🚀 go-pugleaf

In article MGr@news.cso.uiuc.edu, jbh55289@uxa.cso.uiuc.edu (Josh 'K' Hopkins) writes:
 [ consequences of impact deleted ]
>estimates, but it's important to remeber that as a comet, S/T has a much lower
>mass and is much more fragile than a similarly sized asteroid.  As such, it's
>much less dangerous than an asteroid of the same size.
According to Shoemaker & Shoemaker in ``The New Solar System'', Chap 21
  ``Earth-crossing asteroids are rarely more than 3 km across, [so] most craters
    larger than 60 km [on Earth] probably result from cometary impact.''
But, this is obviously in disagreement with the K/T iridium detection, which implies
an asteroidal origin if extraterrestrial.  The Yucatan impact structure is estimated
to be ~160 km across I recall. They also state that
   ``we suspect that the largest craters on Venus have been produced by comet hits.''
so the atmosphere doesn't appear to help much.  Finally, S/T comes in at a much
higher velocity -- 50 km/s vs 17.5 for an Earth-crossing asteroid (this from
Shoemaker & Shoemaker).  Well actually the vector sum, but still more energetic.
Crater size still estimated at ~20x the diameter of the impacting fragment.   
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Gerald Cecil cecil@wrath.physics.unc.edu  919-962-7169 
Physics & Astronomy, U of North Carolina, Chapel Hill, NC 27599-3255 USA