Rogue Asteroids
Last Sunday I had a fabulous lunch at Little Cambridge with a few friends and an interesting conversation. Ron told me that he got up one day at some ungodly hour to watch an asteroid. This surprised me a bit. I asked if it was not a meteorite by any chance? No he said, definitely an asteroid.
There are millions of asteroids, literally. Their size ranges from a grain of dust to the 940km diameter of Ceres, the biggest. The vast majority of them belong to the main asteroid belt which is located somewhere between the orbits of Mars and Jupiter. All this is fairly stable, so a collision with the Earth is impossible right?
Not really. There are quite a few rogue asteroids all over the place. It is believed that Jupiter gravity ripped them out of the main belt. Most of the NEA’s (Near Earth Asteroids) belong to four groups called the Amors, the Apollos, the Atens and the Atiras.
The Apollos group alone comprises some 1600 known objects and their orbit crosses ours. So a close encounter or a collision is entirely possible. Ron was right!
Is all that really dangerous? In short, the bigger, the rarer. It is estimated that while a 1m diameter object hits the Earth every 2 weeks, a really big one (like 1000 m) may hit every 0.5 to 1 million years. I am not losing any sleep over this one.
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