teorites are observed to fall, but most are found. They fall all over, most splashing into the ocean where recovery is unlikely. Many are found by observant people who plow up an unusual rock on their farm or hear a clang when digging in their gardens. In wet climates, fallen meteorites rot practically as soon as they fall, in some cases lasting in the dirt for only a few decades. The best place to preserve them is in dry places, either wet or dry deserts (see PSRD article: Meteorites on Ice.) These environments do not necessarily perfectly preserve these valuable rocks from the sky, but they do a much better job than do temperate and tropical climates.
There are two incredibly important search areas for desert meteorites. One is Antarctica, where national agencies manage organized searches each Antarctic summer using teams of meteorite hunters in cold-weather garb to look for promising rocks atop the ice sheet. The other area is in northwest Africa, with more free-wheeling, privately-funded search efforts. That is where NWA 7034 [ Data link from the Meteoritical Bulletin ] came from. It traveled from the desert of Morocco to the desert of New Mexico via the plains of Indiana. The meteorite's terrestrial trip began when it was found in 2011 by Aziz Habibi, a Moroccan meteorite dealer. Mr. Habibi sold it in 2011 to American meteorite collector Jay Piatek, a medical doctor who runs the Piatek Institute in Indianapolis, Indiana. Dr. Piatek has a large meteorite collection and like many collectors shares his samples with meteorite researchers. He has worked with the group at the UNM Institute of Meteoritics before. Although the rock's shiny, black fusion crust clearly showed it was a meteorite, Dr. Piatek was puzzled about what kind of meteorite it was. So was Carl Agee when he received the sample from Dr. Piatek and pondered it for a month before sawing off a slice to reveal a dark-grey almost black breccia, unlike any achondrite he had seen. Once Agee and his colleagues did a bulk analysis of a small piece of NWA 7034, which had not yet received its official, certified name from the Nomenclature Committee of the Meteoritical Society [ MetSoc link ], they realized what had been sitting on Carl Agee's shelf: a piece of Mars. Dr. Piatek generously donated a slice of the valuable (scientifically and financially) sample to the UNM Institute of Meteoritics.
|Three pieces of NWA 7034 (cube is 1 centimeter on a side). Note how dark and smooth the surfaces are, typical of the fusion crust of a fresh, unweathered meteorite. The striking dark color led Carl Agee and his colleagues to nickname the rock "Black Beauty."|
Certain chemical, mineralogical, and textural features about space rocks are so distinctive that cosmochemists can make startlingly quick decisions that a rock is asteroidal, lunar, Martian, or just some kind of Earth rock. Sometimes we can tell just looking at the sample. Other times we need to look at a thin slice of it in an optical microscope. Still other times, and to be sure, we need to determine some key chemical parameters, such as the ratio of iron (Fe) to manganese (Mn), or oxygen isotopic composition. Identifying the original home of Black Beauty required some chemistry. The ratio of Fe/Mn is useful because these two elements behave quite similarly during melting and crystallization (within some geochemical limits), so their concentration ratio reflects their ratio in the planetary body in which they formed. The diagram below shows the Mn and Fe concentrations in the mineral pyroxene in NWA 7034, compared to Martian meteorites, Earth rocks, and lunar rocks.
|Concentrations of manganese (Mn) and iron (Fe) in pyroxene crystals in NWA 7034. The units are atomic formula units, often used for minerals, which show the relative abundances of atoms of ions making up a mineral. The blue dots are data from NWA 7034; the lines show the trends for Martian meteorites (red line labeled "Mars"), Earth rocks (purple), and lunar samples (green). The dots fall along the Mars line.|
One of the most definitive measures of planet