With its iconic rust tone, Mars has long been called the red planet. Now scientists may have discovered the possible source of this distinctive color, overthrowing a popular theory in the process.
Mars is one of the best studied planets in our solar system due to its proximity to Earth and the numerous spaceships that have visited it in recent decades. Together, orbiting and probes provided scientists data showing that the red color comes from oxidized iron minerals within the dust that covers the planet.
At some point, iron inside the rocks on Mars reacted with water or water and oxygen in the air, creating iron oxide – very similar to the way rust forms on earth. Over billions of years, iron oxide has decayed in dust and has settled throughout the planet after being moved by the Martian winds, which still generate swirls of dust and storms of massive dust.
Previous analyzes of Iron Oxide on Mars, based only on spaceship observations, did not detect, which led the researchers to believe that iron oxide should be hematite. It was believed that dry mineral, a main component of iron ore, had formed through reactions with the Martian atmosphere in a process that occurred over billions of years. If this were the case, the hematite would later have graduated in the history of Mars, after the planet was suspected that she housed lakes and rivers on her surface.
New research by combining data from multiple missions and replicated Martian dust suggested that a mineral who forms in the presence of cold water can be responsible for the red tone instead of hematite, which could change the way scientists understand how it was Mars of years – and if it was potentially habitable.
A team of scientists reported the findings on Tuesday (25) in the magazine.
“Mars is still the red planet,” said the main author of the study, Valantine Adomas, a postdoctoral researcher at the Earth, Environmental and Planetary Sciences Department at Brown University in a statement. “It’s just that our understanding of why Mars is red has been transformed.”
Scientists have wondered about the exact composition of iron oxide in Martian dust, because understanding how it formed would allow them to essentially look back in time to see what the environment was like and the climate on the ancient Mars.
However, even if the dust covers everything on Mars, it is difficult to study it and presents a puzzle, said Briony Horgan, co-inlaid in the mission of Rover Perseverance and professor of planetary science at Purdue University in West Lafayette, Indiana. Horgan was not involved in the study.
“The particles (of oxidized iron) are so small (nanometers or less) that they really do not have a defined crystal structure and cannot be called real minerals,” said Horgan. “There are ways to form oxidized iron without water, and some proposed dry processes include superficial oxidation such as oxidation crusts that form in rocks in the antarctic dried valleys, and superficial oxidation by abrasion as the surface is bombarded with long grains of sand by long periods. But there are also many ways to oxidize with water as well, including soils and lakes. ”
The new analysis points to a different type of iron oxide containing water called ferrihyhydritis, which form quickly in cold water – and probably graduated from Mars when water could still exist on the surface before the planet became colder and more inhospitable. Previous research has suggested ferrihydritis as a possible cause of Mars’s redness, but the new study combined laboratory methods with observational data for the first time to offer evidence.
“This article is trying to find out which little -specific crystalline iron oxide could be responsible for the red component of Mars dust, which would be useful to find out, as this could help us determine which process produced dust and when it occurred,” he said Horgan.
Valantinas and his team made use of data collected by the Mars Express orbiter of the European Space Agency and the Exomars Trace Gas Orbiter, as well as Mars Reconnaissance Orbiter of NASA and Rovers Curiosity, Pathfinder and Opportunity.
The Cassis Cassis Camera of Trace Gas Orbiter, also known as the surface image system in color and stereo, revealed the exact size and composition of Mars dust particles, allowing researchers to make their own version on Earth.
Scientists have created their own Martian dust in the laboratory using different types of iron oxide. The replica dust was processed in a specialized grinder to create grains of size equal to those of Mars, with a thickness equivalent to 1/100 of a human hair.
The team analyzed dust with x-ray machines and reflectance spectrometers, similar to the techniques used by orbiting Mars as they circulate the planet. Then scientists compared laboratory data with spacecraft data.
The Mars Express Omega Reflectance spectrometer showed that even the most dusty parts of Mars contain evidence of water -rich minerals, while cassis data indicated the presence of ferrihydritis as the best correspondence for mart dust instead of hematite, when when hematite Compared to laboratory samples, said Valantinas.
The instrument has observed Mars since April 2018, capturing high resolution images of the Martian surface, said Nicolas Thomas, professor at the Institute of Physics at the University of Bern, Switzerland, who led the team that developed the camera.
“We found that the ferrihyhydritis mixed with basalt, a volcanic rock, better corresponds to the minerals seen by spacecraft in Mars,” said Valantinas, who began his research at the University of Bern using data from Trace Gas Orbiter. “The main implication is that, as the ferrihyhydritis could only have formed when there was still water on the surface, Mars rusted earlier than we thought earlier. In addition, the ferrihyhydritis remains stable in the current conditions of Mars. ”
The mystery of the red tone of Mars persisted for thousands of years, said Valantinas.
The Romans appointed Mars in honor of their God of war because their color resembled blood, and the Egyptians called the planet “Her Desher,” which means “red,” according to the European space agency.
Discovering that the tone of Mars may be due to a rust mineral containing water such as ferrihyhydritis, as opposed to the shape without hematite, surprised the researchers, said Valantinas. But this provides intriguing clues about Mars’s geological and climate history, he added.
“Since this rust containing water covers most of the Martian surface, this suggests that liquid water in the old past of Mars may have been more widespread than previously thought,” said Valantinas. “This suggests that Mars has had an environment where liquid water was present, which is an essential prerequisite for life. Our study reveals that the formation of ferrihyhydritis in Mars required the presence of either oxygen – either from the atmosphere or other sources – and of water capable of reacting with iron. ”
The study did not focus on determining exactly when the mineral graduated. However, as the ferrihyhydritis forms in cold water, it is possible that it was created about 3 billion years ago, instead of when the planet was warmer and damp millions of years earlier.
“This was a period of intense volcanic activity on Mars that probably triggered ice and interactions between water and rock interactions, providing favorable conditions for ferrihydritis formation,” said Valantinas. “The moment coincides with a period when Mars was transition from his previous, wetter state to his current desert environment.”
It is possible that, besides being in the dust, the ferrihydritis is also in layers of Martian rock. And the best way to find out is to get real samples of rocks and dust from the red planet. Rover Perseverance has already collected multiple samples containing both, and NASA and ESA expect a complex series of missions under the Mars Sample Return program to bring them to Earth in the early 2030s.
“Once we receive these precious samples in the laboratory, we can measure exactly how much ferrihydritis the dust contains and what this means to our understanding of water history – and the possibility of life – in Mars,” said Colin Wilson, a project scientist Trace Gas Orbiter and Mars Express of ESA, in a statement.
Meanwhile, the discoveries have new mysteries for Valantines and their colleagues resolve, including the original location of the Ferihydritis before being globally distributed in Mars through dust storms and the exact chemical composition of the Mars atmosphere when the Ferihydritis graduated. Understanding when and where dust has formed it can help scientists get insights on how they evolved the atmospheres of Earth’s early planets, Horgan said.
“Ferihyhydritis is very common in soils on earth that have a lot of water through them in a short time, either because of the melting of snow or short periods of heavy rainfall in warmer climates,” he explained.
“We also saw evidence of ferrihydritis in the lake sediments in the Gale (in Mars) crater, which is being explored by Rover Curiosity. The best way to really solve this puzzle would be to bring a sample of Martian dust to our laboratories on Earth. ”
