[meteorite-list] Mercury Fragments on earth (not)

From: Edwin Thompson <etmeteorites_at_meteoritecentral.com>
Date: Thu, 4 Aug 2011 16:07:15 +0000
Message-ID: <BAY168-W15C82A4A2BD3C71361EA58D13D0_at_phx.gbl>

Hi Doug very good to hear from you,

A very compelling poster was presented at a Met Soc meeting back in the 90's showing a very plausible scenario that might have produced meteorites on Earth having come from the surface of Mercury. A number of conditions were taken into careful consideration to lay out this theory on poster paper and the scientist had the guts to put it out there for peer review in from of a very critical community. I remember that a number of scientists came home asking field people at the time to keep an eye out for very unusual types of meteorites, high in metal and extremely weathered because of how long ago this event would have potentially taken place. I did not see this poster but I remember comments at several different well known institutions regarding how well this poster was put together showing the position of the planets and events that would have caused this to occur. Because I was asked by so many different researchers at that time to keep an eye out for the unusual I have always kept that idea in mind as a 'th
ink outside the box project to remember". In passing conversations around the planet with a number of curators back in 2000 it seemed that virtually everyone saw that poster and they were impressed by the potential it provided. Dear friends John Wasson, Paul Warren and Alan Rubin challenged me years ago in one of these conversations to come up with a piece of Mercury and surmised what it might look like. Ever since that intriguing conversation I have watched for anything weird that fit the bill. That's what I thought we had when we took a piece of NWA 6693 to UCLA as soon as we got it. I admit to confess that I thought we had found the golden goose! Still "Super Green" is a super cool chunk of green space rock! Years ago it was thought that Abee was a likely candidate and that the enstatite chondrites were the most likely to be from Mercury because of there age and high metal content and this was all theory long before the 'poster'.

Rubin, if your on-list during this busy time of the year maybe you can name that scientist who presented the mercury meteorite poster and add more specific information to my rather lame rendition.

Doug, always fun to converse with you.

Cheers, Edwin


> To: Meteorite-list at meteoritecentral.com
> Date: Thu, 4 Aug 2011 03:59:37 -0400
> From: mexicodoug at aim.com
> Subject: [meteorite-list] Mercury Fragments on earth (not)
>
> Dear List,
>
> 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
> swinging by.
>
> 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
> angrite theory.
>
> 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
> epsilon.
>
> 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.
>
> Kindest wishes
> Doug
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Received on Thu 04 Aug 2011 12:07:15 PM PDT