Martian Fossils On Earth: The Story of Meteorite ALH 84001
The rock is known as meteorite ALH 84001 It is about the size and shape of a potato and weighs 1 94 kilograms about 4 pounds A meteorite is a rock that fell to Earth from space Meteorite ALH 84001 landed in the Allan Hills area of Antarctica about 13,000 years ago It was discovered discovered in December 1984 by the scientists of the Antarctic Search for Meteorites ANSMET project originally led by William A Cassidy and now led by Ralph P Harvey ANSMET scientists have found about more than 20,000 meteorites since the project began in 1976 After each meteorite hunting season the ANSMET scientists send their extraterrestrial rock collection to the Lyndon B Johnson Space Center JSC in Houston Houston Texas There the meteorites are numbered and
carefully cut into pieces which are sent to scientists all over the world for study ALH 84001 was the most interesting and unusual item in the Allan Hills 1984 1985 rock collection The meteorite’s name means Allan Hills 1984 1985 season number 001 Some meteorites come from wandering chunks of rock left over from the formation of Earth and other planets of the solar system Other meteorites appear to be fragments of Moon sized bodies that formed and then were broken apart Like the planets meteorites meteorites travel at very high speeds around the sun in paths called orbits If a rock’s orbit brings it near Earth it may enter Earth’s atmosphere and collide with our planet Just as water slows your body when you dive into a swimming pool the atmosphere slows the rock Scientists Scientists call the force that slows your body or the rock friction The friction transforms the rock’s energy of motion into heat The rock begins to melt and the atmosphere begins to glow forming a streak of light that crosses the sky When we on Earth see the glow we call it a meteor or a shooting star although it has nothing to do with stars Most meteors are small or are made of light
materials These burn up entirely when they enter the atmosphere leaving only vapor and bits of dust A few meteor causing bodies are large and fall to the ground as meteorites How do scientists recognize a meteorite First the outside of a meteorite shows signs of its fiery trip through the atmosphere It is often oddly shaped and its surface is smooth or glassy Second the rock is out of place It is made of minerals unlike the other rocks around it Sometimes the original meteorite is so huge that it leaves a visible crater on Earth About 10,000 years ago a large rock composed mainly of iron and nickel struck the ground about 50 kilometers 30 miles east
of the present day city of Flagstaff Arizona It blasted out a huge hole about 1 kilometer more than half a mile across It is commonly called Meteor Crater although its official name is the Barringer Meteorite Crater Many nickel iron meteorites have been col lected from that site Scientists classify each meteorite as a member of a family according to its physical appearance and mineral makeup A meteorite family is often named after the location where the first such meteorite is found ALH 84001 is a shergottite meteorite The first known shergottite meteorite fell in Shergotty India on August 25 1865 ANSMET scientists have since found many more shergottite meteorites including the small black crusty one pictured here designated QUE 94201 It was found in the Queen Alexandra Range during the Antarctic summer of 1994 1995 A meteorite that fell and killed an unfortunate dog in Nakhla Egypt on June 28 1911 was the first to be classified as nakhlite Another fell in Chassigny
