NASA’s Curiosity rover studies possible mud cracks
Researchers with NASA’s Curiosity mission have recently been using the Mars rover to study slabs of rock cross-hatched with shallow ridges that may have begun as cracks in drying mud more than 3 billion years ago. If this interpretation is confirmed, these would be the first mud cracks, also known as desiccation cracks, that Curiosity has found. The cracks would indicate that the ancient era when these sediments were deposited included some drying after wetter conditions.
“Mud cracks are the most likely scenario here,” said Curiosity science team member and Caltech graduate student Nathan Stein, who led the investigation of the site called “Old Soaker” on lower Mount Sharp. “Even from a distance, we could see a pattern of four- and five-sided polygons that don’t look like fractures we’ve seen previously with Curiosity,” Stein said. “It looks like what you’d see beside the road where muddy ground has dried and cracked.”
The cracked layer formed over 3 billion years ago and was later buried by other layers of sediment, all becoming stratified rock. Wind erosion then stripped away the layer above Old Soaker. Because the material that had filled the crack resisted erosion better than the surrounding mudstone, so the pattern from cracking now appears as raised ridges.
The researchers used Curiosity to study the crack-filing material. Cracks that formed on the surface, such as in drying mud, usually fill with windblown sand. A different type of cracking, one that Curiosity has found evidence of before, occurs after sediments have hardened into rock.
Pressure from the accumulation of many layers of sediments can cause underground fractures in the rock. These fractures are usually filled by minerals delivered by groundwater circulating through the cracks, such as bright veins of calcium sulfate.
Curiosity observed both kinds of crack-filing materials at Old Soaker. This indicates multiple generations of fracturing. First mud cracks, with sediment accumulating in them, then a period of underground fracturing and vein forming.
“If these are indeed mud cracks, they fit well with the context of what we’re seeing in the section of Mount Sharp Curiosity has been climbing for many months,” said Curiosity Project Scientist Ashwin Vasavada of NASA’s Jet Propulsion Laboratory in Pasadena. “The ancient lakes varied in depth and extent over time, and sometimes disappeared. We’re seeing more evidence of dry intervals between what had been mostly a record of long-lived lakes.”
Curiosity has moved on from the Old Soaker site, driving uphill toward a future rock drilling site. Engineers at JPL are still working to determine the best way to resume use of the rover’s drill. In December, Curiosity experienced intermittent problems with its drill feed mechanism.
Jim Sharkey is a lab assistant, writer and general science enthusiast who grew up in Enid, Oklahoma, the hometown of Skylab and Shuttle astronaut Owen K. Garriott. As a young Star Trek fan he participated in the letter-writing campaign which resulted in the space shuttle prototype being named Enterprise. While his academic studies have ranged from psychology and archaeology to biology, he has never lost his passion for space exploration. Jim began blogging about science, science fiction and futurism in 2004. Jim resides in the San Francisco Bay area and has attended NASA Socials for the Mars Science Laboratory Curiosity rover landing and the NASA LADEE lunar orbiter launch.