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Re: Close-Call Asteroid Coming

>Hopefully my 9:10 a.m. posting will help to clarify the potential
>impact scenario for those a little less versed in impact hazard. I may
>not know much (yet) about meteoritics ... but at least I can converse
>on this aspect fairly well.  

Yes, your posting summed it up very well.

>Hopefully after reading up on some of the
>references I gave (a thimblefull of what I've got on it), they'll
>understand the difference between a "city" and a "continent"
>catastrophic event, and give you a bit of breathing room.

The objects we are most concerned about are the Potential Hazardous
Asteroids, or PHAs.  These are objects that are estimated to be 150 meters
in diameter or larger, and whose orbits come within 0.05 AU of the Earth's
orbit.  Smaller objects can still do damage if they impact the Earth, but
the damage is more localized, such as was the case with Tunguska.
The damage of a PHA impact is much more substantial with a much higher
potential for an adverse effect on Earth's entire ecosystem.

>One thing that perhaps you may be able to answer for me, though ... how
>does specific gravity effect impact liklihood? Obviously the ejecta
>would be greater, etc., but ... as an example ... would the moon be
>more or less prone to impact than Earth? 

The Moon is a smaller target, and has a lower gravity well, so is
less prone to be impacted by the larger asteroids/comets.

Ron Baalke

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