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Theoretical Spectra of Terrestrial Exoplanet Surfaces

Hu, Renyu and Ehlmann, Bethany L. and Seager, Sara (2012) Theoretical Spectra of Terrestrial Exoplanet Surfaces. Astrophysical Journal, 752 (1). Art. No. 7. ISSN 0004-637X.

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We investigate spectra of airless rocky exoplanets with a theoretical framework that self-consistently treats reflection and thermal emission. We find that a silicate surface on an exoplanet is spectroscopically detectable via prominent Si–O features in the thermal emission bands of 7–13μm and 15–25μm. The variation of brightness temperature due to the silicate features can be up to 20 K for an airless Earth analog, and the silicate features are wide enough to be distinguished from atmospheric features with relatively high resolution spectra. The surface characterization thus provides a method to unambiguously identify a rocky exoplanet. Furthermore, identification of specific rocky surface types is possible with the planet’s reflectance spectrum in near-infrared broad bands. A key parameter to observe is the difference between K-band and J-band geometric albedos (A(_g)(K) − A(_g)(J)): A(_g)(K) − A(_g)(J) > 0.2 indicates that more than half of the planet’s surface has abundant mafic minerals, such as olivine and pyroxene, in other words primary crust from a magma ocean or high-temperature lavas; A(_g)(K) − A(_g)(J) < −0.09 indicates that more than half of the planet’s surface is covered or partially covered by water ice or hydrated silicates, implying extant or past water on its surface. Also, surface water ice can be specifically distinguished by an H-band geometric albedo lower than the J-band geometric albedo. The surface features can be distinguished from possible atmospheric features with molecule identification of atmospheric species by transmission spectroscopy. We therefore propose that mid-infrared spectroscopy of exoplanets may detect rocky surfaces, and near-infrared spectrophotometry may identify ultramafic surfaces, hydrated surfaces, and water ice.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Hu, Renyu0000-0003-2215-8485
Ehlmann, Bethany L.0000-0002-2745-3240
Seager, Sara0000-0002-6892-6948
Additional Information:© 2012 The American Astronomical Society. Received 2012 February 15; accepted 2012 April 5; published 2012 May 18. Thanks to P. Isaacson for providing M3 lunar spectra and W. Calvin for providing modeled water ice spectra. R.H. is supported by NASA Earth and Space Science Fellowship (NESSF/NNX11AP47H).
Funding AgencyGrant Number
NASA Earth and Space Science FellowshipNNX11AP47H
Subject Keywords:atmospheric effects; planets and satellites: general; techniques: photometric; techniques: spectroscopic
Issue or Number:1
Record Number:CaltechAUTHORS:20120716-142432888
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Official Citation:Theoretical Spectra of Terrestrial Exoplanet Surfaces Renyu Hu et al. 2012 ApJ 752 7
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:32483
Deposited By: Aucoeur Ngo
Deposited On:16 Jul 2012 21:41
Last Modified:28 Oct 2019 23:42

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