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Detection of Molecular Hydrogen in the Atmosphere of Mars | Science

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Detection of Molecular Hydrogen in the Atmosphere of Mars

Vladimir A. Krasnopolsky and Paul D. FeldmanAuthors Info & Affiliations

Science

30 Nov 2001

Vol 294, Issue 5548

pp. 1914-1917

DOI: 10.1126/science.1065569

Abstract

Four hydrogen (H₂) lines have been detected in a spectrum of Mars observed with the Far Ultraviolet Spectroscopic Explorer. Three of those lines are excited by the solar Lyman β photons. The line intensities correspond to a column H₂ abundance of 1.17 (±0.13) × 10¹³ per square centimeter above 140 kilometers on Mars. A photochemical model for the upper atmosphere that simulates the observed H₂abundance results in an H₂ mixing ratio of 15 ± 5 parts per million in the lower atmosphere. The H₂ and HD mixing ratios agree with photochemical fractionation of D (deuterium) between H₂O and H₂. Analysis of D fractionation among a few reservoirs of ice, water vapor, and molecular hydrogen on Mars implies that a global ocean more than 30 meters deep was lost since the end of hydrodynamic escape. Only 4% of the initially accreted water remained on the planet at the end of hydrodynamic escape, and initially Mars could have had even more water (as a proportion of mass) than Earth.

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Supported by the NASA FUSE Guest Investigator Program. V.A.K. thanks A. Dalgarno for consultation.

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