The atmosphere of GJ 1214 b

Recent Transits of the Super-Earth Exoplanet GJ 1214b

Slightly smaller radius estimate than the discovery paper, but agrees within the error bars.

(I didn't see a thread already made but I thought we had one... )

UniverseToday and others are reporting that Gliese 1214 b has been found to have a water vapour -rich atmosphere and/or a thick haze layer.

ESO announcement:
http://www.eso.org/public/news/eso1047/

Observational evidence for a metal rich atmosphere on the super-Earth GJ1214b
http://arxiv.org/abs/1103.2370

Quote :

We report observations of two consecutive transits of the warm super-Earth exoplanet GJ1214b at 3.6 and 4.5 microns with the Infrared Array Camera instrument on-board the Spitzer Space Telescope. The two transit light curves allow for the determination of the transit parameters for this system. We find these paremeters to be consistent with the previously determined values and no evidence for transit timing variations. The main investigation consists of measuring the transit depths in each bandpass to constrain the planet's transmission spectrum. Fixing the system scale and impact parameters, we measure R_p/R_star=0.1176 (+0.0008/-0.0009) and 0.1163 (+0.0010/-0.0008) at 3.6 and 4.5 microns, respectively. Combining these data with the previously reported MEarth Observatory measurements in the red optical yields constraints on the GJ1214b's transmission spectrum and allows us to rule-out a cloud-free, solar composition (i.e., hydrogen-dominated) atmosphere at 4.5 sigma confidence. This independently confirms a recent finding that was based on a measurement of the planet's transmission spectrum using the VLT. The Spitzer, MEarth, and VLT observations together yield a remarkably flat transmission spectrum over the large wavelength domain spanned by the data. Consequently, cloud-free atmospheric models require more than 30% metals (assumed to be in the form of H2O by volume to be consistent with all the observations.

After reading it, I was confused.

I'm assuming when they say metal-rich, they mean hydrogen-/heliuem-poor.
While anything from H2O is considered metal-rich.

If so, the paper only seems to say that the atmosphere is H/He poor.
And that it has a cloud/haze cover.

If this is incorrect, let me know.

That's how I understood it. They ruled out a hydrogen dominated atmosphere like you would expect if the planet got its atmosphere from accreting it directly from the disk. This 'metal' rich atmosphere suggests the planet has migrated inward from beyond the ice line.

There is probably still some hydrogen/helium in there though despite them not being the major constituent of the atmosphere. Water vapour is probably the dominant component.

Broadband Transmission Spectroscopy of the super-Earth GJ 1214b suggests a Low Mean Molecular Weight Atmosphere
http://arxiv.org/abs/1104.0011

Quote :

We used WIRCam on CFHT to observe four transits of the super-Earth GJ 1214b in the near-infrared. For each transit we observed in two bands nearly-simultaneously by rapidly switching the WIRCam filter wheel back and forth for the duration of the observations. By combining all our J-band (~1.25 microns) observations we find a transit depth in this band of 1.338\pm0.013% - a value consistent with the optical transit depth reported by Charbonneau and collaborators. However, our best-fit combined Ks-band (~2.15 microns) transit depth is deeper: 1.438\pm0.019%. Formally our Ks-band transits are deeper than the J-band transits observed simultaneously by a factor of 1.072\pm0.018 - a 4-sigma discrepancy. The most straightforward explanation for our deeper Ks-band depth is a spectral absorption feature from the limb of the atmosphere of the planet; for the spectral absorption feature to be this prominent the atmosphere of GJ 1214b must have a large scale height and a low mean molecular weight. That is, it would have to be hydrogen/helium dominated and this planet would be better described as a mini-Neptune. However, recently published observations from 0.78 - 1.0 microns, by Bean and collaborators, show a lack of spectral features and transit depths consistent with those obtained by Charbonneau and collaborators. The most likely atmospheric composition for GJ 1214b that arises from combining all these observations is less clear; if the atmosphere of GJ 1214b is hydrogen/helium dominated then it must have either a haze layer that is obscuring transit depth differences at shorter wavelengths, or significantly different spectral features than current models predict. Our observations disfavour a water-world composition, but such a composition will remain a possibility until observations reconfirm our deeper Ks-band transit depth or detect features at other wavelengths. [Abridged]

