The interplanetary space is far from empty, it is littered with dust and material dating from the creation of the solar system. The asteroids and comets, metallic and rocky objects, move at a dizzying pace around the planets and our Sun. Sometimes their orbits cross that of Earth or the Earth causing a collision, the energy released by the impact is terrifying. Meteorites and comets bombard our planet since the birth of the solar system. Although asteroids seem quietly installed on their orbits between Mars and Jupiter, they are sometimes destructive and they must likely the emergence of life on Earth. The asteroids are our closest neighbors, they are in one way or another, linked to our destiny. Those who cross our orbit are called geo cruisers. Astronomers have estimated the trajectories of asteroids likely to end millions of lives on our planet.
Apophis is a small asteroid as it 250 meters wide and could represent a threat. It is now estimated that one in 45 000 probability that the stone came crashing into the Pacific Ocean on 13 April 2036. Meteorites are the remains of asteroids falling on the surface of planets. The largest meteorite, weighing several hundred tons, returning to the atmosphere with a trajectory tilted about 45 degrees and more than 30 km/s (108 000 km/h) and did not fully consumed.
A meteorite is a stony object or ferrous extra-terrestrial small that reaches the Earth's surface. If the asteroid is the celestial body in space, the meteorite is what remains when it crashed on the surface of a planet. The fall of meteorites have marked the ground floor since the dawn of time, while most of these brands have disappeared under the impact of movements in the Earth's crust or simply are covered by vegetation, the most recent are still present on the terrestrial soil. The largest meteorite fall in the atmosphere at more than 100 000 km/h and did not fully consumed. By hitting the ground a crater is formed, as when a projectile launchers in the mud. If the meteorite is very dense it can bury themselves in the center of the impact crater, but whether it is porous, it can just as easily explode in a few miles fragments km altitude and disperse over tens of kilometers around or even explode in the atmosphere by releasing all its energy as heat. Different specimens of meteorites have been collected on six continents, including the poles. Others are left behind as Hoba, the meteorite the heaviest in the world, lost in the middle of the savanna Namibia, half buried, it weighs 66 tons. The meteorite AHNIGHITO, with a mass of 34 tones of iron fell there are about 10 000 years in Greenland. It is on display at the Museum of Natural History in New York.
But most meteorites burn and break under the pressure of the atmosphere layer, as the Peekskill meteorite that fell in 1992, which could not withstand a force of pressure of 300 atmospheres. Depending on its size and internal structure, the meteorite may or may not cross the Earth's atmosphere. The impact crater is in theory, 24 times the size of meteor craters but some can reach about thirty times this size, when the car density is very high. Some meteorites have spent on other stars before landing on our soil. Some chondrites discovered in Antarctica from the moon because they have the same composition as the rocks brought back by the Apollo missions between 1969 and 1972. The meteorites could be the cause of mass extinctions of species old. The most famous being the meteorite 10 km in diameter, which caused the disappearance of the dinosaurs. Of the Chicxulub crater in Mexico with its diameter of 200 km, still traces of what happened there 65 million years. By their origin, the internal structures of meteorites are rich in information and have great significance for scientists who study live leftovers of a distant time when the solar system was barely shaped and in which debris and dust were during accretion.
Image: The meteorite fell in 1906 Willamette Valley in Oregon, is on display at the Museum of Natural History in New York, AMNH/HAYDEN
How to recognize a meteorite?
The most striking detail of a meteorite is his weight. A meteorite or ferrous siderite, is often 2 to 3 times heavier than terrestrial rocks of similar size. The rocky or stony meteorites called lithoids are 2 times lighter than terrestrial rocks same volume. The surface of a meteorite is fairly smooth but often present lines, furrows, surface depressions and deep cavities which reflect the effects of atmospheric friction on their surface.
Image: Ferrous meteorite found in Rancho Gomelia, Mexico. It is a octahedrite composed of an alloy of nickel and iron. The acid test revealing the structure itself is clearly visible Widmanstätten (size about 14 cm). credit: D. Ball, ASU
Images of meteorites
Image: A metal meteorite photographed on the planet Mars. Credit: NASA
Image: This piece of meteorite dark and smooth, 631g and a little less than 10 cm square, was found in Australia. Her present crustal signs of a merger and is almost entirely composed of pyroxene, a typical component of lava. By its internal structure grainy and abundance of isotopes of oxygen, this fragment bears no resemblance to terrestrial and lunar rocks. Its spectral signature is in fact identical to that of the crust of the asteroid Vesta. Most fragments are exposed to the Western Australian Museum. Document copyright New England Meteoritical Services.