“To me, Mars is the uncanny valley of Earth,” said planetary geophysicist Kevin Lewis of Johns Hopkins University. “It’s similar but was shaped by different processes. It feels so unnatural to our terrestrial experience.”
In a 2019 paper in Science, NASA 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 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 much lower than expected.
Three times higher than the Grand Canyon is deep
Because of its history, the 96-mile wide Gale Crater crater with its strangely sculpted mountain towering three times higher than the Grand Canyon is deep–is the ideal place for Curiosity to conduct its mission of exploration into the Red Planet’s past. Researchers use Curiosity to study layers in the mountain that hold evidence about wet environments of early Mars.
“This may be one of the thickest exposed sections of layered sedimentary rocks in the solar system,” said Joy Crisp, MSL Deputy Project Scientist from NASA’s Jet Propulsion Laboratory. “The rock record preserved in those layers holds stories that are billions of years old — stories about whether, when, and for how long Mars might have been habitable.”
“Smartphone” Sensors to the Rescue
Moving your smartphone allows 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 coincidence, the rover’s accelerometers can be used like 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 as scientists expected.
“The lower levels of Mount Sharp are surprisingly porous,” said lead author Lewis. “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.”
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 compared to models of Mars’ 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 porous the rocks are.
Mountain of Mystery
There are many mountains within craters or canyons on Mars, but few approach the scale of Mount Sharp. Scientists still aren’t sure how the mountain grew inside of Gale Crater. One idea 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 should 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 kilometers) – much less than if the crater had been completely filled.
“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. 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’re planetary siblings, at once familiar and starkly different.
New ChemCam Data –Stark Periods of Wet and Dry
Researchers at the Los Alamos National Laboratory in April 2021, announced that based on detailed observations of the long-range camera on Curiosity rover’s ChemCam of the steep terrain of Mount Sharp discovered that the Martian climate alternated between dry and wetter periods before it went completely dry. Lying above the lake-deposited clays that form the base of Mount Sharp, sandstone layers show structures indicating their formation from wind-formed dunes, suggesting long, dry climate episodes. Higher up still, thin alternating brittle and resistant beds are typical of river floodplain deposits, marking the return of wetter conditions.
View of the slopes of Mount Sharp, showing the various types of terrain that have been and will be explored by the Curiosity rover. The sedimentary structures observed by ChemCam’s telescopic images (mosaics A and B) reveal clues about the ancient environments in which they formed. NASA/JPL-Caltech/MSSS/CNES/CNRS/LANL/IRAP/IAS/LPGN
The NASA image at the top of the page shows the region around Gale Crater, which Mars Science Laboratory’s Curiosity rover is currently exploring. This mosaic is made from Thermal Emission Imaging System (THEMIS) images used to pick out distinct surface mineralogies. Pink indicates wind-blown dust, purple basaltic rocks. Mars’s surface typically appears grey-green; the blue tones of Gale Crater’s central Mount Sharp.
Editor, Jackie Faherty, astrophysicist, Senior Scientist with AMNH. Jackie was formerly a NASA Hubble Fellow at the Carnegie Institution for Science. Aside from a love of scientific research, she is a passionate educator and can often be found giving public lectures in the Hayden Planetarium. Her research team has won multiple grants from NASA, NSF, and the Heising Simons foundation to support projects focused on characterising planet-like objects. She has also co-founded the popular citizen science project entitled Backyard Worlds: Planet 9 which invites the general public to help scan the solar neighbourhood for previously missed cold worlds. A Google Scholar, Faherty has over 100 peer reviewed articles in astrophysical journals and has been an invited speaker at universities and conferences across the globe. Jackie received the 2020 Vera Rubin Early Career Prize from the American Astronomical Society, an award that recognises scientists who have made an impact in the field of dynamical astronomy and the 2021 Robert H Goddard Award for science accomplishments.