On Thu, 2010-01-07 at 13:48 -0800, Alastair wrote:
> In general, any existing asteroid with and Earth-crossing orbit is not
> going to hit the earth now, since it has been missing us for 4.600
> billion years! In other words, Earth crossing asteroids are the the
> exceptions that prove the rule.
Ever been to Meteor (Barringer) Crater, in Arizona USA? It is an
impressive sight. Or hear anything about the strange geology under the
Yucatan? Or under Chesapeake Bay? There are more than 150 identified
craters on the Earth's surface, and most of them are less than a billion
years old. So why didn't these hit the Earth during the previous 3.600+
billion years? In the case of the Chesapeake crater, how did it miss for
4.565 billion years?
Orbits change. Asteroid orbits can change slowly, by perturbation and
more subtle processes, and rapidly with a near passage to a planet, or
even near passage to one of the more massive asteroids (Ceres, Pallas,
Vesta, and a dozen others). Planet orbits change as well.
> I've run http://www.orbitsimulator.com/ (Thanks Phil :-) with one
> asteroid that had an orbit greater than any at present but less than
> that of Jupiter. Its orbits slowly filled the space between Mars and
> Jupiter, and probably would have continued to fill the space as far as
> Earth. Left longer yet it could have reached Venus, but if it had
> already collided with Mars or Earth that would not happen.
Glad you like it. Running one orbit is interesting, but if you would
like to get a better understanding, try some close passages, both of
Jupiter and other planets. These might be even more interesting. Don't
use just one asteroid, run 10 or more with very slightly different
starting parameters. If they stay clumped, try again, getting closer to
the planet, or perhaps just simulate for more time.
--
Phil Hays <[email protected]>
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