Constraints on Amazonian Climate from the Mars Exploration Rover Landing Sites

Details Constraints on Amazonian Climate from the Mars Exploration Rover Landing Sites Constraints on Amazonian Climate from the Mars Exploration Rover Landing Sites

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.p34a..01g&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #P34A-01

Other

5405 Atmospheres (0343, 1060), 5415 Erosion And Weathering, 6225 Mars

Scientific paper

The derivation of erosion rates from the surficial geology of the Gusev cratered plains and Meridiani Planum argues that the surfaces formed in a dry and desiccating environment similar to today's that was active throughout the Amazonian. The Late Hesperian/Early Amazonian cratered plains of Gusev crater that Spirit has traversed (exclusive of the Columbia Hills) are dominated by impact craters filled with soil, called hollows. Eolian bedforms appear to be presently inactive ripples and no active sand dunes have been identified. Moderate localized surface deflation of 5-25 cm is indicated by two-toned rocks with a redder patination along the base, ventifacts that originate from a common horizon above the soil, rocks that appear to be perched on top of other rocks, some undercut rocks, and the widespread pebble rich (desert lag) surface. The observed gradation and deflation of ejected fines and deposition in craters to form hollows thus provides a measure of the rate of erosion or redistribution (average vertical removal of material per unit time), which yields extremely slow erosion rates of ~0.03 nm/yr comparable to those estimated at the Mars Pathfinder (~0.01 nm/yr) and Viking 1 (~1 nm/yr) landing sites and argues that a dry and desiccating environment similar to today's has been active throughout the Hesperian and Amazonian (since ~3.7 Ga). The eolian erosion and degradation of Amazonian impact craters visited by Opportunity, the concentration of hematite spherules on the surface, and the inferred erosion of Hesperian craters all suggest slow eolian erosion rates of order 3 nm/yr by the sand sheet in the Hesperian and Amazonian. These erosion rates are 3-5 orders of magnitude lower than those estimated from erosion of Noachian terrain and craters, which are comparable to slow denudation rates on the Earth (>5 micron/yr) that are dominated by liquid water and are roughly coeval with a variety of geomorphic indicators (valley networks, degraded craters and highly eroded terrain) as well as the Noachian 'dirty' evaporites discovered by Opportunity that are from a wetter and likely warmer environment. The erosion rates from Gusev as well as those from Viking 1 and Pathfinder strongly limit this warmer and wetter period to the Noachian, pre-3.7 Ga and a dry and desiccating climate since.

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