A planet’s history is told in its ancient rock. Earth’s oldest rocks are in the Canadian Shield, Australia’s Jack Hill, the Greenstone Belts in Greenland, and a handful of other locations. These rocks hold powerful clues to our planet’s history. On Mars, the same holds true.
That’s why NASA’s Perseverance rover is revisiting some of them.
Perseverance is exploring Jezero Crater, an ancient paleolake. Its thick layer of sediments may contain evidence of ancient life on Mars. Every crater has a rim, and Perseverance’s current campaign involves studying the rim. The crater rim is different than the sediments. It’s made of ancient rock uplifted and exposed on the surface by the ancient impact that created Jezero.
On Earth, geologists regularly study rock that has made itself easy to examine by coming up from the deeper crust and presenting itself. The same thing happens on Mars, though impacts do the lifting, not plate tectonics. Perseverance is studying the rocks on the crater rim in its current Crater Rim Campaign. The location it’s exploring is an exposed outcrop named Tablelands.
This image shows Perseverance’s landing ellipse (green circle) and the different regions in the Jezero Crater. The rover is currently exploring the crater rim, shown in purple. Image Credit: NASA/JPL-Caltech/USGS/University of ArizonaOne type of rock that can teach us a lot about Mars’ ancient history is serpentine. It’s common on Earth and Mars and forms in the presence of water. Its presence on Mars is some of our strongest evidence that the planet was once wet.
Perseverance sampled Silver Mountain, a rock in the Tablelands. The rover used its abrasion tool on its robotic arm to create a fresh surface it could analyze. That analysis showed Silver Mountain is rich in pyroxene, a type of silicate found in almost every igneous and metamorphic rock. The rover also collected a core.
After that, it visited a rock named Serpentine Lake that showed telltale signs of serpentine. Perseverance used its abrasion tool to clean the rock for a detailed investigation. Serpentine Lake has an intriguing texture, described in a press release as “cookies and cream.” It’s also high in serpentine and other minerals that form in the presence of water.
Perseverance used its Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) instrument to examine the Serpentine Lake rock. The rock shows a high concentration of serpentine, indicating that it was exposed to water for a long time, a hint of Mars’ potential ancient habitability. Its unusual texture also hints at complex geological processes. Image Credit: NASA/JPL-CaltechAfter that, Perseverance doubled back to revisit a rock named “Cat Arm Reservoir.”
It was the first rock the rover studied on the canyon rim. The rover analyzed its composition and detected coarse pyroxene and feldspar crystals, indicating an igneous origin. Unfortunately, Perseverance’s sample tube was empty. Sometimes, the rock the rover tries to sample is weak and turns to dust. This is rare, but it did happen during the rover’s very first sampling attempt, and it happened again with Cat Arm Reservoir.
This image from NASA’s Perseverance Location Tracker shows the rover’s convoluted path as it explores the rim of Jezero Crater. Image Credit: NASA/JPLPerseverance travelled a small distance and tried to collect a core sample from Cat Arm Reservoir again. That attempt also failed. Then the rover chose a different spot nearby named “Green Gardens” and successfully collected a core sample. It’s next to the abrasion patch on Serpentine Lake.
NASA’s Mars Perseverance rover acquired this image of the area in front of it. It shows the Serpentine Lake abrasion patch on the right-hand side of the rock, with the Green Gardens sampling location on the left. The rover used its onboard Front Right Hazard Avoidance Camera A and captured the image on Feb. 16, 2025 (sol 1420, or Martian day 1,420 of the Mars 2020 mission) at the local mean solar time of 16:45:19. Image Credit: NASA/JPL-CaltechLike the Serpentine Lake rock, Green Garden is also green, which is a characteristic of the mineral serpentine. Serpentine forms in the presence of water when hydrothermal vents alter ultramafic rocks. Scientists are interested in these minerals because their structure and composition can reveal the history of water on Mars. On Earth, serpentine rock also hosts microbial life, so the same may have been true on Mars. Unfortunately, it’s not clear how much evidence of this life can be preserved.
Perseverance’s “Green Garden” core sample was collected on February 17th. Image Credit: NASA/JPL-CaltechPerseverance will spend some more time exploring the Tablelands outcrop. It may re-examine the Serpentine Lake abrasion patch and analyze the debris from the Green Gardens drilling and coring. This could take a couple of weeks.
Next on its agenda is “Broom Point,” further down the crater rim. Broom Point contains a spectacular formation of layered rock, which is also intriguing to scientists.
Mars’ ancient history is told in its ancient rocks, but it’s impossible to know in advance which rock holds which clues and how everything will fall into place.
We don’t know what Perseverance will discover about Broom Point. But the rock will tell us something. It always does.
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Data from the Chinese rover Zhurong is adding to the pile of evidence for oceans on ancient Mars. For a year, this little craft traveled over nearly two kilometers of the Martian surface and made radar scans of buried natural structures that look like ocean shorelines.
