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The Mystery of Comet Hyakutake

On April 4 1996, it was announced that a team of U.S. and German scientists had detected strong X-ray emissions from the comet Hyakutake. This is a surprising discovery because such a cold body as a comet was not expected to be a source of intense X-rays. Also surprising is the rapid changes in strength and intensity which seem to coincide with chunks of the comet breaking off as it heads towards the sun.

Photo of the comet taken on March 27.

The physical process producing these X-rays is a mystery. Normally, X-rays can be produced if high-energy electrons are rapidly accelerated or decelerated. The earliest laboratory source of X-rays was a vacuum tube containing a heated tungsten filament as a source of electrons, and a metal target. The electrons emitted from the filament were accelerated across the space by a high electric field until they hit the solid target where they collided with the metal atoms, thus converting some of their kinetic energy into electromagnetic energy (in the form of X-rays), and the rest as heat. But it is thought that the density of electrons and other ions hitting the comet is insufficient to create such intense X-ray emission.

Another theory is that the radiation from the sun is absorbed by the cloud of gaseous water moleculed surrounding the nucleus of the comet, and is then reradiated as X-rays. However, the crescent shape suggests that the sun's radiation is bouncing off the top layer of the comet's cloud almost as if it was a solid surface, instead of a fairly tenuous gas.

"You would expect to see right through to the center. But the X-rays (from the sun) are being stopped, which is very surprising," said NASA astrophysicist Carey M. Lisse.

White crescent-shaped area shows the X-ray glow on the leading edge of the comet

What do you think might be the explanation? Is the X-ray emission entirely due to the solar wind impinging on the comet? Or is there a stranger explanation? Is there something unusual about the comet Hyakutake? Or is it just another dirty snowball?
Send us your theories by e-mail to Computer Futures, Inc.

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