A 4.1-Billion-Year-Old Piece of Mars Arrived in the Sahara

"This is really our first piece of Martian crust from a part of Mars we've never had a sample of before," said Lee Saper, the paper's second author, who conducted the research as a postdoctoral scholar at JPL and is now a scientist at NASA's Ames Research Center. "It records interactions of water and rock and maybe even an imprint of the Martian atmosphere as it was losing water."

No one will ever know exactly where the meteorite originated. Still, the paper identifies 13 candidate locations on Mars that match its mineralogy and chemistry.

How did scientists date a rock from another planet?

Like all Martian meteorites, Teghaza 001 reached Earth the long way: an impact blasted it off the Red Planet's surface, and its trajectory eventually delivered it to the Sahara, where collectors spotted it against the barren landscape. Researchers verified its Martian origin by matching its mineral and chemical components to data from NASA missions, including the Viking landers and the Curiosity and Perseverance rovers.

Researchers at the University of New Mexico had already classified it as Martian using oxygen isotopes (chemical fingerprints that distinguish planetary bodies), which matched those of other Martian meteorites. The rock appeared to be a shergottite, the most common class of Martian meteorite — so common that Liu, an expert in planetary samples, nearly declined to study it.

She took a look anyway, and found odd textures and minerals she had never seen before. Among them were zircon crystals, which record how a rock formed and allow geologists to date it precisely.

Caltech coauthor Francois Tissot then applied a novel in-situ rubidium-strontium dating method (a technique that measures radioactive decay within individual mineral grains) pioneered by his team. Unlike bulk analysis, which dissolves an entire sample, the technique consumed a piece of Teghaza 001 smaller than a fingernail while delivering extreme precision, preserving rare material for future studies.

"Right now, we are one of very few labs in the world able to perform this kind of age-dating, and the first to date such an ancient Martian meteorite," Tissot said. "Our hope is to pave the way for dating even more Martian meteorites, or samples returned from other planets, their moons, and asteroids."

What comes next?

The dating results startled Liu: Martian water had altered the rock around 4.1 billion years ago, meaning it originally formed even earlier. Clues in its oxygen isotopes, texture and chemistry point to a far more dynamic water cycle on early Mars than expected.

These are preliminary findings from an initial characterization, and the authors want the wider scientific community to interrogate the sample. "We've only scratched the surface," Liu said.