Debris Flows on Mars: Global Distribution and Their Correlation to Present Day Maximum Surface Pressures and Temperatures

Introduction: The observation of debris flows in high resolution MGS–MOC images suggests that liquid water was involved in their formation in the recent past [1]. The fact that many debris flows on Mars start from the top of isolated peaks [2, 3] and from the crest of dunes [4, 5, 6] 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. Haberle et al. [7] tested the distribution of the debris flows against these minimum requirements using a general circulation model (GCM). They found no correlation mainly because of the low pressures in the southern hemisphere. Methods: 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 L S=0°, but varies by 1.5–2.5 km within a Martian year over this mean value [8] due to the annual CO2 condensation–sublimation cycle [9]. Maximum surface pressures above 6.1 mbar can occur seasonally at MOLA topographic heights up to about 1000 m. Figure 1 shows a global MOLA–topographic map with a resolution at 1/128 degrees per pixel (463 m/pixel). Elevations lower as 1000 m are shaded in gray, higher elevations where 6.1 mbar are not reached are white. To produce a global maximum ground temperature map we used the TES brightness temperature data [10]. Only brightness temperatures above 273 K and nadir measurements (<1°) were used. The temperature values were binned to a 12 km global grid using the maximum temperature value of each bin (Fig. 2). Correlation with debris flows: 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 (Fig. 1). Also in the southern hemisphere many local areas (mostly in craters) correlate with debris flows (a detailed statistical analysis is in preparation). These confined regions are in contrast to the GCM results [7], but explainable by the low horizontal resolution (7.5° x 9.0°) of the model and the high resolution MOLA–grid (1/128 degree). These regions at latitudes between 27°S to 65°S (except high southern latitudes >65°S) in the southern hemisphere also correlate with the maximum temperatures above 273 K (Fig. 2). The maximum pressures and temperatures in