Footprints found on Mars? Weird 1cm marks spotted by NASA's Curiosity rover; scientists puzzled about geological mystery

NASA’s Curiosity rover has been exploring Mars for more than a decade, studying its rocks, soil and landscape to help scientists understand how the Red Planet changed over time. Even after years of observations, Mars continues to produce unusual geological features, and Curiosity’s latest discovery is another example. The rover has photographed a group of tiny marks on Mount Sharp that, at first look, appear surprisingly similar to footprints.

The formations are actually shallow pits in the Martian bedrock, measuring roughly 1 centimetre across. Scientists do not believe they were made by anything walking on Mars. What has caught their attention is that the pits are different from similar depressions Curiosity has previously encountered, and their exact origin is still unclear.

Why do the Mars marks look like footprints?

Small pits and depressions are fairly common on Mars. They can develop when harder pebbles or nodules trapped inside rock gradually weather away. Once the more resistant material disappears, it can leave a hollow behind in the surrounding rock.


The newly spotted pits, however, appear to be broader and shallower than comparable formations previously observed by Curiosity. Researchers also could not identify obvious pebbles or nodules that might have once occupied the holes.

Michelle Minitti, deputy principal investigator for Curiosity’s Mars Hand Lens Imager programme, described the formations as "unlike anything we have seen in the past".


Minitti explained that while pits can form naturally when resistant material weathers out of rock, these latest examples did not fit that familiar pattern neatly.

"But 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."

The appearance may therefore be striking, but there is currently no evidence that the marks are footprints or were produced by an animal or another object moving across the surface.

Curiosity examines the unusual formations

The rover used its onboard cameras and scientific instruments to take a closer look at the area. Its Mars Hand Lens Imager, or MAHLI, and Mastcam captured overlapping images of the pits.

The images can be combined to create three-dimensional models, helping researchers examine the shape and structure of the depressions in greater detail.

The discovery could eventually provide information about the geological processes that affected this section of Mount Sharp. For now, however, scientists are still working to understand exactly how the unusual formations developed.

Minitti called them "a welcome new puzzle into the processes that have affected this particular section of rocks in the stratigraphy of Mount Sharp."

Other unusual rocks found nearby

The pits were not the only features Curiosity investigated in the area. Mastcam images and observations from the rover’s ChemCam instrument showed that nearby rock layers changed in texture and structure over relatively short distances.

Scientists believe these differences could point to changes in the conditions that existed when the sediments were originally deposited.

Curiosity also examined rough, grey-coloured layers that appeared more resistant to erosion than the surrounding bedrock. ChemCam, MAHLI and the Alpha Particle X-ray Spectrometer, or APXS, were used to analyse the material. The observations suggest that the resistant layers could have a different chemical composition from the rock around them.

Mars continues to surprise Curiosity

Curiosity landed on Mars in 2012 and has since sent back hundreds of thousands of images while examining Gale Crater and Mount Sharp. Some of its photographs have also sparked unusual claims online.

In 2013, for example, an image led some people to speculate that Curiosity had photographed something resembling a mushroom on Mars. The claim was never established as evidence of life.

For now, there is no evidence of a footprint or anything walking across the Red Planet. Instead, the tiny marks offer another opportunity to understand how Mars’ rocks have been shaped over time.