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Formation of recent martian gullies through melting of extensive water-rich snow deposits


The observation of gullies on Mars indicates the presence of liquid water near the surface in recent times1,2, which is difficult to reconcile with the current cold climate. Gullies have been proposed to form through surface runoff from subsurface aquifers1,3 or through melting of near-surface ice under warmer conditions4. But these gullies are observed to occur preferentially in cold mid-latitudes2, where the presence of liquid water is less likely, and on isolated surfaces where groundwater seepage would not be expected, making both potential explanations unsatisfactory. Here I show that gullies can form by the melting of water-rich snow that has been transported from the poles to mid-latitudes during periods of high obliquity within the past 105 to 106 years (refs 5, 6). Melting within this snow7 can generate sufficient water to erode gullies in about 5,000 years. My proposed model for gully formation is consistent with the age and location of the gullies, and it explains the occurrence of liquid water in the cold mid-latitudes as well as on isolated surfaces. Remnants of the snowpacks are still present on mid-latitude, pole-facing slopes, and the recent or current occurrence of liquid water within them provides a potential abode for life.

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Figure 1: Examples of mid-latitude, pole-facing mantling materials and their curvilinear upper boundaries (arrows).
Figure 2: Detail of the appearance and curvilinear upper boundary (arrows) of pole-facing mantling materials located in Dao Valles.
Figure 3: THEMIS image showing gullies emerging from beneath and within a mantling snow unit where this unit is being removed.
Figure 4: MOC image of gullies with a remnant of the snow mantle (arrow) proposed to be the source of water that eroded these gullies.

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I thank the THEMIS instrument development team at Arizona State University and Raytheon Santa Barbara Remote Sensing, and the spacecraft development and operations teams at the Jet Propulsion Laboratory and Lockheed Martin Astronautics, for the development and performance of the THEMIS instrument and the Odyssey spacecraft. I also thank J. Rice, S. Ruff, H. Kieffer, M. Malin and B. Jakosky for discussions and contributions, and M. Carr and J. Mustard for comments that improved the original manuscript. This work was supported through the NASA Mars Odyssey Project and the NASA Mars Data Analysis Program.

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Correspondence to Philip R. Christensen.

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Christensen, P. Formation of recent martian gullies through melting of extensive water-rich snow deposits. Nature 422, 45–48 (2003).

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