The Mars exploring Curiosity rover has discovered convincing evidence of ancient groundwater. NASA revealed on Monday that the robotic geologist came across crisscrossing low ridges, some just a few inches tall, on the foothills of Mount Sharp in the Gale Crater, where it landed in 2012.

Exploring an area previously only seen from orbit, the Curiosity rover has found dramatic new evidence of ancient groundwater. The rover is using its drill to snag samples of rock that will give geologists new clues to how this area formed. https://t.co/2qQR169QeE pic.twitter.com/zZJzaMwW8H — NASA Mars (@NASAMars) June 23, 2025

These ridges are said to be arranged in what scientists call a boxwork pattern and the bedrock below these ridges likely formed when groundwater trickling through the rock left behind minerals. While the oceans dried and the rocks got eroded, the minerals stayed hardening the ridges. According to NASA, this is the only region where such ridges have been found by Curiosity. Not even orbiters circling Mars were able to spot them.

Curiosity’s current exploration site which may have formed by groundwater billions of years ago. Image: NASA/JPL

“A big mystery is why the ridges were hardened into these big patterns and why only here,” Ashwin Vasavada, Curiosity’s project scientist at NASA’s Jet Propulsion Laboratory (JPL), said in a statement. “As we drive on, we’ll be studying the ridges and mineral cements to make sure our idea of how they formed is on target.”

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Curiosity’s team believes the rover is essentially “time travelling” as different layers of rocks at Mount Sharp were formed during different eras – most of them when the planet still had liquid water. Its current exploration region has a layer with an abundance of salty minerals called magnesium sulfates, which form as water dries up. Besides, scientists say the boxwork patterns suggest that underground water was available on Mars long after the drying process began.

What they’ve found so far is that the boxwork ridges have a different composition than other layers of Mount Sharp and there are lots of tiny fractures filled with white veins of calcium sulfate, another salty mineral left behind as groundwater trickles through rock cracks.

In the current phase, Curiosity will next pulverise the collected rock sample for detailed analysis and search for organic molecules and other evidence of an ancient habitable environment preserved in the cemented ridges.

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(Image: NASA)