Examinando por Autor "Atreya, S. K."

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Acceso Abierto
Day-night differences in Mars methane suggest nighttime containment at Gale crater
(EDP Sciences, 2021-06-29) Webster, C. R.; Mahaffy, Paul R.; Pla García, J.; Rafkin, S. C. R.; Moores, J. E.; Atreya, S. K.; Flesch, G. J.; Malespin, C. A.; Teinturier, S. M.; Kalucha, H.; Smith, C. L.; Viúdez Moreiras, Daniel; Vasavada, A. R.; Agencia Estatal de Investigación (AEI)
We report new measurements of atmospheric methane by the Curiosity rover’s Tunable Laser Spectrometer that is part of the Sample Analysis at Mars suite (TLS-SAM), finding nondetections during two daytime measurements of average value 0.05 ± 0.22 ppbv (95% confidence interval CI). These are in marked contrast with nighttime background levels of 0.52 ± 0.10 (95% CI) from four measurements taken during the same season of northern summer. This large day-night difference suggests that methane accumulates while contained near the surface at night, but drops below TLS-SAM detection limits during the day, consistent with the daytime nondetection by instruments on board the ExoMars Trace Gas Orbiter. With no evidence for methane production by the rover itself, we propose that the source is one of planetary micro-seepage. Dynamical modeling indicates that such methane release is contained within the collapsed planetary boundary layer (PBL) at night due to a combination of nocturnal inversion and convergent downslope flow winds that confine the methane inside the crater close to the point where it is released. The methane abundance is then diluted during the day through increased vertical mixing associated with a higher altitude PBL and divergent upslope flow that advects methane out of the crater region. We also report detection of a large spike of methane in June 2019 with a mean in situ value over a two-hour ingest of 20.5 ± 4 ppbv (95% CI). If near-surface production is occurring widely across Mars, it must be accompanied by a fast methane destruction or sequestration mechanism, or both.
Acceso Abierto
Seasonal Variations in Atmospheric Composition as Measured in Gale Crater, Mars
(American Geophysical Union: Advancing Earth and Space Science, 2019-11-12) Trainer, M. G.; Wong, M. H.; McConnochie, T. H.; Franz, H. B.; Atreya, S. K.; Conrad, Pamela G.; Lefèvre, F.; Mahaffy, Paul R.; Malespin, C. A.; Manning, H. L. K.; Martín Torres, Javier; Martínez, G. M.; McKay, C. P.; Navarro González, R.; Vicente Retortillo, Á.; Webster, C. R.; Zorzano, María Paz; Universidad Nacional Autónoma de México (UNAM); Zorzano, M. P. [0000-0002-4492-9650]; Navarro González, R. [0000-0002-6078-7621]; Martín Torres, J. [0000-0001-6479-2236]; Vicente Retortillo, A. [0000-0002-4553-7624]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
The Sample Analysis at Mars (SAM) instrument onboard the Mars Science Laboratory Curiosity rover measures the chemical composition of major atmospheric species (CO2, N2, 40Ar, O2, 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 (LS) of 175° through spring of MY 34, LS = 12°. 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, N2, and Ar, which lags approximately 20–40° of LS 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 O2 shows significant seasonal and interannual variability, suggesting an unknown atmospheric or surface process at work. The O2 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), N2 = 0.0259 (±0.0006), 40Ar = 0.0194 (±0.0004), O2 = 1.61 (±0.09) x 10‐3, and CO = 5.8 (±0.8) x 10‐4.