- Mars is known for its red color visible to the naked eye from Earth
- Previously, Mars' red hue was attributed to hematite, an iron-oxide mineral
- New research suggests ferrihydrite, a water-rich mineral, causes Mars' red color
Mars is famous for its red colour, which can be easily seen even with the naked eye. For centuries, humans have wondered what gives the Red Planet its distinctive hue. Earlier, scientists believed that Mars red colour came from the mineral hematite, a dry iron-oxide also found on Earth, reported BBC.
They thought that continuous oxidation and weathering of Martian rocks, under water-poor conditions during the Amazonian period starting about 3 billion years ago, could explain the red colour. Like hematite, the red colour of rust also comes from iron oxides and hydroxides.
A recent study has challenged the hematite-based explanation and proposed a new possible cause. Researchers analysed data collected from NASA's Mars Reconnaissance Orbiter, the European Space Agency's Mars Express and ExoMars, and NASA's Mars rovers.
The study revealed that another mineral, ferrihydrite, a water-rich ferric oxyhydroxide, is widely present in Martian dust and is likely also found in the rocky layers beneath the surface.
This mineral could be the primary cause of Mars' red colour. Laboratory tests on synthetic Martian mixtures of basalt and ferrihydrite showed a better match with the observed data than hematite.
Ferrihydrite requires both reactive oxygen and water to form. While these are scarce on today's cold and dry Mars, they may have been present in the planet's ancient past. On Earth, ferrihydrite quickly transforms into iron oxides such as hematite, but on Mars, researchers found that once formed, it can remain stable for almost indefinitely.
