Mathematics – Logic
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmep51c0607a&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #EP51C-0607
Mathematics
Logic
[1826] Hydrology / Geomorphology: Hillslope, [5419] Planetary Sciences: Solid Surface Planets / Hydrology And Fluvial Processes, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
Current temperature and pressure conditions on Mars suggest that liquid water is unstable at the surface. However, features reminiscent of gullies on the Earth, generally consisting of alcoves, channels, and debris aprons, suggest liquid agents, water being the most plausible. Although not stable at the surface, models suggest liquid water is possible in the subsurface. Thus, mechanisms for gully formation include release of ground water from shallow or deep aquifers, although alternatives include snowpack or other near-surface meltwater sources, reservoirs of liquid CO2 or brine, or dry flows. Here, we characterize and classify gullies by morphology and distribution, using the Mars Reconnaissance Orbiter (MRO) Context (CTX) images, in order to assess possible mechanisms of gully formation. MRO CTX images provide wider views of craters in which gullies tend to be found than images by the Mars Orbiter Camera and HiRISE. Context images may thus eliminate observational bias that might result from narrower fields of view. We examine gully features that occur within craters on images acquired from the first six months of the Primary Science Phase of the MRO mission (P01-P06, November 2006 through April 2007), bounded by Mars Charts 24, 27 and 29, in the southern mid-latitudes (30-60ο S; 120-180ο W, 0-300ο W, and 180-240ο W, respectively). Representative gullies within morphologically distinct clusters are sampled. Preliminary results based on 118 craters, featuring 176 gully clusters, from MC 29 show features consistent with aquifer-based mechanisms inferred from gully alcoves that are abbreviated by horizontal geologic layering (30% of all gully clusters), and from gully clusters showing the alcove-to-channel transition aligned with the lower boundary of a geologic strata (48% of all gully clusters). Channels incise into aprons in 55% of gully clusters, and 18% of all channel types reveal levee-like features, also consistent with liquid aquifer models and meltwater-based mechanisms. Gully features consistent with the snowpack meltwater formation mechanism are inferred from gully clusters that are directly associated with pasted-on mantle material (25% of all gully clusters). Gully orientation and distribution patterns further suggest that obliquity driven models are also plausible, as suggested by preferential gully formation on northern, pole-facing slopes of craters found between 30-40ο S. Between 40-50ο S, gullies preferentially form on the southwestern face, potentially suggesting liquid-driven gullying as a result of diurnal heating differences. While no one hypothesis is readily supported or rejected as the sole gully formation mechanism, features consistent with shallow aquifer- and snowpack meltwater-based formation are more commonly observed.
Araki Sakae
Dombard Andrew J.
Williams Richard
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