Curiosity measures Mount Sharp's gravity

Curiosity accidentally recreated an experiment first performed by Apollo 17, finding that Mount Sharp is not as dense as previously thought. The finding throws uncertainty on how the mountain was created.

Curiosity inadvertantly recreated an experiment that was first run by the Apollo 17 astronauts using the Lunar buggy.

Credit: NASA/JPL-Caltech

The Curiosity rover has been measuring the gravity of Mars for the last five years – echoing an experiment run by Apollo 17 – all without even realising it!

The measurements reveal the gravity profile of Mount Sharp, the 5km mountain that Curiosity is currently exploring, showing it has a much lower density than expected.

The find throws uncertainty over how the mountain was created.

Curiosity inadvertently measured the gravitational pull using its accelerometer, an instrument that usually measures the rover’s acceleration.

However, when the rover is stationary instead measures the planet’s gravity.

A similar experiment was run by the Apollo 17 astronauts as they explored the Moon, but they had a specialist instrument.

Instead, the Curiosity team had to search through the rover’s engineering data from October 2012 to June 2017.

During this time Curiosity was approaching and then climbing Mount Sharp, and so planetary geologists were able to create a gravitational profile of the many layers of rock that lie beneath the surface.

By comparing this profile with the readings of other instruments which studied the composition of crystalline minerals in the rock, they were able to measure the density of the rock hidden beneath the surface.

The results were unexpected.

“The lower levels of Mount Sharp are surprisingly porous,” says Kevin Lewis from Johns Hopkins University, who led the study.

Previously, geologists thought that the Gale Crater used to be filled with sediment, which has been excavated over time, leaving Mount Sharp behind.

However, if Gale Crater was filled to the brim, it would have put a lot of pressure on the lower layers of what would become Mount Sharp.

“That compacts them, making them denser. But this finding suggests that they weren’t buried by as much material as we thought,” says Lewis

“There are still many questions about how Mount Sharp developed,” says Ashwin Vasavada, Curiosity’s project scientists from JPL. “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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