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Re: Greenland Meteorite
Michael Blood wrote:
>
> Mike,
> Ya gotta remember, meteor showers are, essentially, commet trails with
> material no bigger than a grain of rice. The bolide over Greenland was
> emense in comparison - so, comparing their relative speed is not
> aplicable. I believe it is calculated that speads faster than 17 mi. pr.
> sec. will carry a body beyond the solar systems gravitational pull &
> 17mps and slower will result in soloar system incorporation.
> I have not doubt whatever that many on the list know more about this
> than I. Whadda ya say, guys?
> Best wishes, Michael
Howdy Michael,
We can calculate or look-up the escape velocity from the sun but I don't
need to bother- looking at a planetary data table, Mercury's orbital
speed is about 48 km/s, which is well in excess of 17 miles per second.
Escape velocity of course depends on where you are in the solar system
and what velocity you're doing at the moment. Very near the sun it is
whopping large--hundreds of km/s--but an orbiting body further out needs
little boost; e.g., [{square root two minus one} time circular orbital
speed] is a delta-V that can go from circular orbit to escape, applied
correctly. Let's talk elliptical orbits another day.
The mass of the escaping body is not the key. Equate potential energy
and kinetic energy and the mass of the little body is eliminated. Only
the mass of the big old sun is holding the meteoroids back from flying
free to join would-be galactic buddies (I'm neglecting a relatively big
local mass; i.e., the Greenland meoteorite and sun are a two-body
problem til it falls into Earth's "well"). It does not matter that the
Greenland ghost is many orders of magnitude more massive than the tiny
meteor dust referred to in an earlier post, the trajectories are not
(self) mass dependent.
Incidentally, the above considerations greatly relax the requirements on
lifting an object from one of the moons of Jupiter, a past discussion
topic on the list. Remember, even if Jupiter's gravity well exceeds 50
km/s it is unnecessary to fight that since the orbital speed of the moon
gives a goodly boost to begin with. Even with an escape velocity of 2.5
km/s or whatever from the moon in question, numbers under about 10 km/s
can suffice (huge in and of itself, but not an order of magnitude
greater than Mars'). Comets have fallen into Jup faster so could be a
good impact drive to a Jovian moon meteorite. The key is whether
something can be gently propelled from the edge of the shock to escape?
Some armchair physics about not getting Mars escape gently enough for a
meteorite was evidently wrong.
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