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Jezero Crater, the rover’s exploration site on Mars, was a calm lake 3.7 billion years ago. A small river fed into the lake, sometimes causing flash floods so forceful that it could carry large boulders miles upstream and drop them into the lake. The massive rocks are still there today.
The new information shows the importance of sending rovers to explore the surface of Mars. Previous images captured by the orbiters had shown that this outcrop resembled the kind of fan-shaped river deltas we have on Earth. Perseverance images show definitive proof of the existence of the river delta.
“It helps us better understand the water cycle on Mars,” Amy Williams, study co-author and University of Florida astrobiologist, said in a statement. “From the orbital images, we knew it must be water that formed the delta, but having these images is like reading a book instead of just looking at the cover. I’ll never be able to go to Mars and do this work in person. Seeing these rocks like I would in real life, looking at them, is really amazing and really beautiful. ”
When Perseverance landed at Jezero Crater on February 18, it was just over a mile from the delta. Before the rover’s wheels began to spin, it immediately began taking photos and sending them back to the science team at Perseverance on Earth, like high science-value Martian postcards.
The images showed tilted layers of sediment that were likely created by the flow of water, rather than even flat layers that would have been caused by wind or other processes.
The upper layers of the delta outcrop include large boulders, some as wide as 3.2 feet (1 meter) in diameter and likely weighed several tons. Given their location on the top layer of sediment, they must have come from outside the crater. Scientists believe they came from bedrock on the rim of the crater – otherwise, they came 40 miles or more upstream from the lake.
But flash floods, flowing at speeds of up to 9 meters (29.5 feet) per second, could have washed them away.
“You need energetic flood conditions to transport rocks this big and heavy,” said Benjamin Weiss, study author and professor of planetary science in the Department of Earth, Atmospheric and Planetary Sciences. from the Massachusetts Institute of Technology, in a statement. “It’s a special thing that may indicate a fundamental change in local hydrology or perhaps the regional climate on Mars.”
The fact that the large boulders rest on thin layers of sloping sediment also illustrates that the lake was largely calm until it was hit by flash floods before it dried up. Then billions of years of wind eroded the dry lake bed and the delta.
“The most surprising thing that emerges from these images is the potential opportunity to capture the moment this crater went from an Earth-like habitable environment to this desolate landscape we now see,” Weiss said. “These rock beds may be records of this transition, and we haven’t seen this in other places on Mars.”
While the cause of this climate change remains unknown, the rocks could tell the tale – part of a larger story about why the Martian climate has changed from hot and humid to cold and dry.
“If you look at these footage, you’re basically looking at this epic desert landscape. It’s the most desolate place you can visit,” Weiss said. “There isn’t a drop of water anywhere, and yet here we have evidence of a very different past. Something very profound has happened in the history of the planet.”
A key part of Perseverance’s mission is not just to explore the crater and delta of the river, but to collect intriguing rock samples across both. Future missions will return more than 30 of these samples to Earth by the 2030s. Samples could reveal if life ever existed on ancient Mars – and these new images can help scientists determine the best rocks to sample as they search for evidence of ancient fossils of microbes.
“We now have the opportunity to search for fossils,” Tanja Bosak, study co-author and professor of geobiology at MIT, said in a statement. “It will take some time to get to the rocks that we are really hoping to sample for signs of life. So it’s a marathon, with a lot of potential.”
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