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The Question
(Submitted July 16, 1997)
I have read the article on the X-ray emissions from comet Hyakutake.
Your hypothesis on the water cloud around the nucleus is interesting but
did you analyze the same activities on comet Hale-Bopp?
If so what are other hypothesis or conclusions?
The Answer
Last May in Baltimore, Maryland, USA we had a meeting of all the
people interested in the cometary X-ray emission problem. the first time
all of us had gotten together since the discovery in 1996. We now have
detections of X-rays from some 8 comets, and all bright, nearby comets
seem to emit X-rays! (Including Hale-Bopp, although it was much fainter than
we expected in the X-ray for such an optically bright and productive
comet. It has been proposed that the extremely large amount of dust
emitted by the comet, as compared to other comets, may be somehow
damping the X-ray emission.)
At the meeting, it became apparent that 3 mechanisms are possible
causes of the emission, in oder of likeliness: charge exchange between
solar wind heavy ions and cometary neutrals, bremsstrahlung emission,
and magnetic field recombination. All of these mechanisms involve interactions
between the solar wind and the comet's extended atmosphere and ionosphere.
It is clear that we need more observations to figure out exactly what
is going on, though! But it does seem that we will be able to use the X-rays
to probe the nature of the solar wind and magnetic field throughout the solar
system.
Hope this helps!
Casey Lisse
for Ask a High-Energy Astronomer
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