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December 16th, 2009


Of course, there are still 7 hours and 13 days left until the close of 2009, but I’ve got every confidence that the discovery of the decade has landed on the ground. The Mearth project has found a transiting 6.55 Earth-mass planet in orbit around the nearby red dwarf star GJ 1214. The parent star is bright enough, and the planet-star area ratio is large enough so that direct atmospheric characterization will be possible not just with JWST, but with HST. Incredible. I’m inspired, invigorated, envious. This discovery is a game changer.

The GJ1214 discovery is all over the news today. The coverage is deservedly laudatory, but interestingly, the most dramatic aspect of the detection received rather short schrift. This is easily the most valuable planet yet found by any technique, and the discovery, start to finish, required an investment of ~500K (along with the equivalent of 1-2 nights of HARPS time to do the follow-up confirmation and to measure the planet’s mass). By contrast, well over a billion dollars has been spent on the search for planets.

I’m milking that contrast for drama, of course. It’s true that GJ1214b is low-hanging fruit. The team with the foresight to arrive on the scene first gets to pick it. And the last thing I’m suggesting is a cut in the resources devoted to exoplanet research — it’s my whole world, so to speak. I do think, though, that Mearth epitomizes the approach that will ultimately yield the planets that will give us the answers we want. You search for transits among the brightest stars at given spectral type, and you design your strategy from the outset to avoid the impedance mismatches that produce bottlenecks at the RV-confirmation stage.

There’s a factor-of-fourteen mass gap in our solar system between the terrestrial planets and the ice giants, and so with the discovery of Gl 1214b (and the bizzare CoRoT-7b) we’re getting the “last first look” at a fundamentally new type of planet. CoRoT-7b is clearly a dense iron-silicate dominated object, but it likely didn’t form that way. Gliese 1214b’s radius indicates that it probably contains a lot of water. I think this is going to turn out to be the rule as more transiting objects in the Earth-to-Neptune mass range are detected.

So what next? With a modest increase in capability, Mearth is capable of going after truly habitable planets orbiting the very nearest stars. I think it’s time to put some money down…

  1. December 17th, 2009 at 13:17 | #1

    Well this has fairly nasty implications for the habitability of super-Earths located in the typical habitable zone – if they form with or outgas significant hydrogen envelopes, the pressures at the surface could be too high. Would there even be a surface? As I understand it, the interior of Uranus and Neptune are fluid because of the hydrogen mixing in and preventing the solidification of the high pressure water which would otherwise form an ice layer.

  2. coolstar
    December 20th, 2009 at 19:37 | #2

    While the Mearth project has always had winner written all over it, I can’t get all that excited over this particular find. In fact, I don’t even think it’s the most astrophysically interesting find of the project to date (a new double lined, eclipsing binary at the bottom of the main sequence gets my current vote).

  3. December 22nd, 2009 at 08:54 | #3

    The eclipsing M dwarf binary is more exciting? We already knew of CM Draconis and CU Cancri as well-known examples of such systems (and at slightly higher masses, YY Geminorum). GJ 1214b on the other hand represents a first good probe of a previously unknown region of parameter space.

  4. December 22nd, 2009 at 08:55 | #4

    Well there already exist systems like CM Dra and CU Cnc as previously-known examples of such systems. Low density super-Earths, not so much.

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