Mars hosts a variety of interesting topography, such as the largest volcano and the biggest canyon in the solar system, as well as rippling sand dunes that constantly shift beneath the planet’s thin but windy atmosphere.
Studying how dunes ebb and flow over time can inform scientists about wind, climate, erosion, and sediment availability on the planet’s surface. But measuring dunes from space requires multiple images of the same spot, which is not easy to accomplish. NASA’s Mars Reconnaissance Orbiter (MRO) tracks how dunes migrate using its High Resolution Imaging Science Experiment (HiRISE) camera. Although the images HiRISE has sent back are gorgeous and boast submeter-scale resolutions, their clarity comes at a cost: The camera has limited coverage of the planet. Complementing HiRISE, the Context Camera (CTX), also aboard MRO, provides a more zoomed-out look at the Red Planet, allowing researchers to observe whole dune systems, which are typically tens of kilometers in scale, at once.
In a new study, Davis et al. combined images from HiRISE and CTX to study six geographic areas on Mars, each with unique weather and sand dunes, and to understand the limitations and errors that result from using the lower-resolution camera to study dunes. The researchers selected areas featuring active sand dune migration and good historical coverage by the orbiters; the areas selected also had to have been observed by both HiRISE and CTX during the same time period, but with enough time elapsed for differences among dunes to be detectable in meter-scale CTX images. Eventually, the team identified and measured changes in a total of 239 dunes across the six sites, with the images spanning 9 years.
Comparing portions of CTX images with their HiRISE counterparts revealed interesting findings. For the most part, CTX accurately captured dune migration rates, but dune heights tended to be underestimated, measuring, on average, only 67% as tall as the same dunes measured using HiRISE imagery.
The researchers say that overall, the findings suggest that CTX imagery can be used to analyze dunes in a much larger area of the Martian surface, which could, in turn, improve our understanding of how winds influence other dynamics on the planet. (Earth and Space Science, https://doi.org/10.1029/2019EA000874, 2020)
—David Shultz, Science Writer