Fog phenomena on Mars

Abstract

Mars Express High Resolution Stereo Camera (HRSC) images show impressive morning fog features in Valles Marineris and other regions of the surface of Mars. Temperatures have been determined, simultaneously to the imaging, by Mars Express Planetary Fourier Spectrometer (PFS). This identifies water ice rather than frozen CO 2 as the cause of the fog observations in Valles Marineris. Numerical estimates of the water vapor pressure, and the related atmospheric water content, at the frost-point (temperature of freezing or “re-sublimation” of water vapor) by a 1-dimensional planetary boundary layer model indicate that conditions in the planetary boundary layer can indeed temporarily favor the formation of ice particles. A systematic registration of sites of fog observations shows preferred regions and seasons on Mars for fog phenomena. In the first instance, the fog phenomena seem to be induced or supported by orographic effects but not directly by the distribution pattern of the atmospheric vapor or by the regional subsurface water content. This paper documents and thermodynamically verifies the existence of fog of water ice particles in the near-surface atmosphere of Mars.