Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p14c..01m&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P14C-01
Physics
[5415] Planetary Sciences: Solid Surface Planets / Erosion And Weathering, [5418] Planetary Sciences: Solid Surface Planets / Heat Flow, [5470] Planetary Sciences: Solid Surface Planets / Surface Materials And Properties
Scientific paper
Thermally-driven expansion and contraction is an ever-present, active process on Earth that contributes to the mechanical breakdown of rocks. It is also active on surfaces that lack atmospheres, though the scale of the process may differ in each case. On Earth, diurnal temperature oscillations cause macroscopic fractures and lower material strengths through thermal stress fatigue. Wind fluctuations in the terrestrial atmosphere cause high frequency temperature oscillations that contribute to surface breakdown through spalling and granular disintegration. Between these scales, however, the atmosphere acts to dampen the efficacy of heating and cooling. On airless bodies, this dampening effect is removed and temperature change rates increase dramatically. A commonly quoted threshold for dT/dt, above which permanent deformation is possible, is 2 K/min. This value is not well defined, as it is dependent on rock size, nature, structure, and temperature. We utilize thermal models of the Lunar and Mercurian surfaces to investigate the magnitude of dT/dt. Although these bodies are slowly rotating, sudden temperature changes are possible when shadows are cast over terrain of interest. To test the maximum efficiency of this process we expose surfaces to sunlight at local noon, and shadow them shortly afterwards. Preliminary results yield maximum dT/dt values of 0.58 and 6.2 K/min for regolith on the Moon and Mercury, respectively. For an exposed surface free of regolith, the values are 0.42 and 4.8 K/min, respectively. The values for Mercury are well above the established damage threshold, suggesting that thermal weathering can efficiently break down rocks on its surface. For the Moon, dT/dt values are below the threshold, but still of considerable magnitude. Given the uncertainty of the damage threshold, it is possible that Lunar dT/dt values may still contribute to rock breakdown. We will report on the results of more sophisticated models that track temperature changes over cratered landscapes, further investigation into the effects of rock properties on dT/dt thresholds, and resulting implications on the evolution of the Lunar and Mercurian surfaces.
Byrne Shane
Molaro J. L.
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