Seems this one was written at roughly the same time as the previous paper in this thread. They do acknowledge it in a footnote:

Quote :

While this paper was in the late stages of revision, Desert et al. (2011) presented Spitzer 3.6 and 4.5 µm channel observations of the transit of GJ 1214b. They find similar transit depths in these bands to those found by Bean et al. (2010) and Charbonneau et al. (2009) in the very near-infrared. If methane is present in the atmosphere of GJ 1214b it should cause increased absorption in the 3.6 µm channel; as this is not observed, if the atmosphere of GJ 1214b is hydrogen/helium dominated, the combination of all the observations to date argues in favour of the hazy hydrogen/helium dominated model without methane.

High Resolution, Differential, Near-infrared Transmission Spectroscopy of GJ 1214b
http://arxiv.org/abs/1104.1173

Quote :

The nearby star GJ 1214 hosts a planet intermediate in radius and mass between Earth and Neptune, resulting in some uncertainty as to its nature. We have observed this planet, GJ 1214b, during transit with the high-resolution, near-infrared NIRSPEC spectrograph on the Keck II telescope, in order to characterize the planet's atmosphere. By cross-correlating the spectral changes through transit with a suite of theoretical atmosphere models, we search for variations associated with absorption in the planet atmosphere. Our observations are sufficient to rule out tested model atmospheres with wavelength-dependent transit depth variations >5e-4 over the wavelength range 2.1 - 2.4 micron. Our sensitivity is limited by variable slit loss and telluric transmission effects.
We find no positive signatures but successfully rule out a number of plausible atmospheric models, including the default assumption of a gaseous, H-dominated atmosphere in chemical equilibrium. Such an atmosphere can be made consistent if the absorption due to methane is reduced. Clouds can also render such an atmosphere consistent with our observations, but only if they lie higher in the atmosphere than indicated by recent optical and infrared measurements.
When taken in concert with constraints from other groups, our results support a consensus model in which the atmosphere of GJ 1214b contains significant H and He, but where methane is depleted. If this depletion is the result of photochemical processes, it may also produce a haze that suppresses spectral features in the optical.

Some parallels to GJ 436b which has also been reported to be depleted in methane. More research into photochemistry on M-dwarf planets needed?

In the end, has GJ 1214 b hydrogen-helium atmosphere or not?

Edasich wrote:

In the end, has GJ 1214 b hydrogen-helium atmosphere or not?

Yeah, I'd love to fast-forward to the end to see how this plays out, too. So far though, looks like the most conclusive we have is:

The paper I just posted wrote:

When taken in concert with constraints from other groups, our results support a consensus model in which the atmosphere of GJ 1214b contains significant H and He, but where methane is depleted. If this depletion is the result of photochemical processes, it may also produce a haze that suppresses spectral features in the optical.

Sirius_Alpha wrote:

Edasich wrote:

In the end, has GJ 1214 b hydrogen-helium atmosphere or not?

Yeah, I'd love to fast-forward to the end to see how this plays out, too. So far though, looks like the most conclusive we have is:

The paper I just posted wrote:

When taken in concert with constraints from other groups, our results support a consensus model in which the atmosphere of GJ 1214b contains significant H and He, but where methane is depleted. If this depletion is the result of photochemical processes, it may also produce a haze that suppresses spectral features in the optical.

.

I see. Maybe carbon monoxide? But perhaps methane itself comes from its photo-dissociation, right?

Edasich wrote:

I see. Maybe carbon monoxide? But perhaps methane itself comes from its photo-dissociation, right?

So let's go see what the photo-chemistry model predicts...

The Atmospheric Chemistry of GJ 1214b: Photochemistry and Clouds

Various possibilities, but still no definite conclusions yet. Various possibilities include hydrocarbon hazes, clouds of zinc sulphide and/or potassium chloride, more efficient methane photolysis than predicted...

