On 1994 July 16-22, over twenty fragments of comet Shoemaker-Levy 9 collided with the planet Jupiter. The comet, discovered the previous year by astronomers Carolyn and Eugene Shoemaker and David Levy, was observed by astronomers at hundreds of observatories around the world as it crashed into Jupiter's southern hemisphere. This past July, a comet or asteroid ripped another Pacific-Ocean sized hole in Jupiter. Is Jupiter a giant protective magnet for Earth, or are these events wake-up calls?As Stephen Hawking says, the general consensus is that any comet or asteroid greater than 20 kilometers in diameter that strikes the Earth will result in the complete annihilation of complex life - animals and higher plants. (The asteroid Vesta, for example, one of the destinations of the Dawn Mission, is the size of Arizona). Since 1941 many astronomers have thought of Jupiter as a protective big brother for planet Earth -a celestial shield, deflecting asteroids and comets away from the inner Solar System. This long-standing belief that Jupiter acts as a celestial shield, deflecting asteroids and comets away from the inner Solar System, has been challenged by the first in a series of studies evaluating the impact risk to the Earth posed by different groups of object ... read more ...