NASA-Funded Study Details One of Oldest Mars Meteorites Ever Found

A rose-colored meteorite found in the Sahara Desert in 2022 turned out to be a piece of Mars that formed more than 4.1 billion years ago, according to NASA-funded scientists who age-dated its minerals. The nearly 2-pound (800-gram) rock, named Teghaza 001 after the salt plain in Mali where it was discovered, is one of roughly 435 Martian meteorites known to exist and ranks among the three most ancient ever found on Earth. In a paper published Thursday in Science, researchers offered an initial characterization of the meteorite, providing a rare snapshot of Mars' ancient crust and formation. A separate paper published in Science Advances in June detailed the meteorite's water content, offering a look at how water shaped the planet's early surface. Together, the studies could help answer questions about how water and rocks interacted on ancient Mars. "It was only after we started looking closely that we realized this meteorite is really unique," said Yang Liu of NASA's Jet Propulsion Laboratory in Southern California, the paper's lead author. "One of the paper's reviewers called it a Rosetta Stone for Mars." What sets Teghaza 001 apart is its texture, age, and the uniqueness of its igneous, or volcanic, minerals. Its peers among the ancient meteorites offer more limited glimpses of Martian geology: ALH84001 is similar in age but composed almost entirely of one mineral, while the meteorite nicknamed "Black Beauty" formed about 2.1 billion years ago and consists of small volcanic rock fragments. Teghaza 001 instead contains a mix of igneous minerals that records how the planet's crust formed from cooling magma before being altered by subsurface water. The meteorite's distinctive mineralogy matches observations NASA's Mars Reconnaissance Orbiter has made in the planet's cratered southern highlands. Its exact point of origin on Mars will never be known, but the paper identifies several potential locations consistent with the rock's mineralogy and chemistry. "This is really our first piece of Martian crust from a part of Mars we've never had a sample of before," said second author Lee Saper, 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." Martian meteorites share a common history: each was blasted off the Red Planet's surface by an impact and eventually landed on Earth, where collectors often find them in deserts or snowy plains. Scientists verify a meteorite as Martian by matching its mineral and chemical components to data from NASA's Mars missions, including the Viking landers and the Curiosity and Perseverance rovers. Researchers at the University of New Mexico had already identified Teghaza 001 as Martian based on its oxygen isotopes, which act as geochemical fingerprints for planetary bodies, and classified it as a shergottite, the most common class of Martian meteorite. When Liu was first asked to examine the rock, she almost declined, having seen plenty of shergottites before. But she noticed odd textures and unusual minerals, and the team found zircon crystals that can be used to precisely age-date a sample. Caltech coauthor Francois Tissot helped apply a novel in-situ rubidium-strontium dating method pioneered by his team, which analyzed single mineral grains on a piece of the meteorite smaller than a fingernail. Unlike bulk-analysis techniques that dissolve an entire sample, the method is precise, fast, and preserves rare material for future study. "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." The results showed the rock had been altered by Martian water around 4.1 billion years ago, suggesting it originally formed even earlier. Clues in the oxygen isotopes, texture, and chemistry point to a far more dynamic water cycle on early Mars. "We've only scratched the surface," Liu said.