A mix of rock and sand greeted the Curiosity Rover as it approaches the Bagnold Dune field, the dunes slowly encroaching on weathered outcrops. This is our first visit to active dunes anywhere but on Earth.
Curiosity is currently taking photos as it inches closer and closer to the dark sands of the Bagnold Dunes. Once it reaches its target dune, it’ll use its scoop to collect a sample for analysis, and sideswipe the sand with a wheel to scuff a fresh surface to ogle the dune’s interior.
The position of the Curiosity Rover is marked on the satellite image below, near the center. Interestingly, none of the outcrops share the distinct dark colour that would indicate an easy source for freshly-eroding sediment.
Curiosity’s path is marked with a thin yellow line and tiny black datestamps. Image credit: NASA
The dark Bagnold Dunes are composed at least in part of olivine, a mineral common to dark volcanic rocks (basalt). Researchers are hoping Curiosity will be able to determine if the wind is sorting minerals, separating heavier olivine from other minerals.
The Bagnold Dunes are active: satellite images reveal them creeping about a meter (3 feet) per year. This is our first up-close look at Martian sand dunes, in contrast to sand ripples and drifts. Unlike ripples or drifts, dunes have enough sand that the windblow sediments can slide down the steep downwind face.
The texture of Martian dunes is different than here on Earth. Mission planner for the dune expedition Nathan Bridges explains:
“The ripples on them are much larger than ripples on top of dunes on Earth, and we don’t know why. We have models based on the lower air pressure. It takes a higher wind speed to get a particle moving. But now we’ll have the first opportunity to make detailed observations.”
A colourized version of the Bagnold Dunes assembled from multiple frames. Image processing may have over-darkened the dunes. Image credit: NASA/Paul Hammond
Interesting geological features in this area will be named for Nambian geological place names in a tribute to the Namib Desert that has offered such an excellent terrestrial analogue for interpreting Martian dunes and playas.