[meteorite-list] Mercury Fragments on earth (not)
From: MexicoDoug <mexicodoug_at_meteoritecentral.com>
Date: Thu, 04 Aug 2011 03:59:37 -0400
Mercury as a source for meteorites arriving on earth seems like the
most unlikely occurrence. I hope someone can point out where I am
wrong, since it would be wonderful to imagine the possibility that
material from the Swift Planet could every make the upstream trip here.
It is easy to think hey ... we have Lunar and Martian material here,
dream of Vestal material, so why no Mercury, Venus, etc... as if all
were equally possible.
But they are not equally possible. Far, Far, Far from equally
possible. If things were equally possible all you would have to do is
ask two supermodels out on a date, and odds are one would accept,
right? - There are only 2 answers and *if we assume yes/no is a 50/50
proposition...* ? Hmmm ... a most unlikely occurrence.... and for most
not a 50/50 probability. Same goes for this present case.
The Moon is obviously within Earth's gravitational domination, so it is
natural that we would have a high possibility if material falling here
if it can escape the moon (escape velocity: 2.4 km/s), and Earth is the
local drain for the moon.
Mars (escape velocity: 5.0 km/s) is upstream from the Sun to Earth so
it doesn't seem like any surprise that fragments ejected could find
their way to Earth.
So why not a Jupiter meteorite? I don't think that is likely since
Jupiter (escape velocity on 'surface' 59.5 km/s) extremely greedy with
its material, requiring escape at five times faster than on Earth.
But what about Mercury. Mercury's escape velocity is 4.3 km/s. But
it's downstream from Earth and the Sun is a huge gravitational drain
plug that devours material. If you think Earth gets a piece of Mars,
imagine what the Sun gets from Mercury. To escape the Sun ... that is
to go upstream towards Earth, at Mercury, any fragment would have to
battle an escape velocity of 67.7 km/s. That's greater than Jupiter !
You might say ... ok, you don't have to actually escape the Sun, only
make it from Mercury to Earth. Well, at Earth, the escape velocity is
42 km/s from the Sun. That's a loss of 25 km/s ... and don't forget
the extra 4.3 km/s to get away from Mercury as well ...
Their numbers are probably greater than summing them, but let's just do
that so it stays simple call it a minimum of 30 km/s imparted velocity
to tether that fragment of Mercury to Earth. What lucky rock ejected
by chance in the direction of Earth could handle that energy and board
a greyhound (bus) to Earth?
It seems to me about as likely that we'd get a fragment from Jupiter's
surface if indeed there is a surface instead of a thick damping stew.
Once something (plasma?) gets ejected from Jupiter, though it is smooth
sailing to Earth if the direction happens to be right because the Sun
still sucks up anything not in a circular or ellipsoid orbit, like the
big drain hole that got the whole solar system moving to start with.
(Yes, everything orbits the Sun for pretty much the same reason the
water makes circles around the hole in toilet bowl on its way down).
So if by brute force, Mercury is unlikely to be a source of material,
how about by some other celestial mechanism? Something similar to
Jupiter's orbital resonances, perhaps? I don't think that is very
likely. Earth would be the Jupiter by mass, though Venus might be
argued. But Mercury is not the Swift Planet for nothing ... there is
no way orbital resonance could build up with Mercury constantly
It gets rapidly less likely anything else might work ... like, how
about a hand-off from Mercury to Venus then to Earth. The energy is
still huge to get to Venus, but unless JPL tweaks a slingshot out of it
with the assistance of propulsion, I just don't see it happening.
Well, then I would think the argument dropped to a statistical one ...
It would be ... very very unlikely but when 10,000,000,000 pieces are
ejected from Mercury and 0.000001% actually do this *a miracle happens*
and we are left with 100 meteorites that make it to Earth. OK, but by
the same logic then there would be 1,000,000,000 lunar meteorites lying
around. So go find one ... no ... make that go find two - from
Mercury, I mean. Angrites are more than two... Kind of weakens the
The last resort might be to argue a hugely eccentric orbit with a major
axis reaching earth. I don't know about this one, but there is the
detail of Venus clearing its own neighborhood, not to mention Mercury
and Earth runs at a snail?s pace compared to them. There are no
Vulcanoid asteroids and so, so so few Interior earth Asteroids ...
like a dozen? And how eccentric are their orbits ... Maybe some
asteroid scanning guy can speak authoritatively here but I have a
feeling that the answer won?t budge from almost nothing to nothing plus
Anyway, ET's angrite without equal and amazing story of adventure that
goes with it ... got me to thinking about the debate we've heard many
times now and when I look at these numbers, I just can buy it. Is
there some other argument being made that was omitted here ... besides
Mercurians shooting at Earth with scaled up accelerator space guns? I
hope so, but darned if I can think of it! The situation is very
different from Vestoid since there is no supraJupiter undisturbed ...
around with billions of circulating rocks smashing into each other much
further away from the Sun's powerful gravitational grasp.
Received on Thu 04 Aug 2011 03:59:37 AM PDT