Mars is known for its reddish hue , so much so that one way to refer to it is by calling it the “red planet.” This is no accident, of course. Mars shines an intense red color in the night sky and the images of the probes and rovers that we have sent there show us that same picture: a planet completely covered by a reddish or orange tint. Some areas may have a grayish or brownish hue, but the dominant color is definitely rust red . However, the Martian surface has more hues to offer us, as recently discovered by photographs taken by the Perseverance rover.
A red landscape is what we expected to find when Perseverance touched down in Jezero Crater back in February 2021. This crater was chosen as the rover’s landing point because it contained an ancient lake of liquid water within its towering walls. However, this lake inhabited Mars when the planet had oceans, a thicker atmosphere, and a magnetic field , elements that disappeared billions of years ago. At present, only the channels that the water sculpted with its passage remain, the deltas that this water formed by transporting large amounts of sediment and the rocks that formed when they settled . Well, that and the green rocks that we have just discovered, which although they are found in this same crater, do not have a sedimentary origin.
These rocks are of volcanic origin , specifically they are formed by grains of olivine , like those that abound in the geology of Lanzarote. This rock, properly polished and prepared, shines with an intense green color, which caused it to be confused many times with the emerald on this island. It is composed of silicates of magnesium and iron and is formed after the rapid cooling of lava. However, the rocks that can be found on our planet look different from those that can be found on Mars.
The olivine found on Mars is rock that formed about 4 billion years ago . Rocks that old exist on Earth, but it is very difficult to find them intact, on the one hand because plate tectonics is responsible for renewing the earth’s crust slowly but tirelessly and on the other because the rocks that have survived near the surface have suffered erosion due to wind, water and , more recently geologically speaking, life itself . On Mars, however, plate tectonics ground to a halt early in its existence, a few hundred million years after the solar system formed, and erosion has been much more restrained. This makes Martian rocks much easier to analyze and study .
Studying these rocks and understanding their evolution over time will allow us to understand how the geology and climatology of Mars have changed . This can give us information about whether Mars had optimal conditions for life in the past, and even shed light on what conditions on Earth might have been like when life arose. In fact, part of what makes it difficult to know the conditions in which life evolved on our planet is precisely that the rocks that covered our planet at that time have largely disappeared . Martian rocks, however, have been preserved without much change since they were formed, so they can be a perfect laboratory to study the origins of the solar system.
On the other hand, understanding under what conditions terrestrial life arose can make it easier for us to search for extraterrestrial life on other planets or moons in our solar system. The search for present or, more likely, past Martian life is one of the main goals of the Perseverance rover .
The olivine rocks found by the rover do not share the reddish hue of the rest of the planet’s surface because of how they were formed and because of their chemical composition and crystal structure. The red of Mars comes from a process that we know very well on our planet: it is iron oxide or, as it may sound more familiar to you, oxidized iron. The same process that spoils our iron tools and materials and gives them the characteristic reddish hue of this chemical reaction has given the red planet its color. A piece of iron, especially after being wet, will rust just by being in contact with the oxygen in the atmosphere . Something similar has happened on Mars. It happened in the past, when the planet contained water, and it continues to happen in the present, on geological timescales.
All of these discoveries, made with the limited instrumentation that can be loaded onto a rover the size of a small car, underscore the need to send specialized astronauts to Mars who are capable of conducting deeper and more detailed investigations of everything let’s find
Roger C. Wiens et al, 2022, Compositionally and density stratified igneous terrain in Jezero crater, Mars. Science Advances, DOI: 10.1126/sciadv.abo3399
Y. Liu et al, 2022, An olivine cumulate outcrop on the floor of Jezero crater, Mars. Science, DOI: 10.1126/science.abo2756
K. A. Farley et al, 2022, Aqueously altered igneous rocks sampled on the floor of Jezero crater, Mars. Science, DOI: 10.1126/science.abo2196