Billions of years ago, a Martian river flowed with such force that it tumbled boulders in its path, strewing them out into its massive delta. University of Florida astrobiologist Amy Williams looked up from the bed of that ancient river to its rocky remnants, courtesy of the Mars Perseverance rover, which sends on-the-ground views of the red planet back to Williams and the rest of the NASA team.

To Williams, Ph.D., the rock layers looked familiar, matching patterns she’d seen in her fieldwork on Earth — thus revealing how the delta in Mars’ Jezero Crater formed. That discovery, published in the journal Science today, will help scientists pinpoint where to look for signs of ancient life. 

“It’s hugely useful for the mission and guiding us to select samples for return to Earth,” said Williams, an assistant professor of geology at UF. “We’re applying all of our usual tool sets as geologists to understand what these layers mean. It’s amazing to me that you can do that on another world.”

The images reveal a transition from a river flowing into a lake to episodic torrents of floodwater that deposited the boulders. 

“It helps us understand so much more about the water cycle on Mars,” Williams said. “From orbital images, we knew it had to be water that formed the delta, but having these images is like reading a book instead of just looking at the cover.”

Perseverance is Williams’ second Mars mission: She has served on the Curiosity rover team since 2009. The Perseverance rover landed in February 2021 and has been sending high-resolution images back to a multinational team that evaluates them for clues to Mars’ past climate and habitability. Future missions will bring samples back to Earth to search for signs left behind by life on Mars.

“This is the closest I will ever get to going to Mars and doing this work in person,” Williams said. “Seeing these rocks as I would in real life, looking up at them, is really staggering and really beautiful.”