“This study is the result of the complementary datasets from the fleet of international missions exploring Mars from orbit and at ground level,” says Colin Wilson, ESA’s TGO and Mars Express project scientist.

Mars Express’s analysis of the dust’s mineralogy helped show that even highly dusty regions of the planet contain water-rich minerals. And thanks to TGO’s unique orbit that allows it to see the same region under different illumination conditions and angles, the team could disentangle particle size and composition, essential for recreating the correct dust size in the lab.

Data from NASA’s Mars Reconnaissance Orbiter, together with ground-based measurements from NASA Mars rovers Curiosity, Pathfinder and Opportunity, also helped make the case for ferrihydrite.

“We eagerly await the results from upcoming missions like ESA’s Rosalind Franklin rover and the NASA-ESA Mars Sample Return, which will allow us to probe deeper into what makes Mars red,” adds Colin.

“Some of the samples already collected by NASA’s Perseverance rover and awaiting return to Earth include dust; once we get these precious samples into the lab, we’ll be able to measure exactly how much ferrihydrite the dust contains, and what this means for our understanding of the history of water – and the possibility for life – on Mars.”

For a little while longer, though, Mars’s red hue will continue to be admired and puzzled over from afar.