Curiosity’s First Gravity Measurement Reveals What Lies Beneath Gale Crater On Mars

This May 11, 2016, self-portrait of NASA's Curiosity Mars rover shows the vehicle at the 'Okoruso' drilling site on lower Mount Sharp's 'Naukluft Plateau.' NASA/JPL-Caltech/MSSS 

NASA’s Curiosity rover has been a great explorer of Mars, contributing to new discoveries and expanding our understanding of the Red Planet. Now, it will also be responsible for a discovery that it was not designed for. It measured the gravity underneath its wheels and discovered what it’s like beneath Gale Crater.

The gravimetric measurements were achieved by the research team using instruments that can track the movement of the rover. This clever repurposing of non-scientific engineering data allowed them to work out that the rocks underneath Gale Crater are quite porous and not as hard as previously thought. The findings are reported in Science.

“What we were able to do is measure the bulk density of the material in Gale Crater,” co-author Travis Gabriel, a graduate student at Arizona State University, said in a statement. “Working from the rocks’ mineral abundances as determined by the Chemistry and Mineralogy instrument, we estimated a grain density of 2,810 kilograms per cubic meter. However, the bulk density that came out of our study is a lot less – 1,680 kilograms per cubic meter.”

Curiosity landed on Mars in 2012 and since then it has explored Gale Crater, which is most likely an ancient lake. In 2014 the rover began climbing the main feature of the crater, Mount Sharp, and researchers expected to see the density of the rocks increasing as Curiosity climbed further up the 5,500-meter-high (18,000-foot) mountain. But that was not the case.

“The lower levels of Mount Sharp are surprisingly porous,” explained lead author Kevin Lewis of Johns Hopkins University. “We know the bottom layers of the mountain were buried over time. That compacts them, making them denser. But this finding suggests they weren’t buried by as much material as we thought.”

This study was possible thanks to the use of the accelerometers inside Curiosity. Just like the ones in your phone that can tell the software how you’re moving your device, the one in Curiosity tells the mission team what the rover is doing. Turning the data on its head, 700 points were used to track subtle gravitational changes. Currently, it appears that Mount Sharp's lower layers are only compressed by less than 2 kilometers (about a mile) of material. Considerably less than if the crater had been full.

“There are still many questions about how Mount Sharp developed, but this paper adds an important piece to the puzzle,” added Ashwin Vasavada, Curiosity’s project scientist at NASA’s Jet Propulsion Laboratory. “I’m thrilled that creative scientists and engineers are still finding innovative ways to make new scientific discoveries with the rover.”

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