Baku, February 27, AZERTAC

Everyone knows Mars is the “red planet,” but a new study is reshaping scientists’ understanding of why the planet has its distinctive hue — and it could also reveal a wetter, potentially habitable Martian past, according to Forbes.

Mars’s surface is covered in a fine layer of iron oxide dust, which has been spread across the planet by wind over billions of years. However, whether that rust was initially produced in dry or wet conditions was unclear.

Using data from spacecraft at Mars and laboratory work, the study discovered that the planet's red color comes from ferrihydrite, a water-rich iron oxide. Although it's long been known this red color is due to rusted iron minerals in the dust, it was previously thought to be caused by hematite, an iron oxide mineral that's the main component of iron ore, which was believed to have formed on a dry planet.

The discovery brings planetary scientists one step closer to uncovering the planet’s watery past — and the possibility that it once supported life.

This discovery of the exact chemistry of Martian rust changes that theory. Ferrihydrite typically forms in water, so it must have formed when Mars still had water on its surface.

"The major implication is that because ferrihydrite could only have formed when water was still present on the surface, Mars rusted earlier than we previously thought," said Adomas Valantinas, lead author on a paper published this week in Nature Communications. "Moreover, the ferrihydrite remains stable under present-day conditions on Mars.”

The researchers found that ferrihydrite mixed with basalt, a volcanic rock, best fits the minerals seen by spacecraft on Mars. “Mars is still the Red Planet," said Valantinas, a postdoc at Brown University in Rhode Island, formerly at the University of Bern in Switzerland where he started his work. “It’s just that our understanding of why Mars is red has been transformed.”

This finding challenges previous assumptions that Mars’ surface has been dry for billions of years. Instead, it suggests that water played a role in the planet’s rusting process much earlier than expected.

The research team used a combination of data from multiple Mars missions, including the European Space Agency’s Trace Gas Orbiter and Mars Express, as well as NASA’s Mars Reconnaissance Orbiter.

“We eagerly await the results from upcoming missions like ESA’s Rosalind Franklin rover and the NASA-ESA Mars Sample Return,” said Colin Wilson, project scientist on ESA’s TGO and Mars Express missions. “Once we get Martian dust samples into the lab, we’ll be able to measure exactly how much ferrihydrite is present and what that means for Mars’s history.”