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Re: bolide physics

> 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 comet fragments that
>struck Jupiter are estimated (from their apparent brightness in a telescope)
>to be a few km in diameter. Thus, yes, the complete comet may have been some-
>thing like 10 km in diameter.
>Scott Horton
>Geophysicist/Computer Programmer

This is only true in a 2-body system.  In multibodied systems, it is possible,
though unlikely, that an impact can occur at lower velocities.  In Jupiter's
case, its moons are relatively small so their affects will be small as well.  
In the Earth's case, our moon is larger relative to the size of the planet, so
is more likely to reduce impact speeds.  

Of course, the opposite is also possible.  I have not worked these types of
equations in many years, so will not try to estimate the scale of the possible
affects from third bodies.  

-Randy King