Rare Meteorite From Mars Gives Us A View Into Its Ancient Crust
"Arthur T knackerbracket" writes:
Rare meteorite from Mars gives us a view into its ancient crust
Crater counts tell us that most of the Martian surface is more than 3 billion years old, but pieces of Mars we have on Earth tell a different story. The three main classes of Martian meteorites-shergottites, nakhlites, and chassignites-are all 2.4 billion years old or younger. Until now, only two genuinely ancient Martian meteorites were known: Allan Hills 84001, found in Antarctica, and a jumbled rock from northwest Africa nicknamed Black Beauty. Now we have a third one.
A team led by Yang Liu, a planetary scientist at NASA's Jet Propulsion Laboratory, has shown that a Martian meteorite called Teghaza 001, found in the Sahara Desert in Mali in 2022, formed at least 4.1 billion years ago. "It's very old and similar to some of the oldest rocks on Earth," Liu says.
[...] Teghaza 001 is made mostly of feldspar, a pale mineral common in the crusts of rocky planets. It has darker pyroxene crystals mixed in; according to Liu, those resemble some rocks exposed in the lunar highlands. Its crystals are rather big, up to a millimeter across, which scientists interpret as an indication it cooled down slowly. "For slow-cooled rock, they tend to have time to grow bigger," Liu said.
[...] Studies of other Martian meteorites suggest that as an early ocean of magma solidified on Mars roughly 4.5 billion years ago, the mantle separated into three to five reservoirs. Teghaza 001's source does not match any of them. "In the first few hundred million years, the Martian mantle was evolving in a way that's more complicated than we thought," Liu said.
Comparing the rock's chemistry with orbital maps, the team suggests it most likely came from the southern highlands, northwest of the giant Hellas impact basin. "No matter how many meteorite samples we have, we will always have this question: Where are they coming from on Mars?" Liu said.
Liu's study on Teghaza 001 is published in Science: https://doi.org/10.1126/science.adz5646
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