The
‘bit of a stretch” comment in the same context as
” just like we have Martian meteorites” is
intentional. The gravitational
forces on the Earth are higher, and there is a dense atmosphere related to
Mars. It takes a much bigger impactor on earth to
eject material at escape velocity than it would on Mars. Therefore, the amount
of available material that could possibly find it’s
way back to Earth would be much less and should be rather rare. Who knows: as rare as a Venusian meteorite? No one has every classified one
but you can bet your helmet that they are here somewhere. We only know that
Mars and Lunar materials are here because we have been to those places and
analyzed the chemical and geological properties of rocks, which were mostly
basalts.
The angle of impact would not be that important with an impactor like Chixilub, Sudbury, Vredfort, Chesapeake and
probably Manicouagan.
The size of these bodies would eject material even on a
zenith trajectory. They would also punch
such a vacuum hole in the atmosphere that it would suck out great quantities of
molten matter that would go into earth orbit and most likely reenter the atmosphere
producing tektites.
The point here is that it does not require an extreme amount
of physics to understand that there are pieces of this entire solar system all
over the place. We just have to look at all of the impact craters that we can
see in our neighborhood to understand that every planet has probably traded
material with every other over the course of the last 4 billion years.
CharlyV
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED]
Sent: Friday, February 13, 2004
11:13 AM
To:
[EMAIL PROTECTED]
Subject: Re: [meteorite-list]
Iranian Fireball Was Of Geophysical Origin
This topic was discussed a few weeks
ago on the list, and it seems pretty convincing that Earth parented meteorites
are elusive for good scientific reasoning - it seems that if conditions to
produce them happened, that the material would be glass or a split planet Earth
(a la did the moon come from Earth question we had recently).
While it may be possible (though statistically highly improbable), it is
important not to say it is "a bit of a stretch", "just like we
have Martian meteorites here".
Those statements taken together are misleading, to say the least.
It is important to recognize that Earth and Mars are so different regarding
atmospheric density (over 100X) / viscosity and to a much lesser degree
gravity, that such an analogy is not based on astronomy and physics, but rather
wishful thinking, with a general ignoring of scientific principles - i.e. a
solution (Earth parented meteorites exist because I can think it and there are
Martian meteorites here) looking for a problem (Why no one has ever confirmed
an Earth parented meteorite).
Extending that logic, I would ask where the Solar parented meteorites are at,
and while we are at it the Jovian parented and Venusian parented
meteorites as well. The conditions on Mars simply do not lend themselves
for comparison to Earth. Venus is a better comparison for Earth.
Perhaps someone could work out the physics to show what sort of impactor on
Earth is capable of causings something besides glass and giving it escape
velocity.
Without doing the physics, it is clear it would have to be a kilometer plus
sized impactor imparting in an instant to a kilometer plus sized Earth rock
escape velocity plus frictional loss velocity, which further does not explode
with that velocity at sea level as it makes its way through the exponientially
most dense part of the atmosphere (i.e. a "reverse meteorite") at a
right or obtuse angle to the impact (which tends to create a velocity vector
landing back on Earth). While this might sound "plausible", for
an impactor to produce a kilometer plus sized rock with such a velocity seems
nearly impossible, knowing the characteristics of Earth surface features.
To actually achieve the above, either ground zero has to become liquid or
plasma eventually producing glasses, for which there is some evidence in
tektites, or Earth must be split like a nut, for which the Moon was presented
as evidence in such a hypothethised impact around 4.5 billion years ago....
So that would leave a scenario of a gigantic impactor hitting near the base of
a Mount Everest made of solid iron or other high tensile type structure,
incoming at a low entry angle, and propelling the peak into outer space.
In the case of Mars objects over 10 meters (but probably in the realm 500 km)
can impact whole much more readily and produce "reverse meteorites"
with the initial velocities potentially conducive to this event which can
escape more readily as gravity (and hence resulting escape velocities) is less
than 40% Earth's. Furthermore Mars is closer to the Asteroid belt and is
expected to have more flux of such potential impacts.
Saludos
Doug Dawn
Mexico
En un mensaje con fecha 02/13/2004 8:21:52 AM Mexico Standard Time,
[EMAIL PROTECTED] escribe:
and bit of a stretch.. but
plausible: Just like we have
Martian meteorites here on earth, so would we not have some of the
ejecta from our terrestrial impacts also in orbit around the Sun
