Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p53f..02h&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P53F-02
Physics
[5422] Planetary Sciences: Solid Surface Planets / Ices, [5462] Planetary Sciences: Solid Surface Planets / Polar Regions, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
The High Resolution Imaging Science Experiment (HiRISE) [1] on the Mars Reconnaissance Orbiter (MRO) has observed the north polar region during 3 summer seasons on Mars. Here we summarize analyses of the north polar data, focusing on active and recent processes including evolution of frost streaks, the north polar residual cap (NPRC), frost avalanches, and scarp erosion. Bright and dark streaks have been observed at the periphery of the NPRC by previous Mars orbiters and were the target of several HiRISE observations. Some of these HiRISE images indicate that formation of the streaks involves processes more complex than the emplacement of dark veneers proposed by Rodriguez et al. [2]. Bright and dark streaks are seen to evolve during the northern summer, evidence for active eolian redistribution of frost and perhaps darker (non-volatile) dust or sand. Based on MRO Context imager observations of craters on the NPRC, accumulation rates are estimated to be 4-5 mm/yr within these craters, with lower rates likely on the intracrater NPRC surface [3]. The observed crater population probably accumulated during the last 20 ka or less. It is likely that NPRC resurfacing is episodic rather than continuous, and that annual changes may be detectable at HiRISE image resolutions. Therefore, a campaign of HiRISE observations of four NPRC targets near 87°N latitude (the maximum latitude of the MRO ground track) was initiated during the Martian northern summer of 2008 and continued during the summer of 2010. The images acquired during this campaign, with nearly nadir viewing geometry and similar solar azimuth, are being searched for evidence for current redistribution of NPRC material. Analyses are ongoing; no changes have been detected to date. We also conducted an early- to mid-spring 2010 survey of circumpolar scarps to monitor for falls and avalanches of CO2 frost and dust, of the type discovered on a scarp in northern spring 2008 [4]. The results confirm the restriction of this activity to Ls ≈ 25-45° and revealed activity at additional scarps. Thermal modeling of the scarp environment assesses the relationship between avalanches, trigger mechanisms, and winter frost sublimation. A 2010 northern summer survey of steep scarps imaged in previous summers is documenting the frequency of mass-wasting of icy blocks of the layered deposits and basal layers and their contribution to polar landscape evolution. The HiRISE north polar imaging campaign demonstrates that surface materials are mobilized annually and that the north polar region is very active. Observations discussed here highlight the importance of both long- and short-term monitoring of north polar targets to further our understanding of time-variable phenomena in this region. References: [1] McEwen, A. S. et al. (2007) JGR 112, doi:10.1029/2005JE002605. [2] Rodriguez, J.A.P. et al. (2007) Mars 3, 29. [3] Banks, M. E. et al. (2010) JGR 115, E08006, doi:10.1029/2009JE003523. [4] Russell, P. S. et al. (2008) GRL 35, L23204, doi:10.1029/2008GL035790.
Banks Maria Elaine
Byrne Shane
Hansen Camilla Juul
Herkenhoff Ken E.
HiRISE Team
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