Small crater modification on Meridiani Planum and implications for erosion rates and climate change on Mars

Abstract

A morphometric and morphologic catalog of~100 small craters imaged by the Opportunity rover over the 33.5 km traverse between Eagle and Endeavour craters on Meridiani Planum shows craters in six stages of degradation that range from fresh and blocky to eroded and shallow depressions ringed by planed off rim blocks. The age of each morphologic class from <50-200 ka to~20 Ma has been determined from the size-frequency distribution of craters in the catalog, the retention age of small craters on Meridiani Planum, and the age of the latest phase of ripple migration. The rate of degradation of the craters has been determined from crater depth, rim height, and ejecta removal over the class age. These rates show a rapid decrease from~1 m/Myr for craters <1 Ma to~<0.1 m/Myr for craters 10-20 Ma, which can be explained by topographic diffusion with modeled diffusivities of~10 À6 m 2 /yr. In contrast to these relatively fast, short-term erosion rates, previously estimated average erosion rates on Mars over~100 Myr and 3 Gyr timescales from the Amazonian and Hesperian are of order <0.01 m/Myr, which is 3-4 orders of magnitude slower than typical terrestrial rates. Erosion rates during the Middle-Late Noachian averaged over~250 Myr, and~700 Myr intervals are around 1 m/Myr, comparable to slow terrestrial erosion rates calculated over similar timescales. This argues for a wet climate before~3 Ga in which liquid water was the erosional agent, followed by a dry environment dominated by slow eolian erosion.

Selection of the InSight Landing Site

“…Using the topographic data coupled with the crater model ages, we estimate a crater degradation rate of 0.02-0.03 m/Myr for 200-m-sized craters, similar to other Hesperian to Amazonian erosion rates on Mars (Golombek et al 2014c). Assuming similar degradation rates for 100 to 200 m size craters and using standard d/D of 0.2 for fresh, simple primary craters of this size (Wood and Andersson 1978;Pike 1980; Tornabene et al 2013), it is feasible that some <200-m-sized craters were completely planed off or buried over 500 to 700 Myr.…”

“…Roughly 44 SHARAD observations in the InSight landing site area have been analyzed and no evidence for subsurface water or ice from dielectric properties or subsurface reflectors has been found. Finally, analysis of the rate of degradation of rocky ejecta craters indicate erosion rates ) consistent with slow eolian erosion rates at other landing sites and far too slow for erosion associated with liquid water (Golombek et al 2014c).…”

“…In the absence of surface processes that erode or bury craters and rocks, all craters that are large enough to have accessed the rocky layer should have rocks in their ejecta blanket. This is particularly true for fresh craters that are too young to have been obliterated by modern degradational processes that operate at extremely low rates (e.g., 2014c). The SFD of these larger, fresh rocky craters should follow a crater production function (Ivanov 2001).…”

Amazonian chemical weathering rate derived from stony meteorite finds at Meridiani Planum on Mars

“…Furthermore, Endurance has experienced considerably less total erosion than Victoria2021 and is therefore younger given their proximity and similarity in target materials. Moreover, Barberton is not on a pedestal like the iron meteorite Block Island10 and adjacent surfaces are not significantly scoured as might be expected given the ease with which surrounding rocks are eroded1720. Nevertheless, these two hypotheses constrain other intermediate possibilities (that is, the meteorites fell after some of the Meridiani terrains formed), and we will consider both hypotheses to constrain the maximum and minimum meteorite exposure age on the surface.…”

“…The four meteorites are found on a diversity of terrains that make up the area traversed by the Opportunity rover17. Santa Catarina and similar cobbles718 appear strewn across the smooth, sandy annulus around the Victoria impact crater (Fig.…”