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Spectroscopic characterization of the atmospheres of potentially habitable planets: GL 581 d as a model case study

von Paris, P. and Cabrera, J. and Godolt, M. and Grenfell, J. L. and Hedelt, P. and Rauer, Heike and Schreier, Franz and Stracke, Barbara (2011) Spectroscopic characterization of the atmospheres of potentially habitable planets: GL 581 d as a model case study. Astronomy and Astrophysics, 534 (A26), pp. 1-11. EDP Sciences. DOI: 10.1051/00046361/201117091. ISSN 0004-6361.

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Official URL: http://www.aanda.org/index.php?option=com_toc&url=/articles/aa/abs/2011/10/contents/contents.html

Abstract

Context. Were a potentially habitable planet to be discovered, the next step would be the search for an atmosphere and its characterization. Eventually, surface conditions, hence habitability, and biomarkers as indicators for life would be assessed. Aims. The super-Earth candidate Gliese (GL) 581 d is the first potentially habitable extrasolar planet so far discovered. Therefore, GL 581 d is used to illustrate a hypothetical detailed spectroscopic characterization of such planets. Methods. Atmospheric profiles for a wide range of possible one-dimensional (1D) radiative-convective model scenarios of GL 581 d were used to calculate high-resolution synthetic emission and transmission spectra. Atmospheres were assumed to be composed of N2, CO2, and H2O. From the spectra, signal-to-noise ratios (SNRs) were calculated for a telescope such as the planned James Webb Space Telescope (JWST). Exposure times were set to be equal to the duration of one transit. Results. The presence of the model atmospheres can be clearly inferred from the calculated synthetic spectra thanks to strong water and carbon-dioxide absorption bands. Surface temperatures can be inferred for model scenarios with optically thin spectral windows. Dense, CO2-rich (potentially habitable) scenarios do not enable us to determine the surface temperatures nor assess habitability. Degeneracies between CO2 concentration and surface pressure complicate the interpretation of the calculated spectra, hence the determination of atmospheric conditions. Still, inferring approximative CO2 concentrations and surface pressures is possible. In practice, detecting atmospheric signals is challenging because the calculated SNR values are well below unity in most of the cases. The SNR for a single transit was only barely larger than unity in some near-IR bands for transmission spectroscopy. Most interestingly, the false-positive detection of biomarker candidates such as methane and ozone might be possible in low resolution spectra because CO2 absorption bands overlap biomarker spectral bands. This can be avoided, however, by observing all main CO2 IR bands instead of concentrating on, e.g., the 4.3 or 15 μm bands only. Furthermore, a masking of ozone signatures by CO2 absorption bands is shown to be possible. Simulations imply that such a false-negative detection of ozone would be possible even for rather high ozone concentrations of up to 10-5.

Document Type:Article
Title:Spectroscopic characterization of the atmospheres of potentially habitable planets: GL 581 d as a model case study
Authors:
AuthorsInstitution or Email of Authors
von Paris, P.philip.vonparis@dlr.de
Cabrera, J.juan.cabrera@dlr.de
Godolt, M.TU Berlin
Grenfell, J. L.TU Berlin
Hedelt, P.University of Bordeaux, Bordeaux, France
Rauer, Heikeheike.rauer@dlr.de
Schreier, Franzfranz.schreier@dlr.de
Stracke, Barbarabarbara.stracke@dlr.de
Date:2011
Journal or Publication Title:Astronomy and Astrophysics
Refereed publication:Yes
In Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:534
DOI:10.1051/00046361/201117091
Page Range:pp. 1-11
Editors:
EditorsEmail
UNSPECIFIEDaanda.org
Publisher:EDP Sciences
Series Name:Planets and Planetary Systems
ISSN:0004-6361
Status:Published
Keywords:Atmospheres, Gliese 581 d, Habitability
HGF - Research field:Aeronautics, Space and Transport (old)
HGF - Program:Space (old)
HGF - Program Themes:W EW - Erforschung des Weltraums
DLR - Research area:Space
DLR - Program:W EW - Erforschung des Weltraums
DLR - Research theme (Project):W - Projekt COROT Beteiligung (old)
Location: Berlin-Adlershof , Oberpfaffenhofen
Institutes and Institutions:Remote Sensing Technology Institute > Atmospheric Processors
Institute of Planetary Research > Extrasolar Planets and Atmospheres
Deposited By: Joachim Wolfgang Stock
Deposited On:07 Nov 2011 09:06
Last Modified:08 May 2013 08:41

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