Meteorites from Mercury? Options

[Guest_Enceladus75_*]

I see in the current issue of Astronomy magazine (November 2008) that there is a very interesting article about a class of meteorites that are theorised to have possibly originated on Mercury. We now know of meteorites that came from the Moon and Mars, and there might also be some from Venus, but I think that it is fascinating that we may have, right here on Earth, pieces of the innermost planet at hand.

Would it take a sample return mission from Mercury to prove these meteorites came from the planet or could the Messeneger results in the coming years clinch the question?

What do others think?

[nprev]

Wouldn't it be a bit hard to identify a Terran meteorite? There are many processes that can mimic fusion crust (ex: 'desert glazing'), and the isotope ratios would obviously not differ from Terrestrial norms. It'd probably just look like an unremarkable metamorphic rock.

With respect to Mecurian & even Venusian meteorites, one exciting thing to think about is that we KNOW they're here, if quite rare. It's a statistical certainty that N>0 no matter what. For all we know, any of us may have kicked one at some point in our lives. The trick is to identify them chemically, and that really does seem to require ground truth from both bodies.

[pjam]

Wouldn't it be a bit hard to identify a Terran meteorite? There are many processes that can mimic fusion crust (ex: 'desert glazing'), and the isotope ratios would obviously not differ from Terrestrial norms. It'd probably just look like an unremarkable metamorphic rock.

With respect to Mecurian & even Venusian meteorites, one exciting thing to think about is that we KNOW they're here, if quite rare. It's a statistical certainty that N>0 no matter what. For all we know, any of us may have kicked one at some point in our lives. The trick is to identify them chemically, and that really does seem to require ground truth from both bodies.

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:

Mercury: Hard to get out of the sun's gravity well, so meteorites not only need to be ejected from Mercury (relatively easy) but they need to get out to the Earth too. Hey, maybe that Venus flyby would help!

Venus: Big planet and thick atmosphere + interior to Earth.

Earth: Here's the rub -objects liberated from the Earth have a dynamical lifetime of some few millions of years, after that they are nearly all swept up or otherwise removed from orbit. So... for any reasonable possibility of terran meteorites, we would need to have had a large impact capable of liberating meteoroids from the Earth sometime, say, within the last 10 million years. There are no such young, large impacts known.

...but I think there is still an interesting possibility of locating older terran *fossil* meteorites, if one could demonstrate the presence of a fusion crust on a fossil meteorite recovered from rocks that shortly postdate known major impacts. The point is, these meteorites would not be falling anymore now, but they might exist in the sedimentary rock record.

-pjam