Chassigny meteorite in cross-polarized light –Scripps Institution of Oceanography at UC San Diego

When a meteorite smashed into Mars eleven million years ago, pieces of the Red Planet hurtled into space—and some of them landed on Earth in the form of meteorites, depositing unparalleled evidence of the planet’s makeup.

Now, scientists at Scripps Institution of Oceanography at UC San Diego have released a report after their detailed study of the Martian meteorites collected from locations across the world, including Africa and Antarctica.

Scripps geologist James Day and his colleagues analyzed the chemical compositions of the Mars debris, saying the results are important for understanding not only how Mars formed and evolved, but also for providing precise data that can inform current NASA missions like Insight and Perseverance and the Mars Sample Return.

“Martian meteorites are the only physical materials we have available from Mars,” said Day. “They enable us to make precise measurements and then quantify processes that occurred within Mars and close to the martian surface. They provide direct information on Mars’ composition that can ground truth mission science, like the ongoing Perseverance rover operations taking place there.”

Day’s team assembled its account of the formation of Mars using the meteorite samples, called nakhlites and chassignites—which all came from the same Mars volcano and were named for the locations they were found on Earth. The first of these being discovered in 1815 in Chassigny, France and then in 1905 in Nakhla, Egypt.

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

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In the study published May 31 in the journal Science Advances, the team, which was funded by NASA, analyzed the two keystone meteorite types nakhlite and chassignite. Nakhlites are basaltic, similar to lavas erupting in Iceland and Hawaii today, but are rich in a mineral called clinopyroxene.

Chassignites are almost exclusively made of the mineral olivine. On Earth, basalts are a main component of the planet’s crust, especially under the oceans, while olivines are abundant in the mantle.

Nakhla meteorite measuring 4 centimeters across – Scripps Institution of Oceanography at UC San Diego

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

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

The team, which included colleagues from the University of Nevada Las Vegas and the French National Centre for Scientific Research, was able to do this because of the distinctive chemical characteristics of nakhlites and chassignites, which reveal an atmospherically altered upper crust on Mars, a complex deeper crust and a mantle where plumes from deep within Mars have penetrated to the base of the crust. The interior of Mars, formed early in its evolution, has also melted to produce distinct types of volcanoes.

“What’s remarkable is that Mars’ volcanism has incredible similarities, but also differences, to Earth,” said Day. “On the one hand, nakhlites and chassignites formed in similar ways to recent volcanism in places like Oahu in Hawaii. There, newly formed volcanoes press down on the mantle generating tectonic forces that produce further volcanism.”

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“On the other hand, the reservoirs in Mars are extremely ancient, separating from one another shortly after the Red planet formed. On Earth, plate tectonics has helped to remix reservoirs back together over time. In this sense, Mars provides an important link between what the early Earth may have looked like from how it looks today.”

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