The story of the red planet, it turns out, may be due for a revision. At one time, experts thought that Mars was covered with fields of rocks with iron trapped inside. Somehow or other, and over a long period, those rocks reacted to water in the air. That reaction formed rust, in much the same way it does when iron and water meet on Earth. Then, over billions of years, those rocks slowly eroded. As they broke down into dust, heavy winds spread the scarlet silty substance all around, until Mars’ entire surface was coated with it.
But a new study in Nature Communications instead says that water covered much — perhaps all — of its surface. That liquid quickly reacted to the iron in the planet’s many rocks. As the water receded, then disappeared, those rocks turned into dust, which then covered the entire planet.
"One of the most exciting aspects of this research was how it contradicted the prevailing theory about Mars' red coloration," says Adomas Valantinas, an author of the paper who participated in the study while at the University of Bern in Switzerland. He is now a research fellow at Brown University in the U.S.
Origins of the Red Color
Which version is correct has profound implications to astrophysicists — and to anyone pondering whether life could have existed on the planet. That fact that water and iron form rust — or iron oxide, chemically speaking — is not up for debate. But there are many kinds of rust, formed by different chemical processes. Knowing which reactions happened at what point of the planet’s life can provide a lot of information.
Earlier observations did not have much to work with. Images from spacecraft passing by the planet did not conclusively show any evidence of water within it. Researchers studying those images decided that the particular flavor of iron oxide must be hematite, which is formed under dry surface conditions with reactions to moisture in the planet’s atmosphere.
However, combining newer observations of the planet with some laboratory experiments led some scientists to a different conclusion. The scientists decided that the planet’s red color more closely matches that of iron oxides containing water, called ferrihydrite. That version of rust typically forms quickly in cool water. Therefore the rust must have been created when the planet still had water on its surface, they report in the new study.
Read More: Evidence of Ancient Beaches Shows Us a Mars With Large, Ice-Free Oceans
Making Mars Rust on Earth
To lend credence to that theory, some scientists decided to reproduce the watery birth version of Mars rust in an Earthbound laboratory. They essentially tried to replicate various scenarios by using different types of iron oxide.
The scientists created the lab version of Mars dust with a sophisticated grinding machine that could produce grains as small as 1/100th of a human hair. They then compared their samples to images of dust collected by spacecraft orbiting the planet.
"While scientists had long thought the reddish hue came from hematite, a waterless form of rust, our research showed it actually comes from ferrihydrite, a water-containing rusty mineral," says Valantinas.
Life on Mars
However, there is only one way to conclusively prove if the early water theory of Mars dust creation is true: the return of actual dust samples from Mars. NASA has already collected such samples, and both the European Space Agency and NASA have upcoming missions that will collect more.
“Some of the samples already collected by NASA’s Perseverance rover and awaiting return to Earth include dust; once we get these precious samples into the lab, we’ll be able to measure exactly how much ferrihydrite the dust contains, and what this means for our understanding of the history of water – and the possibility for life – on Mars,” Colin Wilson, an ESA scientist said in a press release.
Only then will we really know which Mars dust story is just so.
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
Nature Communications. Detection of ferrihydrite in Martian red dust records ancient cold and wet conditions on Mars
Before joining Discover Magazine, Paul Smaglik spent over 20 years as a science journalist, specializing in U.S. life science policy and global scientific career issues. He began his career in newspapers, but switched to scientific magazines. His work has appeared in publications including Science News, Science, Nature, and Scientific American.
