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Icarus 204 2009 63 86 Contents lists available at ScienceDirect Icarus journal homepage www elsevier com locate icarus The formation and evolution of youthful gullies on Mars Gullies as the late stage phase of Mars most recent ice age James L Dickson James W Head Department of Geological Sciences Brown University Providence RI 02912 USA a r t i c l e i n f o Article history Received 22 January 2009 Revised 29 April 2009 Accepted 24 June 2009 Available online 27 June 2009 Keywords Mars Mars climate Mars surface Geological processes a b s t r a c t Gullies are extremely young erosional depositional systems on Mars that have been carved by an agent that was likely to have been comprised in part by liquid water Malin M C Edgett K S 2000 Evidence for recent groundwater seepage and surface runoff on Mars Science 288 2330 2335 McEwen A S et al 2007 A closer look at water related geologic activity on Mars Science 317 1706 1709 The strong latitude and orientation dependencies that have been documented for gullies require 1 a volatile near the surface and 2 that insolation is an important factor for forming gullies These constraints have led to two categories of interpretations for the source of the volatiles 1 liquid water at depth beneath the melting isotherm that erupts suddenly groundwater and 2 ice at the surface or within the uppermost layer of soil that melts during optimal insolation conditions surface near surface melting In this contribution we synthesize global hemispheric regional and local studies of gullies across Mars and outline the criteria that must be met by any successful explanation for the formation of gullies We further document trends in both hemispheres that emphasize the importance of top down melting of recent icerich deposits and the cold trapping of atmospherically derived H2O frost snow as important components in the formation of gullies This provides context for the incorporation of high resolution multi spectral and hyper spectral data from the

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