How did this mountain form on Mars? The Curiosity rover investigates

NASA's Curiosity rover in 2015 (Photo by NASA/JPL-Caltech/MSSS via Getty Images)

NASA’s Curiosity rover has been helping uncover the secrets of Mars since landing on the Red Planet in August 2012. It has drilled into rocks and soil and taken photos of odd features so that scientists can learn more about Mars and its history. Most important, it has explored Gale crater, a vast and dry ancient lake bed with a mountain at its center.

Now, a team of researchers has repurposed one of the rover’s instruments to help determine how Gale Crater and 16,404-feet-tall Mount Sharp formed. The findings are detailed in a study published Thursday in the journal Science.

This set of accelerometers, called rover inertial measurement units, was recalibrated. Accelerometers are also used in smartphones to help determine motion and orientation.

The device is meant to detect the rover’s movements on the Martian surface and assist with navigation, but the researchers were able to use it to measure variations in gravitational fields as the rover navigated the crater and Mount Sharp’s lower slopes.

As Curiosity roved the dusty basin of Gale Crater, the instrument sensed that the sediment underneath is porous. It had been believed that the floor of Gale Crater was once buried beneath miles of rock, but the porous finding disproves that.

“What we were able to do is measure the bulk density of the material in Gale Crater,” said Travis Gabriel, study co-author and graduate student at Arizona State University’s School of Earth and Space Exploration, in a statement.

Mount Sharp is even more confounding to researchers than the crater because its peak is taller than the rim of the crater. This led to the idea that the crater had been full of sediment and what we see today is the result of erosion. Another competing idea is that the sediments collected in the crater and helped form Mount Sharp.

There are other craters on Mars with central peaks, raised by the impact that formed the crater. But Mount Sharp’s upper layers appear to be easily eroded and more likely to be made of sediment than rock.

Researchers have ways of weighing mountains. By collecting the measurements of small variations in gravitational fields, or gravimetry, the density of the subsurface materials composing a mountain can be detected.

The porous rocks beneath the crater’s surface have a low density. If they were buried deeper and compacted, they would have a higher density. This helped the researchers determine that the crater was filled by only a fraction in the past.

“The lower levels of Mount Sharp are surprisingly porous,” Kevin Lewis, lead study author and assistant professor at Johns Hopkins University’s Department of Earth and Planetary Sciences, said in a statement. “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 adds more evidence to the idea that Mount Sharp formed as a freestanding mound in the crater.

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

Gabriel added, “This is a testament to the utility of having a diverse set of techniques with the Curiosity rover, and we’re excited to see what the upper layers of Mount Sharp have in store.”

Curiosity’s mission continues, and it’s on the move again. It took its last “selfie” on the twisting Vera Rubin Ridge, a feature between the crater wall and Mount Sharp the rover has been exploring since September 17. Now, Curiosity will study clay minerals that may have helped form the lower levels of Mount Sharp.

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