More about meteorites
We have meteorites on the Earth from two types of asteroids:
- - chondritic asteroids that did not get hot enough to melt, and
- - differentiated asteroids, or "asteroids that melted." These asteroids probably melted early in the history of the Solar System due to radioactive elements.
More about meteorites
A meteorite is a piece of rock or metal from outer space that has survived its descent through the Earth's atmosphere. Most meteorites are from the asteroid belt, which is between Mars and Jupiter. In contrast, a comet is a dirty snowball of ice and dust. Most comets orbit around the Sun and spend most of their time far away from the sun. Asteroids and comets are left over from the formation of the Solar System 4.56 billion years ago, from a cloud of gas and dust called the solar nebula. Asteroids formed between Mars and Jupiter, but comets formed farther from the sun, where ices were stable. Scientists believe that the gravitational pull of Jupiter prevented the asteroids from combining to form a planet. A few meteorites are from the Moon and Mars, and were ejected from these planets by large impact events. The meteorites from the Moon are called lunar meteorites, and those from Mars are called Martian meteorites, or sometimes they are called by the abbreviation "SNCs" named after some of the meteorite types. They are very interesting because they provide information about the composition of the Moon and Mars.
Small (dust to pea-sized) pieces of rock and metal that enter the atmosphere appear as meteors (shooting stars) and meteor showers. After floating through space, the rocks enter the Earth's atmosphere and the outsides of the rocks get very hot and melt because they are traveling over 25,000 miles per hour. Meteors can form from asteroid or comet debris. Larger pieces, which survive their descent through the atmosphere, and land on Earth, are called meteorites. Just as marshmallows get burnt on the outside, meteorites develop a black fusion crust as a result of descending through the Earth's atmosphere. Meteoroids or comets, large enough to form impact craters the size of a house or larger, are rare. Meteor crater in Arizona formed 20-50,000 years ago. The diameter of Meteor Crater is 1.2 kilometers in diameters and more than 180 meters deep.
Meteorites fall everywhere on Earth. There might even be one in your backyard! One of the best places to find meteorites is in Antarctica because they are easy to spot against the white landscape. Thousands of meteorites have been recovered from Antarctica.
Why Study Meteorites?
Meteorites provide information about the early history of the Solar System. The primitive meteorites contain clues about the composition of the solar nebula and how the Solar System formed from the solar nebula. Meteorites from the Moon and Mars provide material from those planets without a space mission.
During the early history of the Solar System, the Earth was covered with impact craters and probably looked like the Moon. Over the last few billion years, erosion and mountain building have erased most of these original craters. Because there is less erosion and mountain building on the Moon, Mars, asteroids, and other moons, these craters remain. Large impact craters known on the Earth range up to several hundred miles in diameter. During the formation of an impact crater, large amounts of rock can be melted, and some melted material, called tektites, can be thrown completely out of the atmosphere before reentering and falling back to Earth, far from the crater.