Martian Climate Did Not Change From Wet to Dry All at Once

by | Apr 15, 2021 | Curiosity, Daily Space, Mars | 0 comments

IMAGE:View of hillocks on the slopes of Mount Sharp, showing the various types of terrain that will soon be explored by the Curiosity rover, and the ancient environments in which they formed, according to the sedimentary structures observed in ChemCam’s telescope images (mosaics A and B). CREDIT: NASA/JPL-Caltech/MSSS/CNES/CNRS/LANL/IRAP/IAS/LPGN

While much of the press is focused on Perseverance and its little helicopter, Ingenuity, NASA’s Mars Curiosity rover continues to study and explore the Martian surface. In a new study published in the journal Geology, a team of researchers has analyzed images from Curiosity’s ChemCam instrument. These images were taken with the telescopic imager, and they have an unprecedented resolution for the Martian rovers.

Curiosity is currently exploring Mount Sharp, the central sedimentary peak within Gale Crater, Curiosity’s home base, really, and an impact crater from early in our solar system’s history, about 3.5-3.8 billion years ago. Mount Sharp is about 5.5 kilometers high, and it preserves an early record of Martian history that geologists have been waiting to study for years.

With these new images, those geologists have finally had their chance, and what they found shows far more climate change than predicted. We’ve talked here before about how there was water on the surface of Mars, possibly even a small ocean, and then that water disappeared. Earlier studies discussed the possibility that the water had evaporated and escaped the atmosphere due to the lower gravity, while recent studies now show that the water is more likely trapped underground in minerals and even subsurface glacial deposits.

But what were the conditions that lead to the change in the state of the water? Did it all disappear at once or over time? This new paper examined the recent images and found amazing sedimentary structures, in detail, that lead the team to conclude that there were multiple transitions between a wet climate and a dry climate.

Per the press release: Moving up through the terrain, Curiosity observed that the types of bed change drastically. Lying above the lake-deposited clays that form the base of Mount Sharp, sandstone layers show structures indicating their formation from wind-formed dunes, suggesting long, dry climate episodes. Higher up still, thin alternating brittle and resistant beds are typical of river floodplain deposits, marking the return of wetter conditions.

A reminder that we are using a robot on another planet to analyze that planet’s geology down to the details in the layers of different types of rock. These kinds of details are the stuff of sedimentologists’ dreams, and I heard many professors and students gush over them in pictures and in the field during my geology coursework. And we are getting to see them and explain them and understand them on Mars.

The other neat thing about this study is that it uses ChemCam in a way I hadn’t heard about before. I didn’t know it had a telescopic camera. I’m most familiar with it being the instrument that vaporizes rock fragments with a laser beam and then analyzes the plasma to get the composition of the rock. That’s one of the ways we know that the rocks in this area are primarily mudstone and sandstone. Those two types of rock alone would be enough to say there was at least one wet period and one dry but to get in there and see the actual thin layers alternating… amazing stuff.

The plan now is for Curiosity to keep climbing the foothills of Mount Sharp and drill into the various beds to get an even closer look at the materials that make up these layers.

More Information

CNRS press release

GSA press release

Los Alamos National Laboratory press release

Alternating wet and dry depositional environments recorded in the stratigraphy of Mount Sharp at Gale crater, Mars,” W. Rapin et al., 2021 April 8, Geology

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