A space odyssey, or, how a little piece of the planet Mars ended up on a shelf in my bedroom.
My own little piece of Mars---a fragment of Mars Meteorite NWA 2975.
In November 2005, a meteorite collector and dealer named Mike Farmer was approached by a supplier in Morocco with a meteorite for sale. Morocco is famous as a gateway for the sale of meteorites that are found throughout the vast Sahara area by nomadic Berber tribesmen, who collect and sell them as a side income. As anyone who has watched "Meteorite Men" on TV knows, deserts are perfect areas for hunting meteorites, since the bare sand makes it easy to spot them on the surface, and the dry conditions help preserve them.
Farmer learned that this particular meteorite, which he purchased and then officially cataloged with the International Society for Meteoritics and Planetary Science as NWA 2975 (the 2,975th meteorite listed from North West Africa), had been found in Algeria earlier that year. Algeria has long been a rich area for collecting meteorites--about 700 different meteorite sites have been discovered there over the years. Farmer's original piece of NWA 2975 weighed about 70 grams, but over the following years, additional pieces of the same meteorite were found in a scattered "strewn field", where they landed after breaking up in the atmosphere. By 2012, about 3.5 pounds of this meteorite fall, in 102 fragments of varying size, had been collected and sold through markets in Morocco to various dealers and collectors. The additional fragments were "paired" with NWA 2975, and the largest fragments were cataloged as NWA 2986, 2987, 4766, 4783, 4857, 4864, 4878, 4880, 4930, 5140, 5214, 5219 and 5366. Smaller uncataloged pieces are referred to under the NWA 2975 label. All are from the same meteorite fall.
At first, there was nothing special about NWA 2975 and its sister fragments. Then, in 2006, the "Meteoritical Bulletin" (the official clearinghouse for global meteorite finds) published the results of lab tests on the meteorite, and those results came as a surprise . . .
In 1979, a meteorite cataloged as EETA 79001 had been found in Antarctica. Weighing in at about 17.5 pounds, it was determined to belong to a rare class of stony meteorites which shared a unique mineral composition, known as "basaltic shergottites". The name came from the village of Shergotty, India, where the first of these meteorites had been found back in 1865. When EETA 79001 was examined and radio-dated, it was found to be unusually young. Nearly all meteorites come from asteroids that formed from the same condensed stellar cloud as the planets, and all of these date to about 4.5 billion years old, but EETA 79001 was only 1.3 billion years old, and the other shergottite meteorites were also much younger than the asteroids. They must have come from something else. Scientists were puzzled.
The mystery remained until 1983, when it was discovered that the tiny air bubbles trapped inside EETA 79001's glassy interior contained small samples of an atmosphere that did not correspond to Earth. When geologists compared these gas bubbles with data from the 1976 Viking lander on the chemical composition of the atmosphere on Mars, they found a perfect match. The conclusion was unmistakable---the "basaltic shergottite" meteorites were rocks from Mars.
And when planetary geologists examined NWA 2975 in 2006, they found that it too was a basaltic shergottite, with tiny bubbles of Martian atmosphere. It, and its 101 additional fragments, were rocks from Mars. Like the other shergottites, NWA 2975 also contained large crystals of maskylenite, formed when the rock melted under an enormous shock and then recrystalized. At some point in its past, it had been subjected to a tremendous impact.
So how does a piece of Mars rock end up in Algeria on Earth? About 1.1 million years ago, Mars was hit by a large asteroid. The impact was strong enough to hurl pieces of molten Mars rock at escape velocity (Mars, with its much lower mass, has a lower escape velocity than Earth does), sending them into space, where they went into orbit around the sun. After perhaps a million years, one of these orbiting chunks of Mars rock became caught in Earth's gravitational field, where it was pulled in, broke up on entry, and landed as a meteorite shower in Algeria, to be found in 2005. Because NWA 2975 was not observed as it fell, it is unknown how long the fragments were lying on the surface of the Algerian desert before being discovered by a wandering Berber.
Mars meteorites are, of course, enormously rare. Only 68 different Mars meteorites (many of them fragmented) are known so far, including the celebrated ALH 84001 found in Antarctica in 1984, which was asserted to contain fossilized remains and chemical signatures of Martian bacteria. Although a number of landers and rovers have explored the surface of Mars over the past 50 years, none of them have returned any rock samples to Earth. The Martian meteorites are therefore the only actual pieces of Mars available for planetary geologists here on Earth to study.
Of the 102 fragments of NWA 2975 that have been recovered so far, a number were distributed to space researchers around the world for investigation. The air bubbles and the large crystals of maskylenite make them invaluable to scientists; the air bubbles provide tiny samples of Martian atmosphere, while the maskylenite crystals trap radio-decay products like argon and allow the samples to be radio-dated.
The remaining fragments were released for sale to collectors, and have become available through a number of different commercial meteorite dealers. My fragment, weighing 1.272 grams and about the size of a raisin, came from a meteorite dealer in Alaska. Pieces of NWA 2975 typically sell for between $500 and $1,000 per gram, depending on the quality of the piece and the completeness of its outer fusion crust.
Shortly after obtaining my piece of Mars, I contacted the Museum of Science and Industry in Tampa, and offered to loan it to the museum for display. They declined, stating that producing a secure display case for the fragment would be too expensive for them. So now the Mars meteorite piece sits on a shelf in my bedroom, next to my collection of fossils and Stone Age tools.