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Is pi Men cs Atmosphere Hydrogen-dominated? Insights from a Non-detection of H I Ly alpha Absorption

Garcia Munoz, A. and Youngblood, A. and Fossati, L. and Gandolfi, D. and Cabrera Perez, Juan and Rauer, H (2020) Is pi Men cs Atmosphere Hydrogen-dominated? Insights from a Non-detection of H I Ly alpha Absorption. Astrophysical Journal Letters, 888 (2), L21. Institute of Physics (IOP) Publishing. doi: 10.3847/2041-8213/ab61ff. ISSN 2041-8205.

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Official URL: https://iopscience.iop.org/article/10.3847/2041-8213/ab61ff


Constraining the composition of super-Earth-to-sub-Neptune-sized planets is a priority in order to understand the processes of planetary formation and evolution. Pi Men c represents a unique target for the atmospheric and compositional characterization of such planets because it is strongly irradiated and its bulk density is consistent with abundant H2O. We searched for hydrogen from photodissociating H2/H2O in pi Men c s upper atmosphere through H i Ly alpha transmission spectroscopy with the Hubble Space Telescope Imaging Spectrograph, but did not detect it. We set 1 sigma (3 sigma) upper limits for the effective planet-to-star size ratio R Ly alpha /R sstarf = 0.13 (0.24) and 0.12 (0.20) at velocities [-215, -91] km s-1 and [+57, +180] km s-1, respectively. We reconstructed the stellar spectrum, and estimate that pi Men c receives about 1350 erg cm-2 s-1 of 5-912 Angstrom energy, enough to cause rapid atmospheric escape. An interesting scenario to explain the non-detection is that pi Men c s atmosphere is dominated by H2O or other heavy molecules rather than H2/He. According to our models, abundant oxygen results in less extended atmospheres, which transition from neutral to ionized hydrogen closer to the planet. We compare our non-detection to other detection attempts, and tentatively identify two behaviors: planets with densities lesssim2 g cm-3 (and likely hydrogen-dominated atmospheres) result in H i Ly alpha absorption, whereas planets with densities gsim3 g cm-3 (and plausibly non-hydrogen-dominated atmospheres) do not result in measurable absorption. Investigating a sample of strongly irradiated sub-Neptunes may provide some statistical confirmation if it is shown that they do not generally develop extended atmospheres.

Item URL in elib:https://elib.dlr.de/137206/
Document Type:Article
Title:Is pi Men cs Atmosphere Hydrogen-dominated? Insights from a Non-detection of H I Ly alpha Absorption
AuthorsInstitution or Email of AuthorsAuthor's ORCID iDORCID Put Code
Garcia Munoz, A.Zentrum fuer Astronomie und Astrophysik, Technische Universitaet Berlin, Germanyhttps://orcid.org/0000-0003-1756-4825UNSPECIFIED
Youngblood, A.NASA Goddard Space Flight Center, Greenbelt, MD 20771, USAhttps://orcid.org/0000-0002-1176-3391UNSPECIFIED
Fossati, L.Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz, Austriahttps://orcid.org/0000-0003-4426-9530UNSPECIFIED
Gandolfi, D.Dipartimento di Fisica, Università di Torino, via P. Giuria 1, I-10125 Torino, Italyhttps://orcid.org/0000-0001-8627-9628UNSPECIFIED
Cabrera Perez, JuanUNSPECIFIEDhttps://orcid.org/0000-0001-6653-5487UNSPECIFIED
Date:9 January 2020
Journal or Publication Title:Astrophysical Journal Letters
Refereed publication:Yes
Open Access:Yes
Gold Open Access:No
In ISI Web of Science:Yes
Page Range:L21
Publisher:Institute of Physics (IOP) Publishing
Keywords:Exoplanet atmospheres Aeronomy Ultraviolet astronomy Exoplanet atmospheric composition
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Space Exploration
DLR - Research area:Raumfahrt
DLR - Program:R EW - Space Exploration
DLR - Research theme (Project):R - Project PLATO (old)
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Planetary Research > Extrasolar Planets and Atmospheres
Institute of Planetary Research > Leitungsbereich PF
Deposited By: Cabrera Perez, Juan
Deposited On:06 Nov 2020 10:41
Last Modified:06 Nov 2020 10:41

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