Rose-Colored Rock From the Sahara Is a 4.1-Billion-Year-Old Piece of Mars

NASA-funded scientists led by Yang Liu of NASA's Jet Propulsion Laboratory reported Thursday in Science that Teghaza 001, a meteorite found in Mali's Sahara in 2022, is a Martian rock more than 4.1 billion years old, NASA said.

What NASA says

The rock weighs nearly 2 pounds (800 grams), according to NASA's release. It is named for the salt plain in Mali where it was found. NASA counts roughly 435 meteorites from Mars on Earth, and says this one is among the oldest.

The Science paper is an initial characterization of the rock. NASA says it gives a rare snapshot of how Mars' ancient crust formed. A separate paper in Science Advances, published in June, covered the meteorite's water content, NASA said.

The team dated the rock by finding zircon crystals in it. NASA explains that zircons hold clues to when a rock formed, and geologists use them to pin down an age. The dating showed Martian water had altered the rock around 4.1 billion years ago, which suggests it first formed even earlier, according to NASA.

"It was only after we started looking closely that we realized this meteorite is really unique," said Liu, the lead author. "One of the paper's reviewers called it a Rosetta Stone for Mars."

Here is a detail worth a second look. Liu almost skipped it. Researchers at the University of New Mexico had already matched the rock's oxygen isotopes to other Martian meteorites, and it looked like a shergottite, the most common class from Mars. Liu has seen plenty of those, NASA says. She took a look anyway and found odd textures and minerals she had not seen before.

What makes it different

NASA says Teghaza 001 is one of the three most ancient Martian meteorites found on Earth. The other two give narrower views, according to the release. ALH84001 is made almost entirely of one mineral and is similar in age. The one nicknamed "Black Beauty" formed about 2.1 billion years ago and is made of small volcanic rock fragments.

Teghaza 001 carries a mix of igneous, or volcanic, minerals. NASA says that mix tells how the crust formed from cooling magma and was later altered by water underground. Its mineralogy matches what NASA's Mars Reconnaissance Orbiter has seen in the planet's cratered southern highlands, the release says.

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

NASA's release says clues in the rock's oxygen isotopes, texture and chemistry point to a much more dynamic water cycle on early Mars.

How they dated it

Caltech coauthor Francois Tissot helped with a newer dating method. NASA describes it as in-situ rubidium-strontium dating. Older methods dissolve a whole sample. This one used a piece of the meteorite smaller than a fingernail and read single mineral grains on its surface. NASA says the method is precise and fast, and it leaves rare samples intact for later studies.

Tissot said his lab is one of very few in the world able to do this kind of dating, and the first to date such an ancient Martian meteorite. "Our hope is to pave the way for dating even more Martian meteorites, or samples returned from other planets, their moons, and asteroids," he said.

Where it came from

Nobody will ever know exactly where on Mars the rock started, NASA says. The paper does name several places that match its mineralogy and chemistry. NASA's news database carries a global map from the release that marks 13 such locations.

NASA explains how a rock gets here. An impact blasts it off the Martian surface, and it later lands on Earth. Scientists confirm a meteorite is Martian by matching its minerals and chemistry to data from NASA's Mars missions, including the Viking landers and the Curiosity and Perseverance rovers.

Context

Teghaza 001 is not the first Saharan find to add to the Mars story. In an earlier NASA release, "Black Beauty," catalogued as Northwest Africa 7034, was found in the Sahara in 2011. NASA says it weighs about 11 ounces (320 grams) and formed 2.1 billion years ago. That release also says it held about 10 times more water than other Martian meteorites of unknown origin.

What is next

Liu and her co-authors want the wider science community to dig in. NASA's release calls this year's two papers "just the start," and Liu put it this way: "We've only scratched the surface." NASA does not list specific follow-up studies or dates. What the rock can say about how water and rock interacted on ancient Mars will depend on that future work.

Stay curious.

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