By Ron Miller — Sometimes the line separating "asteroid" from "comet" is a blurry one. For instance, there is the strange asteroid Chiron. Discovered in 1979 by astronomer Charles T. Kowal, it was cataloged as asteroid number 2060. But almost immediately, it was recognized as being a little weird.

First, because its orbit turned out to lie between Uranus and Saturn...much further from the sun than any other asteroid. It also had the strange habit of seeming to change its brightness. In 1988, astronomers William Hartmann, Dave Tholen and Dale Cruikshank noticed that Chiron was nearly twice as bright as it was supposed to be. The asteroid continued to brighten, eventually becoming three times brighter than usual. What was going on?


The answer was that Chiron contains a lot of ice and as its orbit carried it closer to the sun, some of this ice turned to gas. A huge cloud of gas and dust was forming around the asteroid. In effect, Chiron had turned into a comet.

Then, astronomers observed an event recently that was similar but even more spectacular...

It was discovered by the Lincoln Near Earth Asteroid Research (LINEAR). This is an MIT project jointly funded by the United States Air Force and NASA. One of its goals is to detect and catalog near-earth asteroids that might potentially threaten the Earth.


On January 6 it found an object that was cataloged as P/2010 A2. This turned out to be something so unusual that last week the Hubble Space Telescope was focused on it. What Hubble revealed is an object that is almost completely unique. At first glance, it seemed to be comet. But the 460-foot nucleus was offset from the tail, which had a very unusual structure near the nucleus. And there was no discernable gas in the tail. Since P/2010 A was located in the asteroid belt, scientists are speculating that it may be the result of a collision between two asteroids. Such a collision would have occurred at over 900 miles per hour—-five times the speed of a rifle bullet. This would have released energy equivalent to an atomic bomb, creating a cloud of dust and debris. This cloud was then blown by the pressure of sunlight into a long, trailing comet-like tail

P/2010 A gives scientists a glimpse into the early history of our solar system, when similar collisions between planetesimals eventually created the planets we know today—-including our own earth.


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