Constraints on ripple migration at Meridiani Planum from Opportunity and HiRISE observations of fresh craters

Abstract

[1] Observations of fresh impact craters by the Opportunity rover and in high-resolution orbital images constrain the latest phase of granule ripple migration at Meridiani Planum to have occurred between ∼50 ka and ∼200 ka. Opportunity explored the fresh Resolution crater cluster and Concepción crater that are superposed on and thus younger than the ripples. These fresh craters have small dark pebbles scattered across their surfaces, which are most likely fragments of the impactor, suggesting that the dark pebbles and cobbles observed by Opportunity at Meridiani Planum are a lag of impactor-derived material (either meteoritic or secondary impactors from elsewhere on Mars). Two larger, freshrayed craters in Meridiani Planum bracket ripple migration; secondaries from Ada crater are clearly superposed on and secondaries from an unnamed 0.84 km diameter crater have been modified and overprinted by the ripples. Three methods were used to estimate the age of these craters and thus when the latest phase of ripple migration occurred. The inactivity of the ripples over the past ∼50 ka at Meridiani is also consistent with other evidence for the stability of the ripples, the lack of observed eolian bed forms in craters that formed in the past 20 years, and little evidence for much dune motion in the past 30 yr on Mars. Observations of crater morphology and their interaction with the ripples allow the development of a general time scale for craters in Meridiani Planum over the past million years.

Bedform migration on Mars: Current results and future plans

“…Global studies show that bright TARs are generally older than dark dunes and lack any clear evidence of recent activity (Balme et al, 2008;Bridges et al, 2012a). This seems confirmed by evidence of cratered and eroded TARs reported from several areas of Mars (Reiss et al, 2004;Golombek et al, 2010;Kerber and Head, 2011). Analyses of HiRISE data show that TARs with heights P1 m with symmetrical topographic profiles are most similar to reversing dunes, whereas TARs with heights 60.5 m have profiles more like granule ripples (Zimbelman, 2010).…”

Source-to-Sink

“…Most notably, Silvestro et al (2010b) report ;1.7 m of migration within 4 months for ripples on the stoss slope of a barchan dune in Nili Patera. In contrast, Golombek et al (2010) show that no migration has occurred in hundreds of thousands of years for a field of ripples at Meridiani Planum, and calculated dune migration rates under present conditions are orders of magnitude slower than on Earth Andreotti 2006, Parteli andHerrmann 2007). Currently, an understanding of the frequency of sand transport on Mars is hindered by both the limited time-series of dune images needed to determine morphological change and the unknown ages of eolian features globally.…”

Recent developments in planetary Aeolian studies and their terrestrial analogs

“…Extrapolation of the rate of movement of granule-coated megaripples on Earth to (Viking-like) Martian conditions indicated that a 25-cm-high megaripple on Mars could take from hundreds to thousands of Earth years to move only 1 cm (Zimbelman et al, 2009). Observations both from orbit and from the Opportunity rover indicate that the megaripples on Meridiani Planum likely had their latest phase of granule ripple migration between $50 and $200 ka, as evidenced by crater ejecta deposits from two fresh-rayed craters that are superposed on, or superposed by, the granule-coated megaripples (Golombek et al, 2010). The stability of megaripples contrasts with sand ripple migration observed on many Martian sand dunes (Section 6.3), but is broadly consistent with recent evidence that some TARs exposed within the eroded Medusae Fossae Formation (discussed in the following section) are substantially cratered (Kerber and Head, 2011); cratered Aeolian features (Fig.…”