Zhurong’s ground-penetrating radar (GPR) looked under the surface to a depth of 80 meters. There, the radar instrument found thick layers of material similar to beach deposits on Earth. The best way to create such formations is by wave action stirring up and depositing sediments along the shore of an ocean. If these findings stand, they’ll provide a deeper look into Mars’s ancient warm, wet past, and the existence of long-gone seas.
Map of Utopia Planitia showing the landing site of the Zhurong rover and four proposed ancient shorelines. The landing site is about 280 kilometers north of and some 500 meters lower in elevation than the northern hypothesized shorelines. In its traverse, Zhurong traveled south from its landing site, toward the ancient shorelines. Courtesy: Hai Liu, Guangzhou University, China Figuring Out Mars Shorelines“The southern Utopia Planitia, where Zhurong landed on May 15, 2021, is one of the largest impact basins on Mars and has long been hypothesized to have once contained an ancient ocean,” said Hai Liu, a professor with the School of Civil Engineering and Transportation at Guangzhou University and a core member of the science team for the Tianwen-1 mission, which included China’s first Mars rover, Zhurong. “Studying this area provides a unique opportunity to investigate whether large bodies of water ever existed in Mars’ northern lowlands and to understand the planet’s climate history.”
At first, scientists considered lava flows or dunes to explain the structures Zhurong measured. But, their shapes say otherwise. “The structures don’t look like sand dunes. They don’t look like an impact crater. They don’t look like lava flows. That’s when we started thinking about oceans,” said Michael Manga, a University of California, Berkeley, professor of earth and planetary science. He was part of Hai’s team that recently published a paper about Zhurong’s findings. “The orientation of these features are parallel to what the old shoreline would have been. They have both the right orientation and the right slope to support the idea that there was an ocean for a long period of time to accumulate the sand-like beach.”
Digging into the PastAside from their meteorological and geological value, the presence of these shoreline structures also implies that Mars’s ancient oceans were ice-free. “To make ripples by waves, you need to have an ice-free lake. Now we’re saying we have an ice-free ocean. And rather than ripples, we’re seeing beaches,” Manga said. That tells us Mars was a warmer world—at least for a while. Rivers could well have flowed across the surface, contributing rocks and sediments along the shorelines. And, of course, there are structures that imply the presence of oceans. On Earth, oceans provide life habitats and there’s no reason to think that Mars oceans couldn’t have done that, too.
“The presence of these deposits requires that a good swath of the planet, at least, was hydrologically active for a prolonged period in order to provide this growing shoreline with water, sediment, and potentially nutrients,” said co-author Benjamin Cardenas, an assistant professor of geosciences at The Pennsylvania State University (Penn State). “Shorelines are great locations to look for evidence of past life. It’s thought that the earliest life on Earth began at locations like this, near the interface of air and shallow water.”
Shoreline Evidence for Changes on MarsAs far back as Viking, scientists had images showing what looked like irregular shorelines and flow features on the surface. Those features implied bodies of water and flowing rivers. Other missions returned images and data showing ponded areas where smaller bodies of water existed. More recent missions returned images of regions scoured and changed by catastrophic floods. The shoreline features imply that oceans existed.
We know today that Mars’s surface no longer hosts bodies of water. In the past, much of it escaped to space along with Mars’ atmosphere. But some water also went underground and remains there as ice deposits. And, some combined with rocks to form new minerals. Other geological features seem to point to the existence of Martian oceans, like the shorelines Zhurong and Viking measured.
Schematic showing how a series of beach deposits would have formed at the Zhurong landing site in the distant past on Mars (left) and how long-term physical and chemical weathering on the planet altered the properties of the rocks and minerals and buried the deposits. Courtesy: Hai Liu, Guangzhou University, ChinaHowever, the irregular shape of those shorelines continued to intrigue planetary scientists. That’s because they didn’t exactly look like shorelines like we see along Earth’s oceans, which are level. In 2007, Manga came up with the idea that the shapes of the shorelines were altered by changes in the planet’s rotation. Why did that happen? Blame it on volcanoes in the Tharsis region. Some 4 billion years ago volcanic activity there built up a huge bulge. That eventually messed with the planet’s rotation. “Because the spin axis of Mars has changed, the shape of Mars has changed. And so what used to be flat is no longer flat,” Manga explained.
If the findings hold up, the buried shorelines tell a compelling story of the last days of oceans on Mars. Based on the team’s paper, that water appears to have lasted tens of millions of years. As it disappeared and the climate dried up, wind-blown regolith covered the shorelines that Zhurong measured.
For now, the Zhurong data provides a look into shoreline deposits that are pristine—but buried under the subsurface. “There has been a lot of shoreline work done,” said Cardenas, “but it’s always a challenge to know how the last 3.5 billion years of erosion on Mars might have altered or completely erased evidence of an ocean. But not with these deposits. This is a very unique dataset.”
For More InformationAncient Beaches Testify to Long-ago Ocean on Mars
Ancient Ocean Coastal Deposits Imaged on Mars
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