Authors: E. Miller-Ricci, J. J. Fortney

(Submitted on 6 Jan 2010)

Abstract: The newly discovered planet GJ 1214b is the first known transiting super-Earth requiring a significant atmosphere to explain its observed mass and radius. Models for the structure of this planet predict that it likely possesses a H-He envelope of at least 0.05% of the total mass of the planet.
However, models without a significant H-He atmosphere are not entirely ruled out by the available data.

Here we explore a range of possible atmospheres for the planet, ranging from solar composition gas, to pure CO_2 or water (steam). We present transmission and emission spectra for each of these cases.

We find that, if GJ 1214b possesses a hydrogen-rich atmosphere as expected, then the primary transit depth for such an atmosphere would vary at a level of up to 0.3% as a function of wavelength, relative to the background light of its M-dwarf host star. Observations at this level of precision are potentially obtainable with current space-based instrumentation. Successful detection of the transmission signature of this planet at the ~0.1% level would therefore provide confirmation of the hydrogen-rich nature of the planetary atmosphere.

It follows that transmission spectroscopy at this level of precision could provide a first glimpse into answering the question of whether planets in the super-Earth mass regime (1 – 10 M_Earth) more closely resemble large terrestrial planets or small gas giant planets.

Comments: submitted to ApJ Letters

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Cite as: arXiv:1001.0976v1 [astro-ph.EP]

Submission history

From: Eliza Miller-Ricci [view email]

[v1] Wed, 6 Jan 2010 21:07:12 GMT (141kb)

http://arxiv.org/abs/1001.0976

Chris, that ocean planet sounds interesting, but the depth of the ices can be deeper or even absent given the right thermal profile and the presence of dissolved minerals, which depress the melting points of all the high-pressure phases that can be studied – Ice VI & VII, for example. There’s no reason why some kind of high pressure/temperature cryovolcanism can’t occur either, ferrying minerals up from the silicates below, given a decent heat supply.

Well, it’s nice to see Astronomy unfurling as we enter a new decade. Especially of this sort-Super-Earth Habitability will surely attract attention in Media =]

Good luck for anything, Alex

As on Earth, carbon dioxide would likely be the limiting feedstock and would be completely sequestered away into biomass. An absence of CO2 in an atmosphere could then mean 2 things: 1) There is no carbon and thus no carbon-based life, 2) there is carbon-based life which has sequestered all the CO2. Turning this around, the presence of CO2 would be a strong indicator of the absence of carbon-based life, as on Mars and Venus.

Super-Earths of a certain size (anyone know that size?) will retain hydrogen due to their deeper gravity well and thus should pretty much always have the reducing conditions which would prohibit oxygen from forming and animals from evolving. This ought to be a strict limit on the size of any inhabited (or inhabitable) planets we might find. Is this true? Has it been recognized?

Get rid of the thick atmosphere, possibly by sequestering it in the coean, and shade the planet to lower the temperature. Then build a floating, semi ‘Supra-mundane’ planet on the surface of the ocean. Just some floating Islands to start with, getting larger and larger until most of the surface is covered. Hopefully there will be resources dissolved in the ocean that we can extract.

One more thing – if the atmosphere is Hydrogen, surely it will have a higher scale hieight anyway to get the same surface pressure?