For decades, scientists have assumed that the red color of Martian dust came from iron oxide, or rust, similar to what is found on Earth. However, a new study published in Nature Communications suggests that the mineral responsible for the reddish hue is actually ferrihydrite, a type of iron oxide that forms in cold, dry environments.
The discovery was made by Adomas Valantinas, a doctoral student at Brown University, who led the research and compared laboratory data with spectra from spacecraft. Valantinas found that Martian dust most closely resembles ferrihydrite, which contains water, iron, and oxygen. On Earth, this mineral typically forms in cool, moist environments but can change into other forms of iron oxide when it’s warmer or drier.
Valantinas conducted experiments using a simulated Mars analog environment to test how ferrihydrite would weather the Martian environment. The results showed that ferrihydrite lost some water but remained essentially frozen and stable at temperatures averaging -70°C (-94°F). A kinetic model suggested that at Mars-like temperatures, the compound would persist for billions of years.
The researchers believe that ferrihydrite might have formed during an oxidative spell on early Mars when liquid water and oxygen became available. The compound was then preserved even after the loss of liquid water as the Martian climate cooled to its current dry and cold state.
While this discovery resolves a long-standing puzzle, more research is needed to fully understand the origin of the iron oxide in Martian dust. Valantinas plans to survey Mars more thoroughly to determine if the iron oxide came from localized formations that were then scattered across the planet by windstorms.
Source: https://skyandtelescope.org/astronomy-news/why-is-mars-red