Small crater modification on Meridiani Planum and implications for erosion rates and climate change on Mars
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^(−6) 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.
Additional Information© 2014 American Geophysical Union. Received 29 APR 2014; Accepted 4 NOV 2014; Accepted article online 10 NOV 2014; Published online 10 DEC 2014. Research described in this paper was carried out by the Mars Exploration Rover Project, Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. All data from the Opportunity rover and HiRISE are available from the NASA Planetary Data System. N. Warner was supported by the NASA Postdoctoral Program. M. Lamb was supported by NASA grant NNX13AM83G. V. Ganti was supported by NSF NCED2 program. We thank Brad Jolliff for help with the crater catalog, John Grant for data on Eagle, Endurance, Victoria, and Santa Maria craters, Jane Willenbring for discussions on timescale bias in erosion rates, C. Fassett, T. Platz, R. Anderson, and P. Geissler for reviews, and V. Carranza, C. Schwartz, and E. Bondi for help with the figures.
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