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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 730096.0, MPI für Astronomie / Publikationen_mpia
The effect of Lyman α radiation on mini-Neptune atmospheres around M stars: application to GJ 436b
Authors:Miguel, Y.; Kaltenegger, L.; Linsky, J. L.; Rugheimer, S.
Date of Publication (YYYY-MM-DD):2015
Title of Journal:Monthly Notices of the Royal Astronomical Society
Start Page:345
End Page:353
Audience:Not Specified
Abstract / Description:Mini-Neptunes orbiting M stars are a growing population of known exoplanets. Some of them are located very close to their host star, receiving large amounts of UV radiation. Many M stars emit strong chromospheric emission in the H I Lyman α line (Lyα) at 1215.67 Å, the brightest far-UV emission line. We show that the effect of incoming Lyα flux can significantly change the photochemistry of mini-Neptunes' atmospheres. We use GJ 436b as an example, considering different metallicities for its atmospheric composition. For solar composition, H2O-mixing ratios show the largest change because of Lyα radiation. H2O absorbs most of this radiation, thereby shielding CH4, whose dissociation is driven mainly by radiation at other far-UV wavelengths (˜1300 Å). H2O photolysis also affects other species in the atmosphere, including H, H2, CO2, CO, OH and O. For an atmosphere with high metallicity, H2O- and CO2-mixing ratios show the biggest change, thereby shielding CH4. Direct measurements of the UV flux of the host stars are important for understanding the photochemistry in exoplanets' atmospheres. This is crucial, especially in the region between 1 and 10-6 bars, which is the part of the atmosphere that generates most of the observable spectral features.
Free Keywords:planets and satellites: atmospheres; planets and satellites: general; planets and satellites: individual: GJ 436b
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
Identifiers:ISSN:0035-8711 %R 10.1093/mnras/stu2107
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