Rover measures Mars gravity

Marsrover makes first gravity measurement on a foreign planet

Marsrover Curiosity has performed the first gravity measurement on the surface of an alien planet. © NASA / JPL-Caltech / MSSS
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A rover as a gravimeter: The Mars rover Curiosity has carried out the first gravity measurements on an alien planet - and so "shining through" the underground. NASA researchers have misused the data from the acceleration sensors of the Mars vehicle. The surprising result: The underground in the Gale crater is much more porous than thought, as the scientists report in the journal "Science".

The Curiosity Mars rover is a veteran pioneer: Since August 2012, the rolling chemistry lab has been exploring the Gale Crater and the landscape around Mount Sharp - and has already made some exciting discoveries. Thus, Curiosity has detected organic molecules in the Martian underground and found possible evidence of a continental Martian crust. In addition, his analyzes provided evidence that there was once a life-friendly freshwater lake in the Gale Crater.

Inertia sensors converted to gravity knives

Now the Mars rover has once again done a pioneering feat: for the first time he has performed a gravity measurement on the surface of Mars - the first on a foreign planet. To get this data, the researchers around Kevin Lewis from Johns Hopkins University had to be creative: "Curiosity has among his instruments none that can measure changes in gravity, " the researchers explain.

But the Rover has several inertial gauges, which he uses for position determination and navigation while driving. Similar to the acceleration sensors in a smartphone, they register changes in speed and position. However, when the Mars rover is stationary, Mars' gravity acts on these sensors. It's precisely this data that Lewis and his team have used to derive gravity field measurements through recalibration and analysis.

First gravity traverse on a foreign planet

From 700 readings over the past five years, the researchers reconstructed a gravity profile of the lower slopes of Mount Sharp - the terrain that Curiosity explored at that time. "This represents the first gravity traverse and measurement of rock density on Mars, " says co-author Nicholas Schmerr of the University of Maryland. Never before has such a measurement been done on the surface of an alien planet. display

"This allows us to get completely new information about the rock beneath the surface of Mars, " says Lewis. Although some orbital probes have already measured the gravitational field of the red planet. However, because they are so far from the surface, their resolution is low. The entire Gale Crater with its 150 kilometers in diameter is little more than a splash of color in these maps. The Curiosity measurement data, however, allow an almost meter-accurate resolution.

The readings show a decrease in gravity with increasing slope height at Mount Sharp. Lewis Kevin Lewis

Crater rock is surprisingly porous

The surprising result: "The density of the sedimentary rock is 1, 680 kilograms per cubic meter, " the researchers report. "That's much less than expected." Previously, density measurements of individual mineral samples had almost doubled 2, 810 kilograms per cubic meter. The scientists conclude that the dense minerals in the rock are interspersed with many cavities. "The lower slopes of Mount Sharp are therefore surprisingly porous, " says Lewis.

This sheds new light on the genesis of this Martian crater mountain. Previously it was believed that the crater was once filled completely with sediment. Only the erosion then released the approximately three kilometers high mountain again. But the new data contradicts this scenario. "The low density in the rocks of the Gale crater suggests that they were never deeply buried, " says Schmerr. "Instead, Mount Sharp could have been created by wind deposition and similar processes."

Useful for other missions

According to the scientists, these results demonstrate how valuable gravimetric experiments can be with the help of mobile probes. Rover measurements can supplement gravity data from orbit - and bring surprising insights. (Science, 2019; doi: 10.1126 / science.aat0738)

Source: University of Maryland

- Nadja Podbregar