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An asteroid the size of a truck zoomed near Earth this week (June 1), coming closer to us than the moon ever does. The 23-foot-long (7-meter) space rock, named 2009 BD, came within 215,000 miles (346,000 kilometers) of Earth at around 8:51 p.m. EDT (0051 GMT on June 2). The moon's average distance from us is about 239,000 miles (385,000 km).
Stephen Hawking believes that one of the major factors in the possible scarcity of intelligent life in our galaxy is the high probability of an asteroid or comet colliding with inhabited planets.
We have observed, Hawking points out in Life in the Universe, the collision of a comet, Schumacher-Levi, with Jupiter, which produced a series of enormous fireballs, plumes many thousands of kilometers high, hot "bubbles" of gas in the atmosphere, and large dark "scars" on the atmosphere which had lifetimes on the order of weeks.
It is thought the collision of a rather smaller body with the Earth, about 70 million years ago, was responsible for the extinction of the dinosaurs. A few small early mammals survived, but anything as large as a human, would have almost certainly been wiped out.
Through Earth's history such collisions occur, on the average every one million year. If this figure is correct, it would mean that intelligent life on Earth has developed only because of the lucky chance that there have been no major collisions in the last 70 million years. Other planets in the galaxy, Hawking believes, on which life has developed, may not have had a long enough collision free period to evolve intelligent beings.
Comment: By all means read what NASA has to say about it. Then consider this...
NASA warns solar flares from 'huge space storm' will cause devastation ...and what McCanney wrote in Planet X, Comets and Earth Changes: ...before getting the real lowdown on Comet Elenin from these:
Comet Elenin is Coming!
Pole Shift in March? Not Likely!
Comet Elenin: Harbinger of What?
Comet Elenin Update!