Sahara meteorite Teghaza 001 is a Martian rock at least 4.1 billion years old

A fragment from the Sahara

Teghaza 001 was found in September 2022 in the Sahara, in Mali, about 34 kilometres from the locality of Bir Chali. It came as eight fragments, the largest roughly the size of a fist, weighing just under 800 grams in total. The stones entered science through the desert meteorite trade, in which hunters search the sand for dark rocks that stand out. A private collector bought them and sent a piece to the University of New Mexico, where Carl Agee and Karen Ziegler measured its oxygen isotopes. The values matched those of other Martian meteorites, but the rock was first classified as a shergottite, the most common and youngest class, until Agee noticed oddities and contacted Yang Liu at NASA's Jet Propulsion Laboratory.

Why ancient Martian rock is scarce

Crater counts suggest most of Mars' surface is over 3 billion years old, yet all three main classes of Martian meteorites are 2.4 billion years old or younger. Before this study only two genuinely ancient Martian meteorites were known: Allan Hills 84001, found in Antarctica, and Black Beauty, a jumbled rock from northwest Africa. Liu's explanation starts with how material leaves the planet. A large impact is needed to launch a rock off Mars, and weakly bound material may not survive that launch.

“If the impact hits into loose powder, it may not get cemented to become a rock and fly off Mars' gravity.”

That filter leaves scientists with a biased collection. Black Beauty is the partial exception, since its chemistry matches orbital measurements, but it is a mix of soil and small fragments. Teghaza 001 is a single intact igneous rock, and Liu says it is very old and similar to some of the oldest rocks on Earth.

Teghaza 001 (at least)4.1

Three main classes (up to)2.4

Teghaza 001 (at least)

4.1 billion years

Three main classes (up to)

2.4 billion years

Data from the article text

What the rock records about Mars

Teghaza 001 is a gabbro, a coarse-grained igneous rock made mainly of feldspar and pyroxene, with zircon crystals that contain uranium. Researchers dated it through uranium-to-lead decay, which gave an age of at least 4.1 billion years. The magma that formed it came from deep in the Martian mantle and cooled slowly underground, while water interacted with the rock. Isotopes of oxygen and hydrogen indicate that surface water seeped into deeper crust and mixed with molten rock, a process resembling one on Earth. Only three known meteorites come from this early stage of Mars, and the new work concludes that Teghaza 001 is probably the oldest of them. Liu describes the rock as a witness to a time when Mars was probably warmer and wetter than for most of its history.

Limits and open questions

Lee Saper, a researcher at NASA Ames Research Center and co-author of the study, said the results support conditions favorable to microbial life on early Mars. The findings do not prove that organisms ever existed there. Researchers also say Mars likely began with a denser atmosphere and a wetter environment, and that these conditions deteriorated gradually during its first billion years. Researchers suspect Teghaza 001 may have come from high terrain in the southern hemisphere, possibly near the Hellas basin. Researchers do not know exactly when the rock reached Earth.