Each year, thousands of space rocks pierce through the Earth’s atmosphere and hit the ground as meteorites. These fragments of comets and asteroids can land anywhere but are most often spotted in open terrain, such as the deserts of Africa and the Antarctic blue ice, where a meteorite’s blackened exterior can stand out.
Still, these extraterrestrial remnants can resemble Earth rocks, and to tell the difference meteorite hunters often expose their “finds” to hand magnets, which can attract more strongly to metal-rich meteorites than to terrestrial rocks. Meteorite hunters, dealers, collectors, and curators often rely on hand magnets to verify a meteorite’s identity.
But a new MIT study finds that the same magnets used to identify a meteorite usually erase its magnetic memory. They show that exposure to a magnet can reorient a rock’s microscopic grains, undoing their original orientation and any trace of its magnetic origins.
The researchers make their case with Northwest Africa (NWA) 7034, a meteorite known in collectors’ circles as “Black Beauty” for its obsidian exterior. Multiple shards of the meteorite were first discovered in the deserts of northwest Africa, and scientists determined that the rock contained crystals that formed on Mars more than 4.4 billion years ago.