NASA’s Curiosityrover has started drilling into a bizarre landscape on ?? ??? ??Marsthat could upend assumptions about when the Red Planet truly dried out. 

After a long drive, the Mini Cooper-sized robot reached a so-called boxwork region, where a gridlike pattern of ridges splays over six to 12 miles. For years, orbiters had observed this area from spacebut never up close. 

Scientists had hypothesized before the rover arrived that the peculiar ridges formed with the last trickles of water in the region before it dried out for good. But mineral veins discovered in the boxwork suggest groundwater stuck around longer than anyone expected. 

The bedrock between the ridges contains tiny white veins of calcium sulfate, a salty mineral left behind as groundwater seeps into rock cracks. Deposits of the material were plentiful in lower rock layers from an earlier Martian period. But no one thought they'd appear in the layer Curiosity is exploring now, which formed much later. 

"That’s really surprising," said Curiosity’s deputy project scientist, Abigail Fraeman, in a statement. "These calcium sulfate veins used to be everywhere, but they more or less disappeared as we climbed higher up Mount Sharp. The team is excited to figure out why they’ve returned now."

Ancient Marsused to be wetter — flush with rivers, lakes, and maybe even oceans— but over billions of years, it turned into a dusty, cold desert. What’s unclear is when that shift happened and how long conditions suitable for life might have lingered. Curiosity’s new findings complicate what scientists thought they knew about the timeline.

The rover has spent more than a decade in Gale Crater climbing Mount Sharp, reading the rock layers like pages in a planetary chronicle. The layer it’s on now is chock-full of magnesium sulfates, salty minerals that typically form as water evaporates. That fits the narrative researchers had expected: This was supposed to be a chapter when Marswas well on its way to arid.

That's why a new sample Curiosity drilled this month, dubbed Altadena, could be enlightening. As the rover analyzes the boxwork's composition, scientists may gain a better understanding of how it formed, what minerals are present, and whether any clues about ancient single-celled microorganismsmight be hidden there. The rover will drill more ridges in the coming months to compare them and evaluate how groundwater may have changed over time.

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The mission’s next targets lie farther into the boxwork region, where the patterns grow larger and more distinct. Curiosity will keep looking for organic molecules and other potential evidence of a habitable environment in Mars' ancient past.

The rover team has begun nicknaming features after places near Bolivia’s Salar de Uyuni, one of the driest, saltiest places on Earth. It's reminiscent of the Martian landscape Curiosity is sightseeing today. 

"Early Earth microbes could have survived in a similar environment," said Kirsten Siebach, a rover scientist based in Houston, in an earlier statement. "That makes this an exciting place to explore."