A Martian meteorite is helping scientists understand the interior of the red planet

Of the more than 74,000 known meteorites—rocks that fall to Earth from asteroids or planets that collided together—only 385 or so have come from Mars.

It’s not that hard for scientists to work out that these meteorites came from Mars. Various landers and rovers have been exploring the surface of Mars for decades. Some of the earliest missions—the Viking landings—had instruments to measure the composition of the planet’s atmosphere. Scientists have shown that you can see this unique structure of the Martian atmosphere reflected in some of these meteorites.

Mars also has exceptional oxygen. Everything on earth, including humans and the air we breathe, is made up of a specific combination of three isotopes of the element oxygen: oxygen-16, oxygen-17, and oxygen-18. But Mars has a completely different makeup—it’s like a geochemical fingerprint for what’s Martian.

He Martian meteorites found on Earth provide geologists like me with clues about the composition of the red planet and its history of volcanic activity. They allow us to study Mars without sending a spacecraft 140 million miles away.

A planet of paradoxes

These Martian meteorites formed from once red-hot magma inside Mars. Once these volcanic rocks cooled and crystallized, the radioactive elements in them began to decay, acting as a radiometric clock that enables scientists to tell when they formed.

From this radiometric age we know that some Martian meteorites are 175 million years old, which is geologically – quite young. Conversely, some Martian meteorites are older, and formed near the time Mars itself formed.

These Martian meteorites tell a story of a planet that has been volcanically active throughout its history. In fact, volcanic eruptions on Mars are possible even today, although scientists have never observed such an eruption.

The rocks themselves also preserve chemical information that indicates some of the major events on Mars occurred early in Martian history. Mars formed very quickly, 4.5 billion years ago, from gas and dust that formed the early solar system. Then, very soon after formation, the interior separated into a hard rocky mineral core, mantle, and shell.

Since then, very little seems to have disturbed the Martian interior—unlike Earth, where plate tectonics have worked to stir and level the Martian deep interior. To use a food analogy, the inside of Earth is like a smoothie and Mars is like a crunchy fruit salad.

Martian volcanic remnants

Understanding how Mars went through such an early and violent adolescence, but perhaps remains volcanically active to this day, is an area of ​​interest to me. I’d like to know what the interior of Mars looks like, and how its interior structure might explain features like volcanoes on the red planet’s surface.

Once geologists began to answer questions about volcanism on Earth, we typically examine samples of lava that erupted at different places or times from the same volcano. These samples allow us to distinguish local processes specific to each volcano from planetary processes occurring on a larger scale.

Turns out we can do the same for Mars. The rather oddly named Nakhlite and Chassinite meteorites are groups of rocks from Mars that erupted from the same volcanic system about 1.3 billion years ago.

Nakhlites are basaltic rocks, similar to lavas you’d find in Iceland or Hawaii, with beautiful large crystals of a mineral known as clinopyroxene. Chasignites are rocks that are made almost entirely of the green mineral olivine—you may recognize the quality type of gems of this mineral as peridot.

Along with the much more common Shergotti, which are also basaltic rocks, and a few other types of more exotic Martian meteorites, this class of meteorites makes up all the rocks that researchers have from the Red Planet.

When studied together, the nakhlites and chassinites tell researchers a few things about Mars. First, as the molten rock that formed them flowed to the surface and eventually cooled and crystallized, some older surrounding rock melted away.

The older rock does not exist in our meteorite collection, so my team had to tease out its composition from the chemical data we obtained from the Nakhlites. From this information we found that the older rock is basaltic in composition and chemically different from other Martian meteorites. We found that it was chemically weathered by exposure to water and brine.

This older rock is quite different from the Martian crustal samples in our meteorite collection today. In fact, it looks much more like what we would expect the Martian crust to look like, based on data collected by rover missions and satellites orbiting Mars.

We know that the magmas that formed nachlite and chasignite came from a specific part of the Martian mantle. The mantle is the rocky portion between the Martian crust and the mineral core. These nachlites and chassignites come from the hard, hard upper crust of the Martian mantle, known as the mantle lithosphere, and this origin distinguishes them from the common shergotites.

Shergottis come from at least two sources on Mars. It may come from parts of the mantle just below the lithosphere, or even from deeper mantle closer to the planet’s mineral core.

Understanding how volcanoes work on Mars can inform future research questions addressed by missions on the planet. It could also help scientists understand whether the planet was ever habitable for life, or possibly in the future.

indicates habitability

Earth’s active geological processes and volcanoes are part of what makes our planet habitable. The gases emitted by volcanoes are an essential part of our atmosphere. So if Mars has similar geological processes, that could be good news for the Red Planet’s habitability.

But Mars is much smaller than Earth, and research shows that since its formation, it has been losing the chemical elements needed for a sustainable atmosphere. It seems like nothing will resemble Earth in the future.

Our next steps in understanding Mars lie in learning how basaltic shergotite meteorites form. These are diverse, rich and complex groups of rocks, ranging in age from 175 million years to 2.4 billion years or more.

Studying these meteorites in detail will help prepare the next generation of scientists to analyze rocks collected using the Perseverance rover for NASA’s upcoming Mars sample return mission.

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