Observations of water vapour anomaly above Tharsis volcanos on Mars in the ISM (Phobos-2) experiment.

Abstract

Observations of Mars with the infrared imaging spectrometer ISM on board the Phobos-2 spacecraft provided more than 40,000 spectra in the wavelength range 0.7 - 3.2 muem with a spatial resolution of about 20 km. These spectra bear features of both atmospheric and surface origin. Measurements in the water vapour bands near 1.9 and 2.6 muem along the flanks of huge Martian volcanos provided the data on the H2O spatial variations above them. The retrieved mixing ratio was about 200 ppm above the volcanos, which was about a factor of five higher than that found above the surrounding terrains. The origin of the observed water vapour anomaly is likely to be connectedto the volcanos and could be explained by the regolith-atmosphere water vapour exchange. On the basis of a new theoretical approach to the process of diffusion of adsorbed water from the regolith to the atmosphere, a model of the observed anomaly was proposed. It implies an intensive vapour desorption during the day hours from the volcanic regolith which was assumed to be different in composition from that of surrounding highlands.