NASA's Curiosity rover discovered wave-rippled rock textures on Mars, suggesting ancient lakes existed in a region scientists expected to be drier.
"This is the best evidence of water and waves that we've seen in the entire mission," Ashwin Vasavada, Curiosity's project scientist at NASA's Jet Propulsion Laboratory in Southern California, said Thursday in a news release.
The rover has been on the Red Planet since 2012; and since 2014, NASA said, it has been ascending the foothills of Mount Sharp, a 3-mile-high mountain that was once laced with lakes and streams that would have provided a rich environment for microbial life.
When Curiosity arrived at the mountain's "sulfate-bearing unit" last fall, NASA said scientists thought they had seen the last evidence that lakes once covered the region because the rock layers there formed in drier settings than other explored regions. The area's sulfates — salty minerals — were thought to have been left behind when water was drying to a trickle.
But the rover, which has climbed a half-mile above Mount Sharp's base, sent back pictures of rippled rock textures. NASA said billions of years ago, waves on the surface of a shallow lake stirred up sediment at the bottom, over time creating rippled textures left in the rock.
"We climbed through thousands of feet of lake deposits and never saw evidence like this — and now we found it in a place we expected to be dry," Vasavada said.
NASA said the rippled rock textures were found in an area known as the "Marker Band" — a thin layer of dark rock that stands out from the rest of Mount Sharp. The rock layer is so hard, Curiosity hasn't been able to drill a sample from it, despite several attempts. Scientists will be looking for softer rock in the week ahead, NASA said.
The space agency said the "Marker Band" has also fascinated scientists because of an unusual rock texture likely caused by a regular cycle in the weather or climate, such as dust storms. There is a rhythmic pattern in rock layers that on Earth would often stem from periodic atmospheric events. It's possible the rhythmic patterns in the Martian rocks resulted from similar events, hinting at changes in the planet's climate.
"The wave ripples, debris flows, and rhythmic layers all tell us that the story of wet-to-dry on Mars wasn't simple," Vasavada said. "Mars' ancient climate had a wonderful complexity to it, much like Earth's."