[Rockhounds] Scientists Challenge Long-Held Theory on Why Mars Is Red

[Kreigh Tomaszewski]

The fourth planet from the Sun is famously a rusty red—but scientists now
believe we’ve been wrong about how it got its distinct hue.

The red coloration comes from iron minerals in Mars’ dust—no surprise
there. But a team of ESA and NASA scientists now think that Mars rusted
earlier in its ancient past than previously known, when liquid water was
widespread on the planet’s surface.

Iron oxide—which is now dispersed across Mars—can form under different
conditions. Scientists previously thought that the iron oxide on Mars’
surface was hematite, which likely formed through interactions with the
planet’s atmosphere when Mars’ surface was dry.

But the new analysis offers a different origin—that Mars’ distinct redness
seems to match more with the color of iron oxides that contain water, or
ferrihydrite. Ferrihydrite keeps its water signature long after the water
present during its formation disappears, and the research team detected its
signatures in the reddish dust dispersed across the planet.

https://gizmodo.com/scientists-challenge-long-held-theory-on-why-mars-is-red-2000568017