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Title: THEORETICAL SPECTRA OF TERRESTRIAL EXOPLANET SURFACES

Abstract

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 7-13 {mu}m and 15-25 {mu}m. 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{sub g}(K) - A{sub g}(J)): A{sub g}(K) - A{sub 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{sub g}(K) - A{sub 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 extantmore » 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.« less

Authors:
;  [1]
  1. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)
Publication Date:
OSTI Identifier:
22037130
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 752; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION SPECTROSCOPY; ALBEDO; ASTRONOMY; ASTROPHYSICS; BRIGHTNESS; ICE; INFRARED SPECTRA; LAVA; MAGMA; MOLECULES; OLIVINE; PHOTON EMISSION; PLANETARY ATMOSPHERES; PLANETS; REFLECTION; SILICATES; SPECTROPHOTOMETRY; SURFACES

Citation Formats

Renyu, Hu, Seager, Sara, and Ehlmann, Bethany L., E-mail: hury@mit.edu. THEORETICAL SPECTRA OF TERRESTRIAL EXOPLANET SURFACES. United States: N. p., 2012. Web. doi:10.1088/0004-637X/752/1/7.
Renyu, Hu, Seager, Sara, & Ehlmann, Bethany L., E-mail: hury@mit.edu. THEORETICAL SPECTRA OF TERRESTRIAL EXOPLANET SURFACES. United States. https://doi.org/10.1088/0004-637X/752/1/7
Renyu, Hu, Seager, Sara, and Ehlmann, Bethany L., E-mail: hury@mit.edu. 2012. "THEORETICAL SPECTRA OF TERRESTRIAL EXOPLANET SURFACES". United States. https://doi.org/10.1088/0004-637X/752/1/7.
@article{osti_22037130,
title = {THEORETICAL SPECTRA OF TERRESTRIAL EXOPLANET SURFACES},
author = {Renyu, Hu and Seager, Sara and Ehlmann, Bethany L., E-mail: hury@mit.edu},
abstractNote = {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 7-13 {mu}m and 15-25 {mu}m. 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{sub g}(K) - A{sub g}(J)): A{sub g}(K) - A{sub 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{sub g}(K) - A{sub 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.},
doi = {10.1088/0004-637X/752/1/7},
url = {https://www.osti.gov/biblio/22037130}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 752,
place = {United States},
year = {Sun Jun 10 00:00:00 EDT 2012},
month = {Sun Jun 10 00:00:00 EDT 2012}
}