NASA's Mars Curiosity rover has successfully taken measurements of gravity on the red planet to study the density of different rock layers on a mountain.
On-board accelerometers and gyroscopes were used to measure the force of gravity as the rover ascended a mountain in the Gale Crater.
It turns out the density of those rock layers is much lower than expected.
The finding also provides a new technique for scientists to use in the future as the rover continues its trek across the 96-mile-wide crater and up Mount Sharp, a three-mile-high mountain in the middle of it.
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NASA's Curiosity rover has been scaling Mount Sharp, and three-mile-high mountain in the Gale Crater. It's instruments have detected that the mountain is less dense than originally thought, throwing up more questions about how it was formed
As Curiosity ascended Mount Sharp, the gravitational force increased — but not as much as scientists expected.
'The lower levels of Mount Sharp are surprisingly porous,' said 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.'
Researchers used more than 700 measurements taken between October 2012 and June 2017 to take the measurements.
These were calibrated to filter out 'noise', such as the effects of temperature and the tilt of the rover during its climb.
Calculations were then compared to models of Mars' gravity fields to ensure accuracy.
Scientists also also compared the findings to mineral-density estimates from Curiosity's Chemistry and Mineralogy instrument, which looks at the minerals in martian rock samples by using an X-ray beam.
That data helped inform how porous the rocks are.
'We estimated a grain density of 2810 kilograms per cubic meter,' said researcher, Travis Gabriel. 'However the bulk density that came out of our study is a lot less - 1680 kilograms per cubic meter.'
The lower figure shows that the rocks are likely to be more porous, meaning they have been compressed less than scientists had thought.
'The lower levels of Mount Sharp are surprisingly porous,' said 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 image shows a scene from the far left of the Gale Crater, when viewed from the top of the Vera Rubin Ridge
An image of Gale Crater's northern rim, around 1.2 miles above the rover. It shows a scene from around two fifths along the ridge
This image shows the view of the far right hand side of the crater, from Curiosity's perspective
NASA's Mars rover Curiosity captured this composite image, which looks toward the higher regions of Mount Sharp, in September, 2015
Scientists are still unsure about how Mount Sharp formed and Mars has several craters with central peaks raised by the shock of the impact that created them, but few are this large.
Impact from meteorites would account for some of the mound's height, but its upper layers appear to be made of