A pink rock found by meteorite hunters on a salt flat in Mali in 2022 has been dated to at least 4.1 billion years — making it one of the oldest Martian rocks ever found on Earth, and older than any rock on Earth itself.
It is named Tegharja 001, after the salt flat where it was picked up. There are eight fragments totalling 798.5 grams; the largest weighs 442 grams.
Why the age is extraordinary
Most Martian meteorites recovered on Earth are shergottites, and they are young — generally under 600 million years old. Tegharja 001 is roughly seven times older than that, formed within the first 400 million years of Mars's existence.
It is also chemically unlike anything studied so far, coming from a region of the Martian crust that has never been sampled. Researchers have narrowed its possible origin to 13 locations in Mars's southern highlands, and plan to compare its data against measurements from the Viking landers and the Curiosity and Perseverance rovers.
What it records
The rock is basaltic — similar to the basalts formed on Earth's ocean floors and at volcanic islands such as Iceland and Hawaii. It formed from magma that rose from the mantle and became part of the outer crust.
The important finding is what it carries with it: evidence that water altered Mars's crust at least 4.1 billion years ago. That is a direct physical record from the period when liquid water is thought to have been present, rather than an inference from orbital imagery.
Matthew Genge, associate professor of Earth and Planetary Science at Imperial College London, called it one of Mars's oldest meteorites, older than any Earth rock. The findings were published in Science.
The technique is its own story
The dating came from zircon crystals, which Yang Liu of NASA's Jet Propulsion Laboratory — who first classified the rock — described as a "time capsule" allowing precise dating of when a rock formed.
Howard Melton at Caltech developed the method used. Instead of dissolving a large portion of the sample, a laser about one-tenth the width of a human hair vaporises a tiny area.
The effect is twofold. Dating time fell from about a month to about a day. And most of the sample survives for other researchers — which matters enormously when the total material in existence is 798.5 grams and cannot be replaced.
How it got here, and what it may answer
An asteroid or comet struck Mars and threw the rock into space. Mars's relatively weak gravity made escape easy. It then orbited the Sun for millions of years before Earth's gravity pulled it in, and surface weathering suggests it lay in the desert a long time before anyone found it.
The question researchers hope it helps answer is the one that makes Mars interesting: why Earth stayed wet while Mars dried out. A rock from the exact period when both were wet is the closest thing available to evidence from the moment the two planets diverged.
