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Re: bolide physics
>>Thomas R. Holtz, Jr. writes:
>> An additional thought - consider the scale of some of the Jupiter strikes.
>> Many of them were vastly more powerful than anything which struck during
>> the Phanerozoic (540 Mya to the present). If just one of the larger of
>> them had struck the Earth, it would have produced a crater which extends
>> from Washington, D.C. to New York City, and probably have boiled the oceans
>> to a vapor in the process. So much for multicellular life...
>Also, the Chicxulub crater is 180 km or so in diameter. The bolide
>that made it is estimated to have been as large as 10 km in diameter.
>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.
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 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.