NASA’s Curiosity rover has spotted a set of unusual holes on Mars that appear different from the impact craters typically left by meteorites. The broad, shallow pits were found in Valle Grande, a wide valley cutting through Mount Sharp inside Gale Crater.
While meteorites regularly strike Mars and create craters, scientists are unsure how these particular pits formed. Dr Michelle Minitti, Mars Hand Lens Imager (MAHLI) Deputy Principal Investigator, said the section of rock appeared to have been affected by processes that scientists hope to understand better through further study.
On Earth, similar holes can form when a harder object becomes embedded in softer bedrock and is later washed away or breaks apart, leaving an impression. However, scientists did not find any objects that could have created the Martian pits.
“The pits of this week were much broader and shallower than past features and were not accompanied by obvious objects that were once in the pits,” Minitti wrote in a blog post.
The pits were closely photographed by Curiosity’s Mars Hand Lens Imager, while its Mastcam camera captured overlapping images of the surrounding area. Scientists will use the images to build a three-dimensional map of the pits and measure their shape and depth, which could help determine how they formed.
The rover also observed rapid changes in the appearance of nearby rock layers. Some harder, grey areas appear to resist erosion differently from the surrounding rock. Scientists believe this could indicate that the environmental conditions under which the layers were deposited changed rapidly millions or billions of years ago.
The region is of particular interest because Gale Crater is believed to have formed from an asteroid impact around three billion years ago. Mount Sharp rises 5.5 km from the centre of the crater, with its sedimentary layers thought to preserve a record of the environmental conditions that existed when each layer was deposited.