Erosion rates on Mars and implications for climate change: Constraints from the Pathfinder landing site

The observation that the Mars Pathfinder landing site looks very similar to its appearance after it was deposited by catastrophic floods around 1.8-3.5 Ga allows quantitative constraints to be placed on the rate of change of the site since that time. The abundance of erosional features such as an exhumed former soil horizon, sculpted wind tails, ripplelike and other lag deposits, and ventifacts (fluted and grooved rocks) all suggest the site has undergone net deflation or loss of 3-7 cm of material. The presence of barchan dunes and ventifacts argues for erosion by saltating crystalline sand-size particles entrained in the wind. Most ventifacts probably formed soon after the catastrophic flood, which likely introduced a large, fresh supply of sand-size particles distributed across the rocky plain. The strongest winds blew toward the northwest during this time, resulting in the sculpting of ventifacts, deflation of the surface, collections of dunes within Big Crater and other lows, and possibly preferentially eroding small crater rims. The predominant wind direction changed to blow toward the southwest, similar to today. These winds further deflated the surface, completed the deposition of sand-size material in dunes and ultimately trapped these dunes in lows. The erosional features observed by Pathfinder indicate extremely low long-term deflation rates of 0.01-0.04 nm/yr since the end of the Hesperian (1.8-3.5 Ga) similar to less precise rates of <1 nm/yr based on the preservation of craters at the Viking 1 and Pathfinder landing sites. Short-term redistribution rates (deposition and removal) of atmospheric dust at the Pathfinder landing site and preexisting dust and sand at other locations on Mars are up to 10⁵nm/yr. Estimates of erosion rates on Mars show a rapid decrease by 3-6 orders of magnitude from 10²-10⁴nm/yr in Noachian terrains (characterized by rimless, flat-floored craters and valley networks) to the exceedingly slow rates (10^-2-10^-1nm/yr) operating during the Hesperian and Amazonian. Noachian erosion rates comparable to low continental denudation rates on Earth are consistent with erosion by running water and perhaps a more clement climate. The rapid decrease in erosion rates is consistent with a major climatic change during the Noachian, at the tail end of heavy bombardment, and a cold, dry, desiccating climate similar to today's since that time.