A meteorite from Mars is a rare bird indeed. There are only about 60 known. A witnessed fall of a Martian meteorite is rarer still. The last time it happened was on October 3, 1962 in Nigeria when the 40 lb. Zagami meteorite landed about 10 feet away from a farmer who was chasing cows from his field. Fifty years later another piece of Mars came zinging through the sky, this time in Morocco.
At about 2 a.m. local time July 18, 2011 nomads and military personnel south of Tata, Morocco were awakened by sonic booms and a bright light from a large fireball. One eyewitness reported that the meteor turned from yellow to green and split into two pieces. Three months later in October, nomads found fresh, black fusion-crusted stones about 30 miles south of the village of Tissint. French meteorite hunter Luc Labenne was guided to the site of the fall by local meteorite hunters. He gathered up several samples and sent two grams worth for testing to Brigitte Zanda and Violaine Sauter at the National Museum of Natural History in Paris. They determined the crust was very fragile and fresh, good indications that it fell recently. Labenne then sent more pieces to an American researcher who confirmed their Martian origin.
The meteorite was officially named Tissint this week by the Meteoritical Society, but you might still see earlier references to its informal names Tata, Tanzrou and Foumzgit on some online sites. Either in the air or when it hit the ground (probably both), the new space rock shattered into many small fragments with weights ranging from about one gram to 987 grams. Few complete stones were found in the approximately 7 kilograms or 15.4 lbs recovered. The interior is pale gray dotted with occasional olivine crystals. As you might expect, the discovery and sale of pieces have been hot topics in both the meteorite collecting community and among scientists eager to study one of the freshest Mars rocks they’ll ever get their hands on.
Tissint is an igneous rock called a shergottite, named after the Shergotty meteorite that fell in India in 1865. Shergottites crystallized from hot magmas on Mars between 150 to 500 million years ago and were later ejected into space by large meteorite impacts. Their most likely sources are the young volcanic regions of Mars like the vast Tharsis Plateau, home to Olympus Mons, the biggest volcano in the solar system.
Most meteorites are 4.5 billion years old and date from the earliest days of the solar system, when asteroids were colliding and coalescing to form the planets. So while shergottites’ ages sound old, they’re very young by planetary standards and could only have formed relatively recently on a volcanically active planet other than Earth. That plus their particular chemical makeup and the trapped gases they contain that match those measured by the Viking and and other Mars landers clinch their Martian connection. Shergottites come in several varieties; ones rich in pretty green olivine like this one are classified as olivine-phyric types.
You might think meteorites from Mars would be red – or god forbid, green – based on the planet’s overall color, but they’re far more drab. The red is iron oxide dust blown by Martian winds across the planet. It coats everything, but the rocks themselves are gray, mostly volcanic rocks.
Dr. Carl Agee, director of the Institute of Meteoritics at the University of New Mexico in Albuquerque, describes glassy melt pockets in Tissint, perfect for holding trapped gases and other Martian morsels. Melt, a sign of heating from impact and shock, will help tell us the story of the meteorite’s past – its catastrophic excavation, long journey through space and fiery delivery to Earth.
Best of all, a freshly-fallen stone has minimal weathering. This is truly pristine material. Whatever researchers find when they drill deep inside the new Tissint meteorite, whether that be signs of water or organic compounds, it’ll be the real deal from Mars, not contamination from Earth’s sticky hands.