Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p34a..03d&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P34A-03
Physics
5400 Planetary Sciences: Solid Surface Planets, 5415 Erosion And Weathering, 5419 Hydrology And Fluvial Processes, 5422 Ices, 5464 Remote Sensing
Scientific paper
Martian gullies provide evidence for surface flow of liquid water in the last several million years, which has been difficult to reconcile with the low-temperature/low-pressure conditions observed today. Several global, hemispheric, and regional surveys of Mars Global Surveyor, Mars Odyssey, and Mars Express data have revealed the three-dimensional distribution of these features across the planet and have shown that gullies only form in regions conducive to the deposition, accumulation and preservation of atmospherically-emplaced water in the form of snow, frost, or ground-ice. Two primary hypotheses have persisted: that ground ice serves as a dam for a sequestered aquifer at depth which is released suddenly, or that ground ice, snow, and surface frost melt at the surface or within the active layer. Multi-spectral data from Mars Reconnaissance Orbiter reveal that (1) gullies are episodic systems, which demands that any model for gully formation provides a recharge mechanism; (2) cold-trapping of condensed volatiles occurs at the alcove/channel level; (3) gullies form at the same locations as features plausibly interpreted to represent previous episodes of ice-related flow; and (4) gully channels frequently emanate from the crest of gully alcoves instead of the base, showing that alcove generation is not necessarily a product of undermining and collapse at these locations. These new data change the scope of the gully debate: any model for gully formation must also account for the evolution of gully systems over time. We argue that gullies occur within the temporal context of orbitally-induced transport of ice from the poles to the mid-latitudes and back, and that gullies represent the final stages of this recession as water ice became less stable in the mid-latitudes. This provides an end-to-end model for gully initiation and reactivation that bears little dependence on subsurface stratigraphy, and is instead governed by localized cold traps within micro-climates that provide the only places on Mars conducive to the preservation and melting of snow/frost within the last few million years. This is consistent with the majority of gully systems on Earth, with the low-temperature and low- pressure climate of Mars generating short channel systems that terminate on steep slopes, consistent with observations of martian gullies to date.
Dickson James L.
Head James W.
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