Abstract
Neptune-sized extrasolar planets that orbit relatively close to their host stars - often called "hot Neptunes" - are common within the known population of exoplanets and planetary candidates. Similar to our own Uranus and Neptune, inefficient accretion of nebular gas is expected produce hot Neptunes whose masses are dominated by elements heavier than hydrogen and helium. At high atmospheric metallicities of 10-10,000 times solar, hot Neptunes will exhibit an interesting continuum of atmospheric compositions, ranging from more Neptune-like, H2-dominated atmospheres to more Venus-like, CO 2-dominated atmospheres. We explore the predicted equilibrium and disequilibrium chemistry of generic hot Neptunes and find that the atmospheric composition varies strongly as a function of temperature and bulk atmospheric properties such as metallicity and the C/O ratio. Relatively exotic H 2O, CO, CO2, and even O2-dominated atmospheres are possible for hot Neptunes. We apply our models to the case of GJ 436b, where we find that a CO-rich, CH4-poor atmosphere can be a natural consequence of a very high atmospheric metallicity. From comparisons of our results with Spitzer eclipse data for GJ 436b, we conclude that although the spectral fit from the high-metallicity forward models is not quite as good as the best fit obtained from pure retrieval methods, the atmospheric composition predicted by these forward models is more physically and chemically plausible in terms of the relative abundance of major constituents. High-metallicity atmospheres (orders of magnitude in excess of solar) should therefore be considered as a possibility for GJ 436b and other hot Neptunes.
| Original language | English (US) |
|---|---|
| Article number | 34 |
| Journal | Astrophysical Journal |
| Volume | 777 |
| Issue number | 1 |
| DOIs | |
| State | Published - Nov 1 2013 |
| Externally published | Yes |
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Keywords
- planetary systems
- planets and satellites: atmospheres
- planets and satellites: composition
- planets and satellites: individual (GJ 436b) stars: individual (GJ 436b)
ASJC Scopus subject areas
- Space and Planetary Science
- Astronomy and Astrophysics
Cite this
Compositional diversity in the atmospheres of hot neptunes, with application to GJ 436b. / Moses, J. I.; Line, M. R.; Visscher, C.; Richardson, M. R.; Nettelmann, N.; Fortney, J. J.; Barman, Travis S; Stevenson, K. B.; Madhusudhan, N.
In: Astrophysical Journal, Vol. 777, No. 1, 34, 01.11.2013.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Compositional diversity in the atmospheres of hot neptunes, with application to GJ 436b
AU - Moses, J. I.
AU - Line, M. R.
AU - Visscher, C.
AU - Richardson, M. R.
AU - Nettelmann, N.
AU - Fortney, J. J.
AU - Barman, Travis S
AU - Stevenson, K. B.
AU - Madhusudhan, N.
PY - 2013/11/1
Y1 - 2013/11/1
N2 - Neptune-sized extrasolar planets that orbit relatively close to their host stars - often called "hot Neptunes" - are common within the known population of exoplanets and planetary candidates. Similar to our own Uranus and Neptune, inefficient accretion of nebular gas is expected produce hot Neptunes whose masses are dominated by elements heavier than hydrogen and helium. At high atmospheric metallicities of 10-10,000 times solar, hot Neptunes will exhibit an interesting continuum of atmospheric compositions, ranging from more Neptune-like, H2-dominated atmospheres to more Venus-like, CO 2-dominated atmospheres. We explore the predicted equilibrium and disequilibrium chemistry of generic hot Neptunes and find that the atmospheric composition varies strongly as a function of temperature and bulk atmospheric properties such as metallicity and the C/O ratio. Relatively exotic H 2O, CO, CO2, and even O2-dominated atmospheres are possible for hot Neptunes. We apply our models to the case of GJ 436b, where we find that a CO-rich, CH4-poor atmosphere can be a natural consequence of a very high atmospheric metallicity. From comparisons of our results with Spitzer eclipse data for GJ 436b, we conclude that although the spectral fit from the high-metallicity forward models is not quite as good as the best fit obtained from pure retrieval methods, the atmospheric composition predicted by these forward models is more physically and chemically plausible in terms of the relative abundance of major constituents. High-metallicity atmospheres (orders of magnitude in excess of solar) should therefore be considered as a possibility for GJ 436b and other hot Neptunes.
AB - Neptune-sized extrasolar planets that orbit relatively close to their host stars - often called "hot Neptunes" - are common within the known population of exoplanets and planetary candidates. Similar to our own Uranus and Neptune, inefficient accretion of nebular gas is expected produce hot Neptunes whose masses are dominated by elements heavier than hydrogen and helium. At high atmospheric metallicities of 10-10,000 times solar, hot Neptunes will exhibit an interesting continuum of atmospheric compositions, ranging from more Neptune-like, H2-dominated atmospheres to more Venus-like, CO 2-dominated atmospheres. We explore the predicted equilibrium and disequilibrium chemistry of generic hot Neptunes and find that the atmospheric composition varies strongly as a function of temperature and bulk atmospheric properties such as metallicity and the C/O ratio. Relatively exotic H 2O, CO, CO2, and even O2-dominated atmospheres are possible for hot Neptunes. We apply our models to the case of GJ 436b, where we find that a CO-rich, CH4-poor atmosphere can be a natural consequence of a very high atmospheric metallicity. From comparisons of our results with Spitzer eclipse data for GJ 436b, we conclude that although the spectral fit from the high-metallicity forward models is not quite as good as the best fit obtained from pure retrieval methods, the atmospheric composition predicted by these forward models is more physically and chemically plausible in terms of the relative abundance of major constituents. High-metallicity atmospheres (orders of magnitude in excess of solar) should therefore be considered as a possibility for GJ 436b and other hot Neptunes.
KW - planetary systems
KW - planets and satellites: atmospheres
KW - planets and satellites: composition
KW - planets and satellites: individual (GJ 436b) stars: individual (GJ 436b)
UR - http://www.scopus.com/inward/record.url?scp=84886875594&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84886875594&partnerID=8YFLogxK
U2 - 10.1088/0004-637X/777/1/34
DO - 10.1088/0004-637X/777/1/34
M3 - Article
AN - SCOPUS:84886875594
VL - 777
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 1
M1 - 34
ER -