Atmospheric Measurements by Curiosity – An Overview

Abstract:

The abundances, seasonal variations and isotopic ratios of atmospheric constituents measured by Curiosity have provided important insight into the present and past history of Mars. The argon mixing ratio is found to have a relatively small seasonal change at the near-equatorial site of Curiosity, unlike the much larger changes detected previously at high polar latitudes in the winter and attributed to the annual deposition and sublimation of CO₂ at the martian poles. The Ar/N₂ ratio remains constant over seasons, as expected for non-condensible species.

On the other hand, methane, another non-condensible species, shows episodic spikes in mixing ratio but no particular seasonal trend with the measurements in hand. We will give an update of the data and possible scenarios of the formation and loss of this important species.

The atmospheric isotope ratios of argon (primordial and radiogenic), nitrogen, carbon dioxide and water vapor measured on Curiosity all point to a warmer and wetter Mars compared to its present cold and arid state. The D/H ratio measured in the fines drilled from a 3+ Gyr old mudstone give an unprecedented look into the evolution of water loss from early Mars. Complementary observations of contemporary D/H from ground-based telescopes further reinforce the view of substantial liquid water on the surface of Mars in the past.

Whereas the abovementioned isotope ratios are a good indicator of the evolutionary history of Mars in the past 4 billion years, the isotope ratios of the heavy noble gases, especially xenon, measured on Curiosity provide a better understanding of the very earliest periods when a massive loss of atmosphere took place by hydrodynamic escape or blowoff.