NASA’s Curiosity rover has discovered unusual shallow holes dotting the bedrock inside Gale Crater on Mars. As the rover climbs Mount Sharp, mission scientists are investigating these tiny divots and nearby complex boxwork formations that stem from ancient groundwater activity.
Exploring a dried-up crater lake millions of miles from Earth, NASA’s Curiosity rover has been tirelessly exploring for 14 years. In that time, it’s seen surprising minerals, interesting rock textures, red noons and blue sunsets, and even eclipses involving Mars’s two moons. Even after all this time, however, the rover can still roll up to a new way Mars has found to be weird – something that defies easy explanation.
While pitted ground is hardly a newcomer to a planet regularly pelted by meteorites, these latest features stand out for their unusual geometry. Usually, small pits in the bedrock can be explained fairly readily when pebbles or mineral nodules embedded in softer rock resist erosion for longer than their surrounding substrate before eventually weathering out and leaving little cavities behind. The new pits are different because they are unusually broad and shallow, with the hole pictured measuring about 1 centimeter (0.4 inches) across, and there are no obvious pebbles or nodules nearby that look as though they once occupied them.
Closer Inspection in Valle Grande
To untangle the formation mechanism behind the mysterious pits found while climbing through Valle Grande, a broad valley cutting through the sulfate-rich layers of Mount Sharp, mission operators deployed the rover’s onboard imaging suite. Curiosity’s Mars Hand Lens Imager, or MAHLI, photographed the pits at close range, while its Mastcam cameras captured overlapping stereo images of the surrounding terrain. Researchers combine these images to build three-dimensional models of the surface, allowing scientists to measure the pits’ shapes and depths and, hopefully, work backward to how they formed.
This investigation unfolds against the backdrop of a major mission milestone. In late August 2026, the rover marked an elevation gain of 1,000 meters (3,280 feet) during its ascent. The peak of Mount Sharp rises 5.5 kilometers (3.4 miles) above the crater floor, serving as a vertical timeline where sedimentary layers preserve records of different periods of deposition across the red planet’s geological history. As the rover climbs, the researchers also noticed rapid changes in the appearance of successive rock beds, including rougher gray layers that resist erosion differently from neighboring material, prompting Curiosity to sample the chemistry.
Groundwater Echoes in Spiderweb Boxwork
Before encountering the shallow pits, earlier this year the rover left behind strange, web-like “boxwork” terrain it had spent months investigating—a landscape of resistant mineralized ridges thought to have been shaped by groundwater billions of years ago. While these structures appear as vast, web-like patterns when viewed from orbit, they resolve into low ridges and hollows, typically standing 1–2 metres high and crisscrossing the landscape for miles, from the rover’s surface-level perspective.
This structural evidence points to the presence of liquid water on this part of the Red Planet much later than scientists previously believed.
“Seeing boxwork this far up the mountain suggests the groundwater table had to be pretty high,” says Tina Seeger, one of the mission scientists leading the investigation.
Seeger added, And that means the water needed for sustaining life could have lasted much longer than we thought looking from orbit.
Researchers are still trying to understand the bumpy nodules formed by minerals that remained as groundwater dried out, noting they can’t quite explain yet why the nodules appear where they do, though maybe the ridges were cemented by minerals first, and later episodes of groundwater left nodules around them.
Unlocking Ancient Martian Climates
The transition from the web-like boxwork terrain as Curiosity works its way through the layered sulfate rocks above gives researchers a record of changing conditions on ancient Mars. The newly discovered strange holes add another layer of mystery, as they could be the result of an unfamiliar process, and further analysis of the chemistry data will take more time. As Curiosity continues its ascent up Mount Sharp, the science team balances ongoing chemical sampling with the investigation of the pits to tell us how a once-wet environment transformed into the dry world we see today.
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