Harbour Jingxian cosmic dust.

<P> Technology Channel (tech.) Message: traffic accidents in the universe? .</ P> <P> about 800 million years ago, a terrible place in the solar system's asteroid collision, according to today's Veritas asteroid family that is born from the collision. .Geochemists have recently said they were found in bottom sediments of evidence of the accident - spilled after the collision of cosmic dust to Earth. .</ P> <P> planets in the solar system have their fixed orbit, some are wandering asteroids and comets, may collide with each other, or hit the planet. .Many scientists believe it is an asteroid hit the Earth, resulting in the extinction of the dinosaurs. .Sometimes, the Earth is not such a collision, "the parties", but the collision of debris and dust will fall to Earth. .</ P> <P> California Institute of Technology geochemist Kenneth Farley and others in the UK "Nature" magazine reported that they found in a layer of sediments rich in cosmic particle deposition, indicating that had occurred .once a large amount of cosmic dust collision. .</ P> <P> scientists to determine the basis for this is a special kind of sediment in the isotope helium - helium-3 content. .Helium-3 contains two protons and one neutron, is extremely rare on Earth. .Dust particles in interstellar space travel a long process, will absorb more of the helium-3. .</ P> <P> by analyzing the content of helium-3, Farley, who found that at 820 million years ago, floating down to Earth cosmic dust suddenly increased to 4 times the usual number, which is in the past 100 million years, the highest value .one. .Then, gradually reduce the amount of dust landing, about 150 million years after the return to near normal levels. .Thesis partner, Southwest Research Institute David Nesvorny home made planetary dynamics, the asteroid's destruction with a larger time line, this incident led to the birth of the Veritas asteroid family. .</ P> <P> Veritas asteroid family is a group inside the asteroid belt objects, about 300 members, of which the largest diameter of 115 km, orbits similar to each other (Veritas Roman mythology, the goddess of wisdom) .. .Nesvorny of the orbital evolution of their proposed after, these asteroids were all born in about 800 million years ago an impact event, when an asteroid 150 km in diameter with a smaller celestial body collided with 18,000 km per hour .. .</ P> </ p>.