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                    $B9V1i(B Prof. J. M. Greenberg$B!J%i%$%G%sBg3X!K(B

                         $B!X(BMaking a Comet Nucleus$B!Y(B

  Comet nuclei are the most primitive objects in the Solar System. They have
preserved the material out of which the SS was born in a collapsing
interstellar cloud of gas and dust 4.6 billion years ago  The chemical
composition of a comet nucleus is derived from the interstellar dust as it
existed in the protosolar cloud with the constraint that the abundances of
the elements are the same as those in the SS. Although comets are usually
thought to be like dirty snowballs it can be shown that only about 30% by
mass is frozen H2O, the rest being divided approximately equally between:
other frozen volatile molecules, complex organic molecules, and silicates.
This would be better called a frozen mudball than a dirty snowball.

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Room:$BM}3XIt(B3$B9f4[(B307$B9f<<(B
Phone: 011-706-3567 Fax: 011-746-2715
E-mail: keikei@ep.sci.hokudai.ac.jp
URL: http://www.ep.sci.hokudai.ac.jp/~keikei