to be formed with *some* spin, we just don’t know how much. For me the biggest qn right now is just a) whether there is an atmosphere on any of these smaller worlds and b) whether there’s any water, since our current models of planet formation suggest that getting water onto a rocky planet can be a very hit or miss (no pun) thing, i.e. somewhat random.

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  6. 6. YazdgerdIV 11:02 pm 12/5/2011

    What wonderful news! Has anyone seen this planet in anything other than an “artist’s rendering”? I would be curious as to what kinds of clouds are present, and if there is anyway to tell if there is a heavy CO2 presence there. How about rings, moons, or any other unknown ejecta? Is that blue color we see in the rendering water, ice, or some kind of ammonia in the atmosphere?

    Huge news, otherwise, and a great article! I am just so curious to find out more, if we do..

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  7. 7. caleb_scharf 11:18 pm 12/5/2011

    Unfortunately these pictures are simply artistic renderings of what it “might look like” – they’re optimistic and really just guesses – I don’t think they even include a notion of chemistry. We have no images, no data at present on anything other than the diameter of this particular planet and its estimated orbital distance from its star. It exists merely as 3 tiny, tiny dips in the light from the star when the planet blocks it from our point of view. We don’t even know what mass it is!

    Nonetheless, it is an important milestone for the Kepler mission, and helps with our statistical estimates of the number of these kinds of worlds out there.

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  8. 8. bigbopper 12:53 pm 12/6/2011

    I find it amusing when people immediately start speculating whether there could be life on this or any other “earth-like” planet we find. It’s like the Viking missions to Mars: jump straight to tests for life, instead of establishing a broader knowledge of Mars first. In the case of earth-like planets, first we’ll build up an inventory based on size, distance from the star, etc. Then we’ll need additional observations from more sophisticated space-based platforms looking at the composition of their atmospheres, etc. Maybe a couple of hundred years from now we’ll start to be able to speculate on which of these might be a cradle of life.

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  9. 9. kwlandry 5:25 pm 12/6/2011

    I’d have to add, in my opinion and I believe in the majority, confirming habitable planets and extraterrestrial life is a more important single discovery then a broader knowledge even though a broader knowledge is crucial and highly important in its own right and long term. One practical point is the discovery would fire investment in many fields and accelerate broader knowledge like no other event in the history of science.
    With that in mind, what are the plans to put in place technology that can confirm habitable planets and perhaps even life on a global scale? Will the James Webb or New Worlds launches provide greater capability to find possibly habitable planets or will they allow a level that will provide confirmation?


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  10. 10. caleb_scharf 8:26 pm 12/6/2011

    There are lots of *plans* for looking for the signs of life and habitable worlds, but not much funding! For a long time NASA and ESA have had long-range plans for devices like the Terrestrial Planet Finder, and even more ambitious space-based instruments that would image (with a few pixels) Earth-sized planets around nearby stars. All are expensive though. JWST (without New Worlds) and the next-generation very large ground based telescopes (30 meter diameters) will offer the possibility of confirming that such planets have atmospheres and even providing rudimentary data on the composition and temperatures of those atmospheres (in a few lucky cases). Ironically the most efficient way to *find* planets in the first instance is with much smaller instruments or missions, such as the MEarth project or MIT’s TESS space mission, or ESA’s PLATO mission.

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  11. 11. Postman1 10:43 pm 12/6/2011

    ChazInMT – Half of the rocky planets in our system have spin, so possibly 50% 0f extrasolar planets also spin. Just extrapolating.
    Otherwise: If this planet has several moons, is their mass included in the estimated mass? Would the existence of moons mean the planet could be smaller than the estimate? Would the moons (or rings for that matter) affect the transit shadow, making it appear larger? If the planet is a ‘small Neptune’, could it have an Earth size moon?

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  12. 12. cubeboy 7:43 pm 12/8/2011

    And then there’s the little matter of gravity: if Kepler 22b has 2.4 times the diameter of the earth, its gravity would be many times that of earth (does gravity increase as the square — or cube — of the diameter?), so roughly 6 to 14 times greater, assuming comparable density. It would certainly flatten us if we were there, and any hypothetical inhabitants would be a pretty heavy bunch …

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  13. 13. Quinn the Eskimo 11:34 pm 12/8/2011

    All this discussion is good! But, what I want to know is this: Can we start selling land yet?

    Cha-ching! It could fund the Research Grants.

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