Pictures of boulders that were carried by flash floods into a lake bed might not seem too thrilling.
But when it’s the Perseverance rover photographing the Martian landscape and capturing evidence of dramatic weather events — and perhaps a climactic change — that occurred on this now-desolate planet billions of years ago, the images are indeed intriguing.
The rover landed in the windswept, barren Jezero Crater, which was once a lake linked to a river.
It shot photos of terrain as far away as 1.4 miles, using the SuperCam that Los Alamos National Laboratory helped develop for the Mars mission. Some of the images and an analysis by almost 40 researchers were published in the journal Science.
This glimpse into Mars’ wetter period of roughly 3.7 billion years ago is compelling because it coincides with the time when the Earth had only single-cell life forms, said Roger Wiens, the lab’s principal investigator for SuperCam.
The two planets formed at about the same time, as did others in the solar system, but they evolved much differently over eons, Wiens said. Mars is a mystery that is slowly unveiling, and each bit of new evidence like this offers scientists greater insight into the red planet, he said.
“The long-term exploration we’re trying to do now is how habitable was Mars, how long were the time periods for the lakes, what was the climate like?” Wiens said.
Another question is whether there are organic materials in the area, Wiens said.
Researchers believe the most likely place for such fossils would be in the crater’s bottom sedimentary layer, formed from mud and sand deposits.
As always, discovering places on Mars that contained water raises the question of what kind of organisms might have thrived there, because water is a key source of life.
Photographic evidence of the planet having expansive water bodies long ago is nothing new. Previous rovers snapped pictures of a giant, desiccated lake bed and crevices that formed on the surface when a lake system dried up and the mud floors cracked en masse.
It’s generally believed that Mars’ atmosphere is too thin to hold water. Some scientists think the planet’s lack of a protective electromagnetic field allowed the solar wind to severely deplete the atmosphere.
What’s different about the Perseverance images is they’ve zoomed into the site of a once-dynamic Martian water system.
The Science paper describes signs of a river depositing sediments at a delta near the lake and then later heavy flooding that scooped up two dozen mammoth boulders miles away and carried them into the water body.
The boulders’ location shows the lake wasn’t full at the time of the massive floods, perhaps indicating a shift in climate, Wiens said.
Scientists can only speculate about what caused floods large enough to sweep up boulders that weigh several tons each.
Wiens said torrential rainstorms might have swelled the rivers or an ancient glacier might have melted. And around 3 billion years ago, Mars shut down and became uninhabitable while life on Earth continued to burgeon, he said.
Mars’ extremely dry conditions make it able to preserve geological artifacts and organic traces, known as biosignatures, much longer than Earth can; Earth is warm, watery and ever-changing, Wiens said.
A NASA scientist agreed that Mars has far more geological remnants that are billions of years old than Earth does.
“It is very rare to find rocks on Earth that are this old,” said Katie Stack Morgan, deputy project scientist on the Mars rover mission. “On Mars, we have vast provinces of rocks of this age.”
Earth, unlike Mars, has tectonics that lead to its crust constantly recycling, Stack Morgan said.
Mars appears to have been dynamic in the distant past, similar to how Earth is now, making it worth investigating what that planet was really like back then, she said.
And being able to study such diverse planetary materials from so far in the past is valuable, she said.
“This gives us a chance to learn something fundamentally new about the solar system — not just Mars, but also this period when our planet was becoming habitable,” Stack Morgan said.
SuperCam’s remote micro-imager captured terrestrial features confirming rivers flowed into a lake that is now Jezero Crater, a big contribution to the Mars mission, Stack Morgan said.
The camera also will help scientists learn about where the rover collects samples and whether they were in a younger or older area of Mars, she said, noting that it’s better to determine those facts before hauling the stuff to Earth.
Linking the various samples gathered from, say, the crater will help create a clearer narrative of that area, Stack Morgan said.
“SuperCam … can provide the connections between the samples and tell us how those samples relate to each other,” she said, “which will make the science we do when they come back [to Earth] all the more powerful and meaningful.”