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Seasonal Erosion and Restoration of Mars’ Northern Polar Dunes

Science  04 Feb 2011:
Vol. 331, Issue 6017, pp. 575-578
DOI: 10.1126/science.1197636

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  1. Fig. 1

    Slope streaks and a small cloud of dust (arrow) kicked up by sand and ice cascading down the dune slope are captured in this subimage acquired at 83.5°N, 118.6°E. Imaged at Ls = 55.7 (35), dunes are still covered by seasonal ice. This particular dune is ~40 m high. North is up; light is from the lower left. The dark slope streaks visible in the image are postulated to be sand that has been released from the brink of the dune to slide down and cover seasonal ice.

  2. Fig. 2

    A time-series of subimages, from left to right, at three sites in a field of transverse dunes at 84.7°N, 0.7°E shows that extensive erosion has taken place in one Mars year. The center false-color strip are subimages from ESP_016893_2650 taken on 4 March 2010, Ls = 59.6 when the region was still covered with seasonal CO2 ice. The black-and-white ice-free subimages compare PSP_009324_2650 (left subimage in each row), acquired on 23 July 2008, Ls = 102.4 in MY29, with ESP_017974_2650 (right subimage in each row) acquired on 28 May 2010, Ls = 96.6 in MY30, the second year of HiRISE monitoring. North is down; light is from the upper right. These subtle changes on dark dunes would have been very difficult to detect in past images without the SNR of HiRISE.

  3. Fig. 3

    This series acquired at 83.5N, 118.5 E illustrates sublimation activity and the redistribution of sand on the slipface. North is down in all images; sunlight is coming from the upper right. Slipfaces are oriented to the south in this dune field. (A) This subimage taken 15 September 2008 at Ls = 127.4 in the first year of HiRISE monitoring shows the ice-free dune. (B) A subimage acquired in the second year of HiRISE monitoring, 1 June 2010 at Ls = 98.7 after seasonal ice has sublimed, shows two new grainflows on the dune. (C) 14 January 2010 frosted subimage at Ls = 37.6 shows that sand has moved part of the way down the dune and appears to be blocked by a thin ledge of bright ice. Visible are cracks in the ice along the brink of the dune on the left side. Dark material on the stoss side of the dune may be patches of thin ice or dune material blown backward by the sublimation gas flow. (D) 5 February 2010, subimage at Ls = 47.7 shows that sand has moved further down the slipface. Other smaller slides are initiated at the crack in the ice along the brink of the dune. (E) 28 February 2010, Ls = 57.7. Sand has now started to accumulate at the foot of the slope, and other streaks are lengthening.

  4. Fig. 4

    The dune margin in MY29 image PSP_008968_2650 at 84.7°N, 0.7°E is compared with MY30 ESP_017895_2650.

  5. Fig. 5

    The white arrows point to a location on the brink of this dune at 84°N, 233°E that had no alcove in the first year of HiRISE operation (MY29) and experienced sublimation activity (middle), which resulted in the new alcove and fan (with total length of 120 m) in MY30. The layer of new material forming the apron is very thin; the original ripples have not been completely buried. Degradation of gullies is also occurring, as adjacent alcoves are being filled in, and ripples are already forming in the alcoves.