Theoretical spectra of terrestrial exoplanet surfaces
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 μm and 15-2...
| Main Authors: | , , |
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| Format: | Article |
| Language: | en_US |
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Institute of Physics Publishing
2012
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| Online Access: | http://hdl.handle.net/1721.1/74201 https://orcid.org/0000-0002-6892-6948 |
| _version_ | 1826208711004127232 |
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| author | Hu, Renyu Ehlmann, Bethany L. Seager, Sara |
| author2 | Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences |
| author_facet | Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences Hu, Renyu Ehlmann, Bethany L. Seager, Sara |
| author_sort | Hu, Renyu |
| collection | MIT |
| description | 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 μm and 15-25 μm. 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. |
| first_indexed | 2024-09-23T14:10:35Z |
| format | Article |
| id | mit-1721.1/74201 |
| institution | Massachusetts Institute of Technology |
| language | en_US |
| last_indexed | 2024-09-23T14:10:35Z |
| publishDate | 2012 |
| publisher | Institute of Physics Publishing |
| record_format | dspace |
| spelling | mit-1721.1/742012022-10-01T19:36:33Z Theoretical spectra of terrestrial exoplanet surfaces Hu, Renyu Ehlmann, Bethany L. Seager, Sara Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences Hu, Renyu Seager, Sara 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 μm and 15-25 μm. 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. United States. National Aeronautics and Space Administration (NASA Earth and Space Science Fellowship (NESSF/NNX11AP47H)) 2012-10-22T20:51:01Z 2012-10-22T20:51:01Z 2012-05 2012-02 Article http://purl.org/eprint/type/JournalArticle 0004-637X 1538-4357 http://hdl.handle.net/1721.1/74201 Hu, Renyu, Bethany L. Ehlmann, and Sara Seager. “THEORETICAL SPECTRA OF TERRESTRIAL EXOPLANET SURFACES.” The Astrophysical Journal 752.1 (2012): 7. Web. https://orcid.org/0000-0002-6892-6948 en_US http://dx.doi.org/ 10.1088/0004-637x/752/1/7 Astrophysical Journal Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. application/pdf Institute of Physics Publishing IOP |
| spellingShingle | Hu, Renyu Ehlmann, Bethany L. Seager, Sara Theoretical spectra of terrestrial exoplanet surfaces |
| title | Theoretical spectra of terrestrial exoplanet surfaces |
| title_full | Theoretical spectra of terrestrial exoplanet surfaces |
| title_fullStr | Theoretical spectra of terrestrial exoplanet surfaces |
| title_full_unstemmed | Theoretical spectra of terrestrial exoplanet surfaces |
| title_short | Theoretical spectra of terrestrial exoplanet surfaces |
| title_sort | theoretical spectra of terrestrial exoplanet surfaces |
| url | http://hdl.handle.net/1721.1/74201 https://orcid.org/0000-0002-6892-6948 |
| work_keys_str_mv | AT hurenyu theoreticalspectraofterrestrialexoplanetsurfaces AT ehlmannbethanyl theoreticalspectraofterrestrialexoplanetsurfaces AT seagersara theoreticalspectraofterrestrialexoplanetsurfaces |