NASA’s Curiosity rover has made an unexpected discovery while trekking the slopes of Mount Sharp — a 3.4-mile-high mountain rising in the middle of Gale Crater on Mars. For the first time ever, the six-wheeled robot has managed to measure the gravity of the Martian ground and to reveal the density of this imposing mountain, NASA announced in a news release.

The intrepid Mars explorer has been climbing up the mountain ever since it first landed on the red planet in August of 2012. Armed with extremely sensitive instruments, which include accelerometers and gyroscopes, the rover has been taking precise measurements of its surroundings all throughout its six-year hike up Mount Sharp.

Now, in a serendipitous twist of events, a team of NASA collaborators led by Johns Hopkins University has figured out how to use those instruments to measure Mars’ gravity. In a paper published today in the journal Science, the team explained how they re-purposed Curiosity’s sensors and turned them into gravimeters to measure the gravitational pull of the ground which the robot had been roving on.

“Curiosity, essentially, has a new science instrument six and a half years into its mission,” said study lead author Kevin Lewis, an assistant professor in Johns Hopkins University’s Earth and Planetary Sciences department.

“This allows us to get new information about the subsurface of Mars in ways the rover was never designed to do.”

Vroom! ????️ Whether you’re on a Moon buggy or a Martian rover (or whether you’re using a gravimeter or an accelerometer) you can measure gravitational changes. These findings are helping us learn how the Martian landscape was formed! Strap in: https://t.co/WJxyZSGU3D pic.twitter.com/qhnpqDjFt6 — NASA (@NASA) February 1, 2019

First Surface Gravity Measurements On An Alien Planet

As NASA explained, Curiosity’s accelerometers can be used as gravimeters to detect the planet’s gravity whenever the rover is standing still. By analyzing data gathered during the first five years of the Mars mission — which encompassed more than 700 accelerometer measurements taken between October 2012 and June 2017 — the scientists were able to calculate Mars’ gravitational acceleration.

According to Science Alert, Lewis’ team extracted the acceleration due to planetary rotation and corrected for factors such as tilt, elevation, and temperature. This led to precise measurements of gravitational acceleration and of surface gravity.

While astronomers have previously measured the surface gravity of the moon during the Apollo 17 mission in 1972, this is the first time that scientists have taken surface gravity measurements on an alien planet, notes Johns Hopkins University.

Unexpected Discovery About Mount Sharp

Knowing the surface gravity on Mars enabled the team to find out another thing that had previously remained a mystery — the density of the Martian rock. Data gathered by Curiosity during its trek across the Gale Crater and up the lower slopes of Mount Sharp revealed that the mountain’s lower layers are much less dense than expected.

The Gale Crater on Mars, with Mount Sharp at its center and with Curiosity’s landing site circled in yellow. Featured image credit: NASA/JPL-Caltech/ASU/UA

“The lower levels of Mount Sharp are surprisingly porous,” said Lewis.

To estimate the bulk density of the material inside Gale Crater, the team looked at data on rock mineral abundance collected by Curiosity’s Chemistry and Mineralogy instrument. Their original estimates pointed to a grain density of about 2,810 kilograms per cubic meter, said study co-author Travis Gabriel, a geologist and graduate student in Arizona State University’s School of Earth and Space Exploration.

“However, the bulk density that came out of our study is a lot less — 1,680 kilograms per cubic meter.”

Until now, scientists had largely believed that Mount Sharp was carved out of sediment that once filled the entire Gale Crater. But these latest findings challenge that assumption, suggesting that the mountain may have formed in a different way.

“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,” said Lewis.

The lower layers of Mount Sharp at the base of the Martian mountain. Featured image credit: NASA/JPL-Caltech/MSSS Wikimedia Commons/Resized

Judging by the low density of the mountain’s lower layers, it is possible that Gale Crater was only partly filled with sediment. The study uncovered that the lower layers of Mount Sharp have been compacted by only a half-mile to a mile — much less than if the crater had been full to the brim, with all that extra sediment weight pressing down on the base of the mountain.

This, in turn, suggests that the upper layers of Mount Sharp were built up by wind and blowing sand rather than by eroded sediment displaced from the crater floor.

“There are still many questions about how Mount Sharp developed, but this paper adds an important piece to the puzzle,” said study co-author Ashwin Vasavada, Curiosity’s project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California.