Red may well be the predominant color associated with the, er, Red Planet, but it’s purple that Perseverance keeps finding on Mars. Purple-coated rocks to be exact. And they're everywhere. 

The plucky Mars rover has found these purple rocks at almost every site it's explored in Jezero Crater so far, ranging from large rocks to tiny pebbles, and yet NASA scientists aren't quite sure what this purple coating is or how it formed.

"I don't really have a good answer for you," geochemist Ann Ollila, who presented an early analysis of the mysterious purple coating at the recent American Geophysical Union (AGU) conference, told National Geographic. 

The purple appears as both a thin, smooth coating on some rocks and paint-like splodges on others. Deciphering its chemical make-up may offer insights into Mars's ancient environment.

This isn't actually the first time purple rocks — or even green rocks, for that matter — have been found on Mars. Curiosity discovered some near the base of Mount Sharp back in 2016. At the time, NASA noted that the variation in colors on Mars rocks hints at diversity of composition, and the purple-hued pebbles had been found where Curiosity's Chemical and Mineralogy (CheMin) instrument had detected hematite, an iron oxide crystal. 

It also helped that winds and windblown sand where Curiosity was exploring kept rocks dust-free, which might otherwise obscure the rocks' color.

The purple patches spotted by Perseverance have also been typically found in less dusty areas, according to another early analysis presented at the AGU conference, this time by a team, led by Bradley Garczynski of Purdue University, who are studying the coatings using images captured by Perseverance's "eye" cams, the Mastcam-Z cameras. They also may contain types of iron oxide, their findings suggest.

However, Garczynski told NatGeo we haven't seen this type of purple rock coating before, and certainly not in the frequency Perseverance seems to be coming across them. 

Ollila's team has been using Perseverances' Supercam – which can shoot a laser at rocks to vaporize them and study the rocks' properties – to study the coating. Their early results seem to show the purple layer is softer and chemically distinct from the rock layer below, and maybe enriched in hydrogen and magnesium.

Hydrogen and iron oxide suggest water played a role in forming the purple patches. Perseverance has been exploring the Jezero Crater, a meteorite impact crater that once hosted an ancient lake, and there is plenty of evidence Mars once hosted water and was even a wet planet. However, the route Percy has been taking, and encountering these purple rocks, doesn't actually follow any lake sediments, but rather rocks that formed from cooling magma. So how these purple-hued rocks arrived at their location, and how or when they came into contact with water, remains a mystery. 

Scientists have been looking into whether rock coatings found on Mars may help preserve evidence of ancient microbial life by preventing the Sun's intense radiation from degrading organic material. So chalk this new mystery up to potentially helping us discover the answer to the age-old question of whether there ever was, or could be, life on Mars.

[H/T: National Geographic]