Journal Article

Background levels of methane in Mars’ atmosphere show strong seasonal variations

Glavin, Daniel P., Genzer, Maria, Atreya, Sushil K., Eigenbrode, Jennifer L., Smith, Christina L., Sutter, Brad, Keymeulen, Didier, Gomez-Elvira, Javier, Zorzano, Maria-Paz, Kahanpää, Henrik, McKay, Christopher P., Harri, Ari-Matti, Lemmon, Mark, Trainer, Melissa G., Mahaffy, Paul R., Gough, Raina V., Rafkin, Scot C. R., Zurek, Richard W., Meslin, Pierre-Yves, Crisp, Joy, Wong, Michael H., House, Christopher H., Navarro-Gonzalez, Rafael, Pavlov, Alexander, Schwenzer, Susanne P., Archer, Doug, Vicente-Retortillo, Álvaro, Flesch, Gregory J., Christensen, Lance E., Smith, Michael D., Steele, Andrew, Malespin, Charles, Coll, Patrice J., Hassler, Donald M., Moores, John E., Martinez, German, Martin-Torres, Javier, Viudez-Moreiras, Daniel, Pla-García, Jorge, Webster, Christopher R., Vasavada, Ashwin R., Pearson, John C., Sander, Stanley P., Freissinet, Caroline

2018

Overview

The Curiosity rover has been sampling on Mars for the past 5 years (see the Perspective by ten Kate). Eigenbrode et al. used two instruments in the SAM (Sample Analysis at Mars) suite to catch traces of complex organics preserved in 3-billion-year-old sediments. Heating the sediments released an array of organics and volatiles reminiscent of organic-rich sedimentary rock found on Earth. Most methane on Earth is produced by biological sources, but numerous abiotic processes have been proposed to explain martian methane. Webster et al. report atmospheric measurements of methane covering 3 martian years and found that the background level varies with the local seasons. The seasonal variation provides an important clue for determining the origin of martian methane. Science , this issue p. 1096 , p. 1093 ; see also p. 1068 The background level of methane in Mars’ atmosphere varies with season, providing a clue to its origin. Variable levels of methane in the martian atmosphere have eluded explanation partly because the measurements are not repeatable in time or location. We report in situ measurements at Gale crater made over a 5-year period by the Tunable Laser Spectrometer on the Curiosity rover. The background levels of methane have a mean value 0.41 ± 0.16 parts per billion by volume (ppbv) (95% confidence interval) and exhibit a strong, repeatable seasonal variation (0.24 to 0.65 ppbv). This variation is greater than that predicted from either ultraviolet degradation of impact-delivered organics on the surface or from the annual surface pressure cycle. The large seasonal variation in the background and occurrences of higher temporary spikes (~7 ppbv) are consistent with small localized sources of methane released from martian surface or subsurface reservoirs.

• Publisher: The American Association for the Advancement of Science,American Association for the Advancement of Science (AAAS)
• Subject: Atmosfärsvetenskap / Atmosphere / Atmospheric Science / Background levels / Confidence intervals / Curiosity (Mars rover) / Environment and Society / Environmental Sciences / In situ measurement / Mars / Mars atmosphere / Mars craters / Mars rovers / Mars surface / Measuring instruments / Methane / Personality Traits / Pressure / Seasonal variations / Sedimentary rocks / Sediments / Tunable lasers / Volatile compounds / Volatiles