The reddish color of Mars is perceived with the naked eye. Perhaps by association of red with the blood, the Babylonians will link him with Nergal, his god of war, something that the Greeks and Romans also did by calling him Ares and Mars. As for why it is a red planet, we have news.
Mars is oxidized. For a long time it has been known that the characteristic reddish tone of Mars is due to the presence of iron oxides in the dust on its surface.
A new international study that combines data from the European Space Agency (ESA) and NASA with laboratory experiments suggests that these iron oxides were formed in the presence of water long before what was believed.
A surprisingly wet story. Until recently, it was thought that the predominant iron oxide in Mars was hematite, a mineral that can be formed with little or no presence of liquid water on the surface, provided there is an oxidizing agent in the atmosphere.
However, the new observations and laboratory analysis show clear indications of water in the spectral firm of the Martian dust. This finding indicates that ferrihydrite, an iron oxide with water molecules integrated in its structure, is responsible for the unmistakable red color of the planet, showing that Mars has a more humid story of the established.
What is ferrihydrite and why it matters. Ferrihydrite is a badly crystallized and iron ore that is rapidly formed in the presence of fresh water and with moderate oxidation levels.
Its structure retains water molecules or other hydroxyl groups inside, so that it leaves a water footprint even under drier subsequent conditions. This feature contrasts with the hematite, which is anhydra and much more stable when there is no liquid water around. Therefore, Ferrihydrite’s discovery implies that in the past of Mars there were episodes with relatively abundant liquid water.
The methodology. To reach this conclusion, the researchers combined measurements of several probes and rovers of the ESA (Mars Express and the Trace Gas Orbiter) and NASA (Mars Reconnaissance Orbiter, Curiosity, Opportunity and Pathfinder) with laboratory experiments.
These experiments consisted of creating simulated Martian dust mixing ferrihydrite with ground basalt in particles a hundred times finer than a human hair. Then, they measured the optical properties of these samples in the same way that the instruments on Mars do, confirming that the ferriidrite explained better the spectral firms of the red planet.
A red planet with secrets to reveal. On Earth, ferrihydrite is usually transformed over time into more crystalline phases (such as Goetita or Hematite) if the temperature and water availability conditions allow it. Mars is extremely cold, dry and exposed to a very little dense atmosphere. These conditions hinder the transformation and favor that the ferrihydrite is kept as is, retaining its “water seal” despite the billions of years after it was formed.
The image of Mars as an arid and reddish planet has not changed with this study, but our understanding of its past yes. The confirmation of an oxidation phase in the presence of water indicates that the planet had more humid periods and with the possibility of hosting living organisms.
Image | ESA/DLR/FU BERLIN/G. Michael, A. Valantines
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