Journal
JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS
Volume 124, Issue 11, Pages 3000-3024Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1029/2019JE006175
Keywords
atmospheric composition; Mars atmosphere; Mars seasonal cycle; Mars Science Laboratory; sample analysis at Mars
Categories
Funding
- Programme National de Planetologie (PNP)
- Universidad Nacional Autonoma de Mexico [PAPIIT IN111619]
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The Sample Analysis at Mars (SAM) instrument onboard the Mars Science Laboratory Curiosity rover measures the chemical composition of major atmospheric species (CO2, N-2, Ar-40, O-2, and CO) through a dedicated atmospheric inlet. We report here measurements of volume mixing ratios in Gale Crater using the SAM quadrupole mass spectrometer, obtained over a period of nearly 5 years (3 Mars years) from landing. The observation period spans the northern summer of MY 31 and solar longitude (L-S) of 175 degrees through spring of MY 34, L-S = 12 degrees. This work expands upon prior reports of the mixing ratios measured by SAM QMS in the first 105 sols of the mission. The SAM QMS atmospheric measurements were taken periodically, with a cumulative coverage of four or five experiments per season on Mars. Major observations include the seasonal cycle of CO2, N-2, and Ar, which lags approximately 20-40 degrees of L-S behind the pressure cycle driven by CO2 condensation and sublimation from the winter poles. This seasonal cycle indicates that transport occurs on faster timescales than mixing. The mixing ratio of O-2 shows significant seasonal and interannual variability, suggesting an unknown atmospheric or surface process at work. The O-2 measurements are compared to several parameters, including dust optical depth and trace CH4 measurements by Curiosity. We derive annual mean volume mixing ratios for the atmosphere in Gale Crater: CO2 = 0.951 (+/- 0.003), N-2 = 0.0259 (+/- 0.0006), Ar-40 = 0.0194 (+/- 0.0004), O-2 = 1.61 (+/- 0.09) x 10(-3), and CO = 5.8 (+/- 0.8) x 10(-4).
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