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'Mars Buggy' Curiosity Measures a Mountain's Gravity

Apollo 17 astronauts drove a moon buggy across the lunar
surface in 1972, measuring gravity with a special instrument. There are no
Astronauts on Mars, but a group of clever researchers realized that they were the tools for similar experiments with the
Martian buggy they're operating.

In a new paper in science, the researchers detail how they
repurposed sensors used to drive the Curiosity rover and turned them into
gravimeters, which measure changes in gravitational pull. That enabled them to measure
the subtle tug from rock layers on the lower Mount Sharp, which rises 3
miles (5 kilometers)
from the base of Gale Crater and Which Curiosity
has been climbing since 2014. The results? It turns out the density of those
rock layers is too low than expected.

Just like a smartphone, Curiosity carries accelerometers
and gyroscopes. Moving your smartphone allows these sensors to determine its
location and which way it's facing. Curiosity's sensors do the same thing but with
far more precision, playing a crucial role in navigating the Martian surface on
each drive. Knowing the rover's orientation also lets engineers accurately
point its instruments and multidirectional, high-gain antenna.

By happy coincidence, the rover's accelerometers can be
used as Apollo 17's gravimeter. The accelerometers detect the gravity of the
planet whenever the rover stands still. Using engineering data from the first
five years of the mission, the paper's authors measured the gravitational tug
of Mars on the rover. As Curiosity ascends Mount Sharp, the mountain adds additional
Gravity – but not as much 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 were not buried by as
much material as we thought. "

Science from a Mars

The Apollo 17 astronauts drove their buggy across the
Moon's Taurus-Littrow Valley, periodically stopping to capture 25 measurements.
Lewis has studied Martian gravity fields using data collected by NASA's orbiters
and was familiar with Apollo 17's gravimeter.

The Science paper uses over 700 measurements from
Curiosity's accelerometers, taken between October 2012 and June 2017. These
data were calibrated to filter out "noise," such as the effects of
temperature and the tilt of the rover during its climb. The calculations were then
'to gravity fields to ensure accuracy.

The results were also compared to mineral-density
estimates from Curiosity's Chemistry and Mineralogy instrument, which characterizes
the crystalline minerals in rock samples by using an X-ray beam. That data
helped inform how the porous the rocks are.

Mountain of Mystery

There are many mountains within craters or canyons on
Mars, but some approach to scale of Mount Sharp. Scientists still are not sure
how the mountain grew inside the Gale Crater. One thought is that the crater was
once filled with sediment. How much of it was filled remains a source of
debate, but the thinking is that many millions of years of wind and erosion
eventually excavated the mountain.

If the crater had been filled to the brim, all that
material must have pressed down, or compacted, the many layers of
fine-grained sediment beneath it. But the new paper suggests Mount Sharp's
Lower layers have been compacted by only a half-mile to a mile (1 to 2
km) – much less than if the crater was full.

"There are still many questions about Mount 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. JPL manages the Mars Science
Laboratory mission that Curiosity is a part of. "I'm thrilled that
creative scientists and engineers are still finding innovative ways to make new
scientific discoveries with the rover, "he added.

Lewis said that Mars holds plenty of mystery beyond Mount
Sharp. Its landscape is like Earth's, but sculpted more by wind and blowing
sand than by water. They are planetary siblings, at once familiar and starkly

"To me, Mars is the uncanny valley of Earth,"
Lewis said. "It's similar but was shaped by different processes
so unnatural to our terrestrial experience. "

For more
About Curiosity, visit:

For more
About NASA's Mars program, visit:

News Media Contact

Andrew Good
Jet Propulsion Laboratory, Pasadena, Calif.


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