Mars Atmosphere Argon Density Measurement on Mer Mission

Introduction Using the Alpha Particle X-ray Spectrometer (APXS) (see Fig.1) on board Spirit and Opportunity rovers on MER mission, we were able to measure the argon density variation in the martian atmosphere as a function of seasonal changes. Due mainly to the variation of the temperature as a function of season on martian poles, the air mass on Mars is constantly moving from North pole to South pole in the summer, and vice versa in the winter on North pole. The freezing and melting of the CO2 in the martian atmosphere at the poles creates local atmospheric lows/highs that moves the air mass. The argon, however, due to its much lower freezing point, never freezes and stays in the air. An enhancement of Ar/CO2 mixing ratio by a factor of six at the martian South pole during the winter has been observed by the Gamma Ray Spectrometer onboard the Odyssey orbiter around Mars [1,2].