NASA’s Curiosity Rover Finds First Traces Of A Fossil Lake On Mars

When NASA’s Curiosity rover exploring Gale Crater, a large impact basin in the equatorial region of Mars, arrived at the “sulfate-bearing unit” last fall, scientists thought they’d seen the last evidence that lakes once covered this region of Mars. That’s because the rock layers here formed in drier settings than regions explored earlier in the mission. The area’s sulfates – salty minerals – are thought to have been left behind when water was drying to a trickle.

So Curiosity’s team was surprised to discover the mission’s clearest evidence yet of ancient lakes surviving for much longer than previously thought. Billions of years ago, waves on the surface of a shallow lake stirred up sediment at the lake bottom, over time creating rippled textures left in rock. Ripple marks are also found on Earth and are common along the seashore or bottom of shallow lakes.

“This is the best evidence of water and waves that we’ve seen in the entire mission,” said Ashwin Vasavada, Curiosity’s project scientist at NASA’s Jet Propulsion Laboratory in Southern California. “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.”

Curiosity has found these rippled rock textures preserved in what’s nicknamed the “Marker Band” – a thin layer of dark rock that stands out from the rest of Mount Sharp – the central peak within Gale Crater. This rock layer is so hard that Curiosity hasn’t been able to drill a sample from it despite several attempts. Scientists will be looking for a spot of softer rock in the week ahead.

One more clue within the Marker Band that has fascinated the team is an unusual rock texture likely caused by some sort of regular cycle in the weather or climate, such as dust storms. Not far from the rippled textures are rocks made of layers that are regular in their spacing and thickness. This kind of rhythmic pattern in rock layers on Earth often stems from atmospheric events happening at periodic intervals. It’s possible the rhythmic patterns in these Martian rocks resulted from similar events, hinting at changes in the Red Planet’s ancient climate.

Material provided by the Jet Propulsion Laboratory.

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