Hacking a Mars rover’s tools has unearthed new insights into the planet

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Rocks on Mars are more porous and less compacted than scientists expected, according to a study that used data from NASA's Curiosity rover.

"This study represents the first gravity traverse and measurement of rock density on Mars". Image credit: NASA / JPL-Caltech / MSSS. In turn, this let the team calculate the density of the rock.

This set of accelerometers, called rover inertial measurement units, was recalibrated. In addition to the overall pull of Mars' gravity, higher density rocks in the subsurface exert a slightly greater downward gravitational force than lower density rocks. This novel strategy allowed the researchers to figure out how the huge Martian mountain whose base Curiosity is exploring formed-namely, that it was probably built up as a free-standing mound by the deposition of windblown sand and sediment. But because the satellites are so far away from their targets, the spatial resolution is limited.

Navigating the Martian surface can be risky (just look at the damage done to Curiosity's wheels!) but the rover's accelerometers and gyroscopes make the journey a little easier. Using the fact that gravitational fields weaken as altitude and distance from a planet's core increase, Lewis and team mapped out the gravitational field strength at more than 700 points from where Curiosity landed on the crater's floor up to where it had traveled into Mount Sharp's foothills.

"Curiosity, essentially, has a new science instrument six and a half years into its mission", Dr. Lewis said.

"This allows us to get new information about the subsurface of Mars in ways the rover was never created to do".

That enabled them to measure the subtle tug from rock layers on lower Mount Sharp, which rises 3 miles (5 kilometers) from the base of Gale Crater and which Curiosity has been climbing since 2014.

First, the researchers took into account Mars' rotation to accommodate expected changes in acceleration.

"Working from the rocks' mineral abundances as determined by Curiosity's Chemistry and Mineralogy instrument, we estimated a grain density of 2,810 kg/m".

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Next, they calibrated this raw information, accounting for the effects of temperature, the tilt of the rover, and other factors.

However, the team now says that their findings suggest the mountain wasn't buried as much as they had thought. "However, the bulk density that came out of our study is a lot less - 1,680 kilograms per cubic metre".

Mount Sharp is even more confounding to researchers than the crater because its peak is taller than the rim of the crater.

NASA considered dozens of landing sites for Curiosity but eventually settled on Gale Crater in part because it provided access to Mount Sharp.

The NASA image at the top of the page shows the region around Gale Crater, which Mars Science Laboratory's Curiosity rover is now exploring.

If these deposits had once been buried under 3 miles (5 km) of other sediments, they would nearly certainly be much denser, he added.

And this probably won't be the last time we hear about Curiosity "new" gravity instrument.

"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 at NASA's Jet Propulsion Laboratory in Pasadena, California, which manages the mission.

If Gale Crater had ever been filled to the brim, those pores in the rocks would have been essentially "squished out", as Lewis put it, beneath tons of rock. But Mount Sharp's upper layers appear to be easily eroded and more likely to be made of sediment than rock. "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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