Martian aeolian activity at the Bagnold Dunes, Gale Crater: The view from the surface and orbit

Abstract

The first in situ investigation of an active dune field on another planetary surface occurred in 2015–2016 when the Mars Science Laboratory Curiosity rover investigated the Bagnold Dunes on Mars. High Resolution Imaging Science Experiment images show clear seasonal variations that are in good agreement with atmospheric model predictions of intra‐annual sand flux and migration directions that together indicate that the campaign occurred during a period of low wind activity. Curiosity surface images show that limited changes nevertheless occurred, with movement of large grains, particularly on freshly exposed surfaces, two occurrences of secondary grain flow on the slip face of Namib Dune, and a slump on a freshly exposed surface of a large ripple. These changes are seen at Martian solar day (sol)‐to‐sol time scales. Grains on a rippled sand deposit and unconsolidated dump piles show limited movement of large grains over a few hours during which mean friction speeds are estimated at 0.3–0.4 m s−1. Overall, the correlation between changes and peak Rover Environmental Monitoring Station (REMS) winds is moderate, with high wind events associated with changes in some cases, but not in others, suggesting that other factors are also at work. The distribution of REMS 1 Hz wind speeds shows a significant tail up to the current 20 m s−1 calibration limit, indicating that even higher speed winds occur. Nonaeolian triggering mechanisms are also possible. The low activity period at the dunes documented by Curiosity provides clues to processes that dominated in the Martian past under conditions of lower obliquity.

Sedimentary processes of the Bagnold Dunes: Implications for the eolian rock record of Mars

“…Some degree of grain sorting by the avalanche process is inferred by color differences between the flow edges and their interiors with the expectation that relatively coarser grains are more abundant in the toes than elsewhere (Figures a and b) [ Allen , ]. Where the rover scuffed the large ripple and triggered grainflows, this type of sorting was visible as coarse, white grains, interpreted to be calcium sulfate deflated from the interdune bedrock, preferentially concentrate at the edges of the flows (Figure a) [ Bridges et al ., ; Elhmann et al ., ].…”

Compositional variations in sands of the Bagnold Dunes, Gale crater, Mars, from visible‐shortwave infrared spectroscopy and comparison with ground truth from the Curiosity rover

“…Untangling the effects of mineral abundances, grain sizes, and dust cover from orbit remains difficult, and ground truth is required to definitively exclude the possibility that compositional variations merely indicate differences in masking of the primary mineralogy by dust. The Bagnold Dunes were previously determined to be generally dust‐free [ Rogers and Bandfield , ], are relatively active near the rover traverse (e.g., Figure c) [ Silvestro et al , , ; Bridges et al , ; Ewing et al , ] with dune displacements of about half those measured in the very active Nili Patera dune field [ Bridges et al , ], and HiRISE red/infrared band ratios are relatively high over the dunes (Figure b). In the following section, we quantitatively constrain the modal composition of bulk sands at four locations, assuming that the Bagnold sands are relatively dust‐free (an assumption later discussed in section 4.2).…”

Aeolian saltation on Mars at low wind speeds

“…However, a band of dark, mafic sand dunes, designated (unofficially) as the Bagnold dunes, extends across most pathways between Curiosity's touch‐down point on the north part of the crater floor and the mission's main exploration objective on the lower flanks of the central mountain. The Bagnold dunes, which are part of a larger system of sand that covers much of the western, southern, and eastern crater floor [ Day and Kocurek , ], are known to be currently active from subtle morphological changes observed from orbit [ Silvestro et al ., , ; Bridges et al ., ].…”