Gusev crater: Wind‐related features and processes observed by the Mars Exploration Rover Spirit

Abstract

[1] Wind-related features observed by the rover Spirit in Gusev crater, Mars, include patches of soil on the surface, some of which are organized into bed forms. Windblown grains include dust (inferred to be <3 mm in diameter), sands (up to a few hundred mm in diameter), and granules (>2 mm in diameter). Microscopic Imager data show the sands and granules to be rounded and relatively spherical, typical of grains transported long distances by the wind. The interior of bed forms exposed by rover operations suggests the infiltration of dust among the grains, indicating that these sands are not currently experiencing saltation. Orientations of 1520 features (such as bed forms and ventifacts) along Spirit's traverse from the landing site (the Columbia Memorial Station) to West Spur in the Columbia Hills suggest primary formative winds from the north-northwest, which correlate with measurements of features seen in orbiter images and is consistent with afternoon winds predicted by atmospheric models. A secondary wind from the southeast is also suggested, which correlates with predictions for nighttime/early morning winds. Wind abrasion is indicated by ventifacts in the form of facets and grooves cut into rocks, the orientations of which also indicate prevailing winds from the north-northwest. Orientations of many aeolian features in the West Spur area, however, have more scatter than elsewhere along the traverse, which is attributed to the influence of local topography on the patterns of wind. Active dust devils observed on the floor of Gusev from the Columbia Hills demonstrate that dust is currently mobile. Sequential images of some dust devils show movement as rapid as 3.8 m/s, consistent with wind velocities predicted by atmospheric models for the afternoon, when most of the dust devils were observed. Sands accumulated on the rover deck in the same period suggest that some sands in the Columbia Hills experience active saltation. ''Two-toned'' rocks having a light band coating at their bases are considered to represent partial burial by soils and subsequent exposure, while ''perched'' rocks could represent materials lowered onto other rocks by deflation of supporting soils. Measurements of the heights of the light bands and the perched rocks range from <1 cm to 27 cm, indicating local deflation by as much as 27 cm.

Mars Exploration Rover Pancam multispectral imaging of rocks, soils, and dust at Gusev crater and Meridiani Planum

“…Vortexes in the atmosphere are capable of lifting dust, which is typically "bright," into the atmosphere, leaving coarser grained materials on the surface, which then appear comparatively dark. Spirit MI images show that soils within such a "dark" streak are relatively free of dust, whereas Mi images outside the streak appear dustier, confirming this model (Greeley et al, 2005(Greeley et al, , 2006a.…”

Source-to-Sink

“…Thermal inertia data from space-borne imagery of Mars indicates that Martian dunes have an average grain size that is coarser (medium-to coarsegrained sand) than on Earth Christensen 1991, Presley andChristensen 1997). Limited surface observations (e.g., Gusev Crater by Greeley et al [2006] and Sullivan et al [2008]; Meridiani Planum by Jerolmack et al [2006]) indicate eolian sands that are similar in size or slightly finer than those on Earth.…”

Transverse Aeolian Ridges (TARs) on Mars

“…The Mars Exploration Rover Opportunity found that the regolith in the Meridiani region was a poorly sorted mix of fine basaltic sand and hematite granule-sized concretion fragments (Sullivan et al, 2005), and the Spirit rover also observed granule-coated ripples where the granules were comprised of rounded rock fragments (Greeley et al, , 2006. Where the regolith was worked into ripples, a monolayer of fragments was often seen on the ripple crests, with basaltic sands on the flanks, and whole concretions or other clasts mixed with basaltic sands in the inter-ripple zones.…”