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|Title:||Stringent upper limit of CH4 on Mars based on SOFIA/EXES observations||Authors:||Aoki, S.
Richter, M. J.
Vandaele, A. C.
Greathouse, T. K.
|Issue Date:||2018||Journal:||ASTRONOMY & ASTROPHYSICS||Number:||610||First Page:||A78||Abstract:||Discovery of CH<SUB>4</SUB> in the Martian atmosphere has led to much discussion since it could be a signature of biological and/or geological activities on Mars. However, the presence of CH<SUB>4</SUB> and its temporal and spatial variations are still under discussion because of the large uncertainties embedded in the previous observations. We performed sensitive measurements of Martian CH<SUB>4</SUB> by using the Echelon-Cross-Echelle Spectrograph (EXES) onboard the Stratospheric Observatory for Infrared Astronomy (SOFIA) on 16 March 2016, which corresponds to summer (Ls = 123.2<SUP>∘</SUP>) in the northern hemisphere on Mars. The high altitude of SOFIA ( 13.7 km) enables us to significantly reduce the effects of terrestrial atmosphere. Thanks to this, SOFIA/EXES improves our chances of detecting Martian CH<SUB>4</SUB> lines because it reduces the impact of telluric CH<SUB>4</SUB> on Martian CH<SUB>4</SUB>, and allows us to use CH<SUB>4</SUB> lines in the 7.5 μm band which has less contamination. However, our results show no unambiguous detection of Martian CH<SUB>4</SUB>. The Martian disk was spatially resolved into 3 × 3 areas, and the upper limits on the CH<SUB>4</SUB> volume mixing ratio range from 1 to 9 ppb across the Martian atmosphere, which is significantly less than detections in several other studies. These results emphasize that release of CH<SUB>4</SUB> on Mars is sporadic and/or localized if the process is present.||URI:||http://hdl.handle.net/20.500.12386/27906||URL:||https://www.aanda.org/articles/aa/abs/2018/02/aa30903-17/aa30903-17.html||ISSN:||0004-6361||DOI:||10.1051/0004-6361/201730903||Bibcode ADS:||2018A&A...610A..78A||Fulltext:||open|
|Appears in Collections:||1.01 Articoli in rivista|
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checked on Jan 19, 2021
checked on Jan 19, 2021
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