Curiosity's first attempt at gravimetry advances martian geology

January 31, 2019

By cleverly repurposing a device onboard Curiosity normally used to detect the rover's movements on Mars to measure slight variations in gravitational fields instead, researchers have refined the understanding of how Gale crater and the mountain at its center formed. The gravitational field sensed by the rover as it traversed across the Martian crater's dusty basin indicates that the underlying sedimentary material is relatively porous, disproving a theory that the crater floor was once buried beneath several kilometers of rock. Since making planetfall in 2012, the Curiosity rover has been exploring the complex landscapes within Gale crater, a dry ancient lakebed. The rover has also been exploring the area surrounding Aeolis Mons (Mount Sharp), the 5-kilometer-tall mountain that forms a central peak in Gale crater. The origin of Mount Sharp is hotly debated; since the peak's summit is higher than much of the crater's rim, some researchers have suggested that the crater was once filled with sediment and the current topography is a result of erosion. Others have argued that wind-blown sediments collected at the crater's center, slowly building the Mount Sharp to its current altitude. Gravimetry, the precise measurement of tiny variations in gravitational fields, can be used to weigh mountains by detecting the density of subsurface materials. Orbital gravimetric surveys have been used to probe extra-terrestrial geology, but they lack the detail of the ground-based measurements available on Earth. However, when Curiosity left for Mars, it left its gravitational acceleration measuring tools behind. Kevin Lewis and colleagues devised a way to recalibrate the rover inertial measurement units (RIMUs), a set of accelerometers used for routine navigation, to measure local changes to the gravitational field. The clever use of Curiosity's RIMU as it traversed the crater and lower slopes of Mount Sharp revealed low-density porous rocks beneath the rover. Because deep burial would have compacted the rocks to a higher density, this indicates that only a fraction of the crater was ever filled in the past, the authors say. This adds support to the model that proposes Mount Sharp formed largely in its current form, as a free-standing mound within Gale.
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American Association for the Advancement of Science

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