Why is Mars red? Scientists explain why

Thanks to its proximity to Earth and the dozens of spacecraft sent to it, Mars has become one of the most thoroughly studied planets in the Solar System.

Data from orbital and surface instruments had revealed that Mars' red color came from rusted iron minerals in the dust that covers the planet's surface.

But a new study has revealed that the red color on Mars may not be due to hematite, as previously thought, but to a mineral called ferrihydrite, which forms in the presence of cold water.

The study, published in the journal Nature Communications, could show that water was more common on Mars in its past, and could also provide new clues about whether the planet was habitable.

Dust layer on Mars examined

Understanding the makeup of the iron oxide coating on Mars could help scientists reconstruct the planet’s past climate and environment, but the dust layer is notoriously difficult to study.

In the new research, scientists used data from the European Space Agency's (ESA) Mars Express and ExoMars Trace Gas Orbiter missions, as well as NASA's Mars Reconnaissance Orbiter and rovers Curiosity, Pathfinder and Opportunity.

The Trace Gas Orbiter's CaSSIS imaging system determined the size and composition of dust particles on Mars.

The researchers then studied different types of iron oxides by simulating Martian dust in a laboratory setting. A mixture of ferrihydrite and basalt was identified as the composition that best matched Martian dust.

Mars' history could be rewritten

Adomas Valantinas, a member of the research team, stated that the findings provide important information about the past of Mars.

“Mars is still a red planet, but our understanding of why it is red has changed,” said Valantinas, adding that ferrihydrite can only form in the presence of water , suggesting that Mars rusted much earlier than previously thought.

These findings suggest that water-bearing mineral layers are widespread on Mars' surface. It is stated that Mars experienced intense volcanic activity about 3 billion years ago, and that this process may have melted the ice and triggered water-rock interactions.

In the future, samples of rocks and dust from the planet, brought back as part of NASA and ESA’s joint Mars Sample Return Program, could provide more precise data on Mars’ water history. By analyzing these samples, scientists hope to better understand how Mars’ atmosphere and water cycle worked in the past.