Debris Flows on Mars: Correlation with Present Day Maximum Surface Pressures and Temperatures

Abstract

The observation of debris flows in high resolution MGS–MOC images suggests that liquid water was involved in their formation in the recent past. The fact that many debris flows on Mars start from the top of isolated peaks and from the crest of dunes favors an origin by melting of near–surface ice by solar heating. The minimum requirements for pure liquid water are surface pressures above 6.1 mbar and temperatures above 273 K. The surface pressure primarily depends on the topography. The 6.1 mbar pressure level on Mars occurs at a MOLA–topographic height of approximately –1600 m at LS=0°, but varies by 1.5–2.5 km within a Martian year over this mean value due to the annual CO2 condensation–sublimation cycle. Maximum surface pressures above 6.1 mbar can occur seasonally at MOLA topographic heights up to about 1000 m. To produce a global maximum ground temperature map we used the TES brightness temperature data. We identified nearly 420 MOC–images (AB–M23) with debris flow features. The distribution of debris flows correlates well with areas of maximum surface pressures above 6.1 mbar. Also in the southern hemisphere many local areas (mostly in craters) correlate with debris flows. The regions at latitudes between 27°S to 65°S in the southern hemisphere also correlate with the maximum temperatures above 273 K. The maximum pressures and temperatures in the southern hemisphere occur at the same time in spring/summer around LS=270°. Surface pressures in the northern hemisphere (>30°N) are mostly above 6.1 mbar during the entire year, but the maximum temperatures do not reach the melting point. The distribution of debris flows correlates well with areas where the minimum requirements for transient liquid water in the southern hemisphere at latitudes between 27°S to 65°S are met. Most debris flows on Mars occur in these latitudes. A detailed global and regional statistical analysis is still in progress and will be presented at the conference.