Martian mudflats hark back to the time the planet dried out
Latest images from Curiosity show first signs of mud cracks that probably came as Martian climate was changing.
NASA's Curiosity rover has imaged a network of cracks in a rock slab called "Old Soaker" that scientists believe was formed by a drying mud layer more than three billion years ago.
They think that the cracks formed at a time when dry intervals were interrupting wetter periods that supported the lakes in the area that Curiosity has previously found evidence for in older, lower-lying rock layers and in younger mudstone above Old Soaker.
"Mud cracks are the most likely scenario here," Curiosity science team member Nathan Stein told reporters, noting it would be the first such evidence the rover had found.
"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. It looks like what you'd see beside the road where muddy ground has dried and cracked."
The team believes that the cracked layer was buried by other layers of sediment, all becoming stratified rock. Later, wind erosion would have stripped stripped away the layers above Old Soaker. Material that had filled the cracks resisted erosion better than the mudstone around it, so the pattern from the cracking now appears as raised ridges.
The target rock's name is copied from an island off the coast of Maine -- with similar island names forming the theme for features in the same area, around Mount Sharp, recorded by the Curiosity crew.
"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," says 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."
The rover landed near Mount Sharp in 2012 and reached the base of the mountain in 2014. Rock layers forming the base of the mountain accumulated as sediment within ancient lakes billions of years ago. Data collected by Curiosity suggests that ancient Martian lakes offered conditions that would have been favourable for microbes. Curiosity is now investigating how and when the habitable ancient conditions evolved into the more hostile conditions of today.
Further reading: Curiosity’s view of life on Mars