Martian meteorites provide a wealth of information about the structure of the Red Planet

Mars has a distinct structure in its mantle and crust with discernible reservoirs, and this is known from meteorites that scientists at UC San Diego’s Scripps Institution of Oceanography and their colleagues have analyzed on Earth.

Meteorites formed about 1.3 billion years ago and then ejected from Mars have been collected by scientists at sites in Antarctica and Africa in recent decades. Scripps Oceanography geologist James Day and colleagues report May 31 in the journal Scientists progress on the analyzes of the chemical compositions of these samples from the red planet.

These results are important for understanding not only how Mars formed and evolved, but also for providing accurate data that can inform recent NASA missions like Insight and Perseverance and Mars Sample Return, said Day, head of the study.

“Martian meteorites are the only physical materials we have on Mars,” Day said. “They allow us to make precise, precise measurements and then quantify the processes that occurred on Mars and near the Martian surface. They provide direct information about the composition of Mars that can support the scientific truth of the missions , such as the ongoing operations of the Perseverance rover taking place there.

Day’s team pieced together their account of the formation of Mars using meteorite samples all from the same volcano, known as nakhlites and chassignites. About 11 million years ago, a large meteor impact on Mars ripped off parts of the planet and sent the rocks into space. Some of them landed on Earth as meteorites, the first of which was discovered in 1815 in Chassigny, France, and then in 1905 in Nakhla, Egypt.

Since then, more meteorites of this type have been discovered in places like Mauritania and Antarctica. Scientists are able to identify Mars as the place of origin because these meteorites are relatively young, come from a recently active planet, have distinct compositions of the abundant element oxygen compared to Earth, and retain the composition of l The atmosphere of Mars measured on the surface by the Viking landers in the 1970s.

The team analyzed the two key meteorite types nakhlite and chassignite. Nakhlites are basaltic, similar to the lavas erupting today in Iceland and Hawaii, but they are rich in a mineral called clinopyroxene. Chassignites are almost exclusively made up of the mineral olivine. On Earth, basalts are a major component of the Earth’s crust, particularly under the oceans, while olivines are abundant in its mantle.

The same is true on Mars. The team showed that these rocks are linked together through a process known as fractional crystallization within the volcano in which they formed. Using the composition of these rocks, they also show that some of the then-molten nakhlites incorporated portions of near-surface crust that also interacted with Mars’ atmosphere.

“By determining that nakhlites and chassignites came from the same volcanic system and interacted with Martian crust altered by atmospheric interactions, we can identify a new type of rock on Mars,” Day said. “Thanks to the existing collection of Martian meteorites, all of volcanic origin, we are able to better understand the internal structure of Mars.”

The team was able to achieve this thanks to the distinctive chemical characteristics of nakhlites and chassignites, as well as compositions characteristic of other Martian meteorites. These reveal an upper crust weathered by the atmosphere down to Mars, a deeper complex crust and a mantle where plumes from the depths of Mars have penetrated to the base of the crust, while the interior of Mars, formed early in its evolution, also melted to produce distinct phenomena. types of volcanoes.

“What is remarkable is that the volcanism of Mars has incredible similarities, but also differences, to that of Earth,” Day said. “On the one hand, nakhlites and chassignites formed in a similar way to recent volcanism in places like Oahu in Hawaii. There, newly formed volcanoes put pressure on the mantle, generating tectonic forces that produce more of volcanism.”

“On the other hand, Mars’ reservoirs are extremely old, separating from each other shortly after the Red Planet formed. On Earth, plate tectonics helped remix the reservoirs over time. In this sense, Mars provides an important link between what the early Earth might have looked like and what it looks like today.

In addition to Day, Marine Paquet of Scripps Oceanography and colleagues at the University of Nevada, Las Vegas and the French National Center for Scientific Research contributed to the study.