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 focused on the clay-rich and sulfate-laden regions for evidence each might offer about Mars’s watery past, the transition zone is also proving to be scientifically fascinating. In fact, this transition can provide the registration of a major change in the climate of Mars billions of years ago that scientists are just beginning to understand.
The clay minerals formed when lakes and streams once flowed through Gale Crater, depositing sediment at what is now the base of Mount Sharp, the 5-kilometre (3-mile)-high mountain whose foothills Curiosity has been climbing since 2014. on the mountain in the transition zone, Curiosity’s observations show that streams dried up and sand dunes formed on top of lake sediments.
“We no longer see the lacustrine deposits that we saw for years further down Mount Sharp,” Ashwin Vasavada, Curiosity project scientist at NASA’s Jet Propulsion Laboratory, said in a statement. “Instead, we see a lot of evidence of drier climates, like dry dunes that occasionally had streams around them. That’s a big change from lakes that persisted for perhaps millions of years before.”
As the rover climbs higher through the transition zone, detects less clay and more sulfate. Curiosity will soon drill the last rock sample it will take from this area, providing a more detailed look at the changing mineral composition of these rocks.
Unique geological features also stand out in this area. The hills in the area likely began in a dry environment of large windswept sand dunes, which hardened into rock over time. Interspersed in the remains of these dunes are other waterborne sediments, perhaps deposited in ponds or small streams that once weaved through the dunes. These sediments now appear as stacks of scaly layers resistant to erosion, like one nicknamed “The Bow.”
What makes the story richer and even more complicated is the knowledge that there were multiple periods when groundwater flowed and flowed over time, leaving a jumble of puzzle pieces for Curiosity’s scientists to assemble into a precise timeline.
Curiosity will celebrate its 10th year on Mars on August 5. While the rover is showing its age after a full decade of exploration, nothing has stopped it from continuing its ascent.
On June 7, Curiosity entered safe mode after detecting a temperature reading on an instrument control box inside the rover’s body that it was hotter than expected. Safe mode occurs when a spacecraft detects a problem and automatically shuts down all but the most essential functions so engineers can assess the situation.
Although Curiosity exited safe mode and returned to normal operations two days later, JPL engineers are still analyzing the exact cause of the problem. They suspect that safe mode kicked in after a temperature sensor provided an inaccurate measurement, and there are no signs that it will significantly affect rover operations, as backup temperature sensors can ensure the electronics inside the rover’s body don’t get too hot.
The rover’s aluminum wheels also show signs of wear. On June 4, the engineering team instructed Curiosity to take new photos of its wheels, something it had been doing every 1,000 meters to check its general condition.
The team found that the left center wheel had sustained damage to one of its claws, the zigzag treads along Curiosity’s wheels. This particular wheel already had four broken claws, so now five of its 19 claws are broken.
Previously damaged claws recently attracted attention online because some of the metal “skin” between them appears to have fallen off the wheel in recent months, leaving a space.
The team has decided to increase the image of the wheels to every 500 meters, a return to the original cadence. A traction control algorithm had reduced tire wear enough enough to justify the increase in the distance between images.
“We have shown through ground tests that we can safely drive on the wheel rims if necessary,” said Megan Lin, project manager for Curiosity at JPL. “If we ever get to the point where a single wheel has broken off most of its claws, we could do a controlled break to shed the pieces that remain. Due to recent trends, it seems unlikely that we will need to take such action. The wheels hold up well and provide the traction we need to continue our ascent.”