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Re: bolide physics



>Dick (sorry, the email address attribution got deleted) wrote: 
>>For reasons having to do with orbital mechanics, any intrasystem bolide
>>is going to be moving at about the same speed as the ones that struck
>>Jupiter. It is likely that a 10-km bolide would release at least the
>>energy of the largest Jupiter strikes, if not possibly more.

then Scott Horton <HORTON@BCRSSU.AGR.CA> wrote:
> Not true. The MINIMUM speed that a bolide will strike a planet is the escape
>velocity of that planet, because it gets accelerated in the planet's gravi-
>tational "well". If I remember correctly, the escape velocity of Jupiter is
>something like 60 km/s. The escape velocity of the Earth is 11 km/s. Yes,
>orbital dynamics may increase a bolide velocity SLIGHTLY in the case of the
>Earth, and VERY SLIGHTLY in the case of Jupiter. Since kinetic energy varies
>as the square of the velocity, a bolide will produce something like 30 times
>as much impact energy on Jupiter as on the Earth.

The worst scenario is that the comet is perturbed from the (still hypo-
thetical) Oort cloud, diving down to a perihelion between earth and sun,
and in a retrograde orientation (counter to earth's motion around the sun).
In this case the relative velocity at impact could be the SUM of:
<escape velocity w.r.t. the sun> and <escape velocity w.r.t. the earth>.

Wouldn't the energy of impact with the earth be GREATER than if the same
bolide hit an outer planet, since solar escape velocity is less out there.
Are you saying solar escape velocity is only a minor component?  Or that
Jupiter is so much bigger it dwarfs the solar component?

Mike Bonham        bonham@jade.ab.ca      Jade Simulations International