Alone in a dried-up crater lake millions of miles from Earth, NASA's Curiosity rover has been tirelessly exploring for 14 years, according to Science Alert.
In that time, it's seen the good, the bad, and the ugly of what Gale Crater has to offer. Surprising minerals. Interesting rock textures. Red noons and blue sunsets. Heck, even 'eclipses' involving Mars's two moons.
The rugged terrain holds many secrets that tell scientists about the red planet's geological history, and most of the oddities discovered get an explanation sooner or later.
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.
This time, it's holes.
They were found dotting the ground while Curiosity climbed through Valle Grande, a broad valley cutting through the sulfate-rich layers of Mount Sharp that rises in the middle of the crater.
Holes and pitted ground on Mars are nothing new. Anywhere with geology and a history of getting smacked with meteorites is going to have holes. But these holes – tiny, shallow divots in the ground – are unlike anything seen before on Mars.
Usually, small pits in the bedrock can be explained fairly readily. 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. They're unusually broad and shallow, and there are no obvious pebbles or nodules nearby that look as though they once occupied them.
So Curiosity's science team decided to take a closer look.
The rover'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.
Those images can be combined 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.
The mystery is particularly intriguing because Curiosity is currently driving through relatively fresh territory.
