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Meteorites from Mercury?
machi
post Mar 24 2010, 12:16 PM
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Extinction on Permian/Triassic boundary is probably caused by massive volcanic eruptions (but maybe combined with some impact event).
But Terran meteorites older than 3.5 mld. years can answer the question about beginning of life.


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Rob Pinnegar
post Mar 24 2010, 02:37 PM
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QUOTE (pjam @ Mar 22 2010, 11:15 AM) *
It's true that we can never say `never' for the possibility of meteorites from Mercury, Venus or the Earth. But it's really, really unlikely:


Hi, Phil! Nice to see you here.

I guess there is one other thing for us to consider here besides the initial escape velocity of the material, and that is that any material getting knocked off Mercury would inevitably remain in a Mercury-crossing orbit. Things like the advance of perihelion could keep it away from Mercury for a while, but sooner or later, it would have to encounter Mercury again. If it did so in the "right way", presumably this could give it a bit of an energy boost.

Getting it straight from an initial Mercury-crossing orbit to an orbit that intersects Earth's may be too much to ask for. Alternatively, it could land in a Venus-crossing orbit, giving it the chance to get kicked even further out. But now we're getting into some serious hypotheticals... the odds of any given particle encountering Mercury in a way that just happens to get it back to Mercury, then just happens to get it to Venus, then just happens to get it to Earth? I can picture this happening from time to time -- surely many of the meteorites we pick up here on Earth have experienced multiple planetary encounters -- but it makes things more difficult.
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tty
post Mar 24 2010, 07:08 PM
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The largest (known) young meteor craters are

Kara-Kul, 52 km, c. 5 million years
El'gygytgyn, 18 km, 3-4 milllion years
Zhamanshin, 14 km, 1 million years
Lake Bosumtwi, 10 km, 1 million year

It seems that at least Kara-Kul might be large enough for ejecta to reach escape velocity, particularly as it is at 3900 meters altitude, that means a lot less atmospheric drag (though I guess it was probably rather lower back then). Interestingly it is situated inside the Tien-Shan, so any ejected rocks would be fairly young sedimentary stuff (though I suppose the impact would turn them into instant metamorphics).

As for really old terran meteorites, I've pointed out before that the best (only?) chance to find out anything about what happened on Earth during the first 500 million years or so is probably to look for terran meteorites on the Moon. It seems that the Late Heavy Bombardment wiped out almost every trace of what happened before c. 3800 million years ago.
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pjam
post Mar 30 2010, 04:46 AM
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Hey, that's a good point about Kara-Kul being youngish and fairly large. It's worth a good study, to see if a crater that size and at that elevation could produce ejecta that would escape the Earth. To assess the possibility of Kara-Kul as a possible source for terran meteorites, we need a better understanding of its age and crater diameter, though. It might not be as young or as large as advertised! Unfortunately, it is difficult to do geological fieldwork in Tajikistan these days...

The ejected blocks from Kara-Kul would not be metamorphosed in the normal geological sense by the shock event, they would just be variably shocked pieces of the target rock. A big issue here would be that only the most competent rocks would survive ejection -at least, this is the current argument for why we have only igneous rocks as martian meteorites. The sedimentary rocks on Mars' surface more likely get destroyed during ejection. ...but for Kara-Kul as the terrestrial analogue, maybe limestones are competent enough to act like a basalt and survive ejection during the impact event.

-pjam
Phil McCausland


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"We absolutely must leave room for doubt or there is no progress and there is no learning." -Richard P. Feynman
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stevesliva
post Apr 12 2013, 05:35 PM
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News from the Mercury meteorite front:

Could be:
http://www.planetary.org/blogs/emily-lakda...-meteorite.html

But maybe not:
http://www.npr.org/2013/04/11/176714430/or...e-to-scientists
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TheAnt
post Apr 13 2013, 02:21 PM
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QUOTE (stevesliva @ Apr 12 2013, 07:35 PM) *
News from the Mercury meteorite front:

But maybe not:


Indeed the age is from the very formation of the solar system, which make it quite unlikely that the rock come from Mercury.
The lack of sulphur is another.

As already have been pointed out, it's unlikely but not impossible for a piece of Mercury to get here, so lets see until another candidate turns up.
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