Optical to near-infrared transit observations of super-Earth GJ1214b: water-world or mini-Neptune?
http://arxiv.org/abs/1111.2628

Quote :

GJ1214b is thought to be either a mini-Neptune with a thick, hydrogen-rich atmosphere, or a planet with a composition dominated by water. In the case of a hydrogen-rich atmosphere, molecular absorption and scattering processes may result in detectable radius variations as a function of wavelength. The aim of this paper is to measure these variations. We have obtained observations of the transit of GJ1214b in the r- and I-band with the INT, in the g, r, i and z bands with the 2.2 meter MPI/ESO telescope, in the Ks-band with the NOT, and in the Kc-band with the WHT. By comparing the transit depth between the the different bands, which is a measure for the planet-to-star size ratio, the atmosphere is investigated. We do not detect clearly significant variations in the planet-to-star size ratio as function of wavelength. Although the ratio at the shortest measured wavelength, in g-band, is 2sigma larger than in the other bands. The uncertainties in the Ks and Kc bands are large, due to systematic features in the light curves. The tentative increase in the planet-to-star size ratio at the shortest wavelength could be a sign of an increase in the effective planet-size due to Rayleigh scattering, which would require GJ1214b to have a hydrogen-rich atmosphere. If true, then the atmosphere has to have both clouds, to suppress planet-size variations at red optical wavelengths, as well as a sub-solar metallicity, to suppress strong molecular features in the near- and mid-infrared. However, star spots, which are known to be present on the hoststar's surface, can (partly) cancel out the expected variations in planet-to-star size ratio, due to the lower surface temperature of the spots . A hypothetical spot-fraction of 10% would be able to raise the infrared points sufficiently with respect to the optical measurements to be inconsistent with a water-dominated atmosphere. [abridged]

Star not being cooperative I see.

Incidentally thread title is incorrect, it should be GJ 1214 b not Gliese 1214 b. The Catalog of Nearby Stars has several different sections, the original Gliese numbers are 1-999, numbers 1000 and up are from various extensions. GJ is applicable to the entire range, "Gliese" only for numbers below 1000.

As to threads, we seem to have several, might be nice to tie them up into one place:

J-band transits of GJ 1214b
Metals in the atmosphere of GJ 1214 b?

Lazarus wrote:

The Catalog of Nearby Stars has several different sections, the original Gliese numbers are 1-999, numbers 1000 and up are from various extensions. GJ is applicable to the entire range, "Gliese" only for numbers below 1000

Interesting! And excellent idea. I'll ammend the thread title and clean up the place a bit by merging those threads.

The Flat Transmission Spectrum of the Super-Earth GJ1214b from Wide Field Camera 3 on the Hubble Space Telescope

Quote :

Capitalizing on the observational advantage offered by its tiny M dwarf host, we present HST/WFC3 grism measurements of the transmission spectrum of the super-Earth exoplanet GJ1214b. These are the first published WFC3 observations of a transiting exoplanet atmosphere. After correcting for a ramp-like instrumental systematic, we achieve nearly photon-limited precision in these observations, finding the transmission spectrum of GJ1214b to be flat between 1.1 and 1.7 microns. Inconsistent with a cloud-free solar composition atmosphere at 8.2 sigma, the measured achromatic transit depth most likely implies a large mean molecular weight for GJ1214b's outer envelope. A dense atmosphere rules out bulk compositions for GJ1214b that explain its large radius by the presence of a very low density gas layer surrounding the planet. High-altitude clouds can alternatively explain the flat transmission spectrum, but they would need to be optically thick up to 10 mbar or consist of particles with a range of sizes approaching 1 micron in diameter.

One of the posters listed in the Kepler Science Conference booklet looks like it may be relevant here:

The Effect of Exotic Clouds on the Transmission Spectra of Transiting Super-Earths
C. V. Morley, J. J. Fortney, M. S. Marley, C. Visscher.

Apparently there is the possibility of clouds of potassium chloride, zinc sulphide and sodium sulphide in the atmosphere of the planet. Question is whether they would be sufficient to explain the spectra...

Press releases on the paper Mongo quoted.
http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=50076
http://hubblesite.org/newscenter/archive/releases/2012/13/full/

http://www.sciencedaily.com/releases/2012/02/120221103741.htm Water world with how deep ocean?

Argument in favour of a hydrogen-dominated atmosphere.
http://arxiv.org/abs/1203.1921

I wonder if there's going to be a similar kind of back-and-forth argument about the atmosphere of the first habitable zone exoplanet to be spectroscopically analysed. Most probably yes...

Interesting paper http://arxiv.org/pdf/1204.4453.pdf