🚀 go-pugleaf

In article <968@decwrl.UUCP>, liss@gramps.DEC (Frederick R. Liss DTN 237-3649) writes:
>         ....asteroid, by the name of Hermes, almost collided with the 
>         Earth. It only missed us by 500,000 miles, which in 
>         astronomical terms is fairly small. The asteroid was large 
>         enough to do considerable damage to the Earth. Can anyone 
>         supply more information?
Actually, close approaches of this kind, while not terribly common, are
not very unusual, either.  Comet Lexell in the 1700's approached within
0.03 a.u. of the earth, and comets IRAS-Araki-Alcock and Sugano-Saigusa-Fujikawa
in 1983 approached at 0.033 and 0.06 a.u. respectively.  Comet Biela in the
1800's, and Tempel-Tuttle, have approached within 2 million miles in the past,
as has Halley's comet several times in the past 2 millenia.  Consider it this
way, however, and it doesn't seem so peculiar - define an cross section for
collision as the square area subtended by the earth to an oncoming projectile.
If you consider the cross section of a 500,000 mile disk, you'll find that
of random objects moving through this disk, only about one in 15,000 will
hit the earth.  So 500,000 is a very comfortable distance.  It can be
naively argued that the earth's gravitational attraction makes the chances of
collision much greater, but conservation of angular momentum offsets the 
"vacuum cleaner" effect, and causes only a slightly modification to the 
envelope figure of probabilities.

-- 

Don Barry (Chemistry Dept)          CSnet: cmpbsdb%gitpyr.GTNET@gatech.CSNET
Georgia Institute of Technology    BITNET: CMPBSDB @ GITVM1
Atlanta, GA 30332      ARPA: cmpbsdb%gitpyr.GTNET%gatech.CSNET@csnet-relay.ARPA 
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