Curiosity measures gravity of Mount Sharp
NASA’s Curiosity rover, which has now departed Mount Sharp’s Vera Rubin Ridge where it spent more than a year and rode out a months-long global Martian dust storm, has measured the gravity on Mount Sharp in much the same way Apollo 17 astronauts measured the Moon’s gravity in 1972.
To replicate the process used by the Apollo 17 astronauts, who used a special instrument aboard the Lunar Roving Vehicle they drove on the Moon’s surface, mission scientists adapted sensors used to drive Curiosity remotely into gravimeters, which track changes in an area’s gravitational pull.
By measuring the gravitational pull of rock layers on the lower part of the mountain, scientists found those layers to be much less dense than expected.
Using accelerometers, or instruments that measure changes in a vehicle’s acceleration, and gyroscopes, spinning disks that calculate angular velocity, which is the rate at which an object rotates around another object, a team of scientists led by Kevin Lewis of Johns Hopkins University essentially repeated the measurements Apollo 17’s gravimeters conducted along the Moon’s Taurus-Littrow Valley on the lower rock layers of the Red Planet’s Mount Sharp.
Like Apollo 17’s gravimeter, Curiosity’s accelerometers studied a region’s gravity every time the rover stopped moving. Scientists also incorporated engineering data taken during the rover’s first five years on Mars, which enabled measurement of the planet’s gravitational tug on the rover.
Familiar with Apollo 17’s gravimeter, which took a total of 25 measurements on the lunar surface, Lewis took the more than 700 measurements Curiosity’s accelerometer collected between October 2012 and June 2017 and compared them with computer models of Mars’ gravity field and with mineral-density estimates produced by the rover’s Chemistry and Mineralogy instrument, which uses an X-ray beam to determine rocks’ porosity.
“The lower levels of Mount Sharp are surprisingly porous,” Lewis, who published his findings in the journal Science, said in a NASA news release. “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.”
Located within Gale Crater, Mount Sharp is one of the tallest mountains on Mars. Uncertain as to how the mountain formed, some scientists theorize that Gale Crater once held a significant amount of sediment that eroded over time, in part due to wind.
If the whole crater had once been filled, Mount Sharp should have many layers of fine, compacted sediment. Yet data collected indicates the mountain’s lower layers have only half a mile to a mile (one to two kilometers) of this sediment.
Lewis views the Martian landscape as not that different from Earth’s, although different processes shaped the surfaces of the two planets. Earth’s landscape was shaped mostly by water whereas the landscape on Mars was shaped by wind and blowing sand, he said.
From its position in Gale Crater, Curiosity detected the start of the intense global dust storm that engulfed the Red Planet in June 2018. Sensors attached to the motor on the rover’s deck measured a sudden drop in temperature during the Martian daytime due to sunlight being blocked by dust. This situation meant that the dust kept nighttime temperatures higher than usual by preventing the escape of infrared radiation into space.
With a combination of its on board weather station and motor readings, Curiosity successfully tracked the dust storm and predicted its dissipation in mid-September.
Unlike NASA’s Opportunity rover, which is powered by solar panels and went silent in mid-June when the low light levels prevented the panels from charging its batteries, Curiosity was unaffected by the dust storm because it is powered by a plutonium radioisotope thermoelectric generator.
After taking its final selfie on Vera Rubin Ridge, Curiosity traveled to the top of a clay-rich ridge known as Knockfarril Hill, a rubbly region that it will study for the next three Martian days. Following that, it will descend Knockfarril Hill and conduct mobility tests to determine the best driving technique over the rubbly terrain.
The view from Vera Rubin Ridge in January 2018. Video courtesy of NASA’s Jet Propulsion Laboratory
Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.