Among other discoveries made by the rover, wavy rock textures suggest that lakes existed in an area of ​​ancient Mars that scientists expected to be drier. When NASA’s Curiosity rover arrived at the “sulphate-bearing unit” last fall, scientists thought they had seen the last evidence that lakes once covered this region of Mars.
This is because the rock layers formed here in a drier environment than the areas explored earlier in the mission. It is believed that the local sulfates – salty minerals – remained here when the water dried to a trickle.
So the Curiosity team was surprised to discover the mission’s clearest evidence yet of ancient water waves forming in lakes. Billions of years ago, waves on the surface of a shallow lake stirred up the sediment on the lake floor, creating the undulating textures left in the rock over time.
This is the best evidence of water and waves we’ve seen during the entire mission,” said Ashwin Vasavada, Curiosity’s project scientist at NASA’s Jet Propulsion Laboratory in Southern California. “We’ve crawled through thousands of feet of lake sediment and never seen evidence like this – and now we’ve found it in a place we expected to be dry.”
Layers of history
Since 2014, the rover has been climbing the base of Mount Sharp, a 3-mile-high (5-kilometer-high) mountain that was once laced with lakes and streams that would have provided a rich environment for microbial life, if there ever was one. originated on the Red Planet.
Mount Sharp is made up of layers, with the oldest at the base of the mountain and the youngest at the top. As the rover ascends, it progresses along the Martian timeline, allowing scientists to study how Mars evolved from a more Earth-like planet in its ancient past, with a warmer climate and abundant water, to the frigid desert it is today.
After climbing nearly half a mile above the base of the mountain, Curiosity found these undulating rock textures preserved in what is dubbed the “Marker Band” — a thin layer of dark rock that juts out from the rest of Mount Sharp.
This rock layer is so hard that Curiosity was unable to drill a sample from it after several attempts. It’s not the first time Mars has been unwilling to share a sample: Lower the mountain on the “Vera Rubin Ridge” Curiosity had to try three times before finding a place soft enough to drill.
Scientists will be looking for softer rock in the coming week. But even if they never get a sample from this unusual band of rock, there are other places they want to explore.
Martian footprints
Far beyond the Marker Band, scientists can see another clue to the history of ancient water on Mars in a valley called Gediz Vallis. The wind carved the valley, but the channel that runs through it and starts higher on Mount Sharp was probably eroded by a small river. Scientists believe there were also wet landslides that sent car-sized boulders and debris to the valley floor.
Because the resulting debris pile overlies all the other layers in the valley, it is clearly one of the youngest formations on Mount Sharp. Curiosity spotted this debris in the Gediz Vallis Ridge twice last year, but could only examine it from a distance. The rover team hopes to have another chance to view it later this year.
Another clue within the Marker Band that fascinated the team is an unusual rock texture likely caused by some kind of regular weather or climate cycle, such as dust storms. Near undulating textures are rocks made up of layers that are regular in their spacing and thickness.
This kind of rhythmic pattern in the Earth’s rock layers often stems from atmospheric events that happen at regular intervals. It is possible that the rhythmic patterns in these Martian rocks resulted from similar events that indicated changes in the ancient climate of the Red Planet.
“The waves, the debris flows, and the rhythmic layers all tell us that the wet-to-dry story on Mars was not a simple one,” Vasavada said. “The ancient climate of Mars had an amazing complexity, similar to that of Earth.”
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