Scientists have identified one of the oldest Martian rocks ever discovered on Earth, offering new evidence about the red planet’s earliest history. The meteorite indicates that water altered the Martian crust at least 4.1 billion years ago.

Known as Teghaza 001, the rose colored specimen has a chemical composition unlike previously studied samples from Mars. Scientists say its distinctive chemistry provides access to a region of the planet’s crust that had not been sampled before.

The findings appeared October 29 in the journal Science, with NASA Jet Propulsion Laboratory planetary scientist Yang Liu serving as the study’s lead author. “This is a very rare, ancient Martian meteorite, and it gives us a chance to look at the early crust and mantle of Mars, at a time when life was just starting on Earth,” Liu said.

Researchers believe the meteorite formed from magma derived from the mantle, a planet’s inner layer of hot rock, before becoming part of the outer crust. “The chemistry of this sample shows it comes from a Martian crustal area we have not sampled before,” Liu added.

Teghaza 001 was named after a salt plain in Mali, the West African country where meteorite hunters found it in 2022. Its eight fragments weigh 798.5 grams, or 1.76 pounds, in total, while the largest fragment weighs 442 grams, or 0.97 pounds.

An asteroid or comet impact blasted the rock away from Mars and into space. The resulting meteoroid may have orbited the sun for several million years before Earth’s gravity captured it and it entered the atmosphere.

Researchers cannot determine when the impact on Mars happened or when the meteorite reached Earth. However, surface features suggest that the specimen might have remained in the desert for some time before its discovery, according to Liu.

Matthew Genge, an associate professor of Earth and planetary science at Imperial College London who was not involved in the research, called it a fascinating window into early Martian history. “It is always nice to see a new visitor from Mars, and this one is ancient — one of the oldest from the planet, and older than any home-grown Earth rock,” he said.

The rock’s significance was not immediately apparent, and Liu nearly passed on studying it after it was initially classified as a shergottite. Such rocks represent almost 90% of the known Martian meteorite collection and are generally less than 600 million years old.

Liu ultimately investigated Teghaza 001 and discovered that it contained zircon, a crystal that forms as molten rock cools. “Zircons are like a time capsule that allows us to precisely date the formation age of a rock,” she said.

Dating those crystals produced an age of at least 4.1 billion years, placing the rock’s formation within roughly the first 400 million years of Mars’s existence. The researchers confirmed that estimate using a new aging method developed by study coauthor Hayward Melton, a doctoral student at the California Institute of Technology.

The method uses a laser to vaporize extremely small areas of a sample rather than dissolving larger pieces. Researchers directed a beam about one tenth the diameter of a human hair at tiny grains and crystals within the meteorite.

According to Melton, the technique reduced the time required to date a sample from a month to a day. It also preserved more of the meteorite’s original material for additional research.

Teghaza 001 is a basalt, similar to rocks found across the floors of Earth’s oceans and erupted by volcanoes in Iceland and Hawaii, Genge said. Its composition shows that it interacted with water in the ancient Martian crust.

The meteorite consists mainly of two minerals rich in calcium, arranged in proportions not previously observed in other samples, Liu said. It also contains oxygen isotopes in a relative abundance unlike that found in other known Martian rocks.

Scientists compared the specimen’s mineral and chemical composition with information gathered by NASA’s Viking landers and its Curiosity and Perseverance rovers. They identified 13 locations in Mars’s southern highlands where the meteorite might have originated.

Meteorite collector Darryl Pitt, chair of the meteorite division at the Maine Mineral & Gem Museum in Bethel, Maine, became interested in Teghaza 001 after its discovery. Pitt later brokered an agreement for the museum to acquire the rock for an undisclosed amount.

Liu expects the scientific community to remain interested in the meteorite as researchers continue investigating unanswered questions. “I am still very interested in resolving some questions I couldn’t answer with our paper, which is only in the beginning,” she said.