Curiosity's View of Sulfate-Bearing Region and Streambed Rocks: NASA’s Curiosity Mars rover captured this view of a sulfate-bearing region using its Mastcam on May 2, 2022, the 3,462nd Martian day, or sol, of the mission. Dark boulders seen near the center are thought to have formed from sand deposited in ancient streams or ponds. Credits: NASA/JPL-Caltech/MSSS. Download image ›
Striking rock formations documented by the rover provide evidence of a drying climate in the Red Planet’s ancient past.
For the past year, NASA’s Curiosity Mars rover has been traveling through a transition zone from a clay-rich region to one filled with a salty mineral called sulfate. While the science team targeted the clay-rich region and the sulfate-laden one for evidence each can offer about Mars’ watery past, the transition zone is proving to be scientifically fascinating as well. In fact, this transition may provide the record of a major shift in Mars’ climate billions of years ago that scientists are just beginning to understand.
The clay minerals formed when lakes and streams once rippled across Gale Crater, depositing sediment at what is now the base of Mount Sharp, the 3-mile-tall (5-kilometer-tall) mountain whose foothills Curiosity has been ascending since 2014. Higher on the mountain in the transition zone, Curiosity’s observations show that the streams dried into trickles and sand dunes formed above the lake sediments.
“We no longer see the lake deposits that we saw for years lower on Mount Sharp,” said Ashwin Vasavada, Curiosity’s project scientist at NASA’s Jet Propulsion Laboratory in Southern California. “Instead, we see lots of evidence of drier climates, like dry dunes that occasionally had streams running around them. That’s a big change from the lakes that persisted for perhaps millions of years before.”
As the rover climbs higher through the transition zone, it is detecting less clay and more sulfate. Curiosity will soon drill the last rock sample it will take in this zone, providing a more detailed glimpse into the changing mineral composition of these rocks.
Unique geologic features also stand out in this zone. The hills in the area likely began in a dry environment of large, wind-swept sand dunes, hardening into rock over time. Interspersed in the remains of these dunes are other sediments carried by water, perhaps deposited in ponds or small streams that once wove among the dunes. These sediments now appear as erosion-resistant stacks of flaky layers, like one nicknamed “The Prow.”
Making the story richer yet more complicated is the knowledge that there were multiple periods in which groundwater ebbed and flowed over time, leaving a jumble of puzzle pieces for Curiosity’s scientists to assemble into an accurate timeline.