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Meteorite from Mercury?
texchanchan writes "The BBC reports that a chunk of rock, clearly from space, might have originated on Mercury. Analysis of its chemical makeup leads to this tentative conclusion. Specifically, it seems to have originated on something with 'a core of molten iron [and] an outer covering of silicon and aluminium that formed a basaltic crust.' This meteorite classification site sticks to the earlier theory that NWA 011 is from a Vesta-like source."
just to get it out of my system completly.
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Mercury has a fairly large iron core and a very thin layer of crust. The spectroscopy matches Mercury but I'd do more testing(especially ones looking for cosmic rays) before I count out a wayward asteroid.
The BBC article has very few details, so I tried to track down more information on it. I found a recent paper in Science which appears to be about this meteorite (Yamaguchi et al, Science 2002, vol. 296).
However, in the article there is no claim to it coming from Mercury (rather it is a new type of basalt). Am I missing somebody else's intrepetation of the data, or is this media spin?
Warning: Some ideologies on the Net are smaller than they appear.
The abstract of the article in Science doesn't mention Mercury either. (Nosy free registration required.) I don't know where the BBC got the idea. It would be cool (hot) if it was true, but don't know who originated it. Another note about the meteorite, referring to "another Vesta," but not Mercury.
OK, when the "Mars meteorite" was announces a few years ago I could possible see how they could claim to know that it originated from the 4th planet. We've send a few space probes to Mars and have been able to study (at least remotely) the make-up of certain regions on that planet. But to say that this chunk of rock is from Mercury is a bit of a streatch, IMHO. Those minerals are also abundant in asteroids. It's times like these that showcase how boundless our ignorance of our own solar system truly is.
The impression I got from the BBC article was that the meteorite came from a body considerably larger than Vesta. I'm not sure how that oxygen-isotope thingy they're talking about works, but if it's deficient in the chunkier elements, that would imply - to my mind - that it came from a big-assed body. If that's the case - and we can assume it's not from the moon or Mars - then it must've come from a really big asteroid, or from Mercury.
So people're inferring that it's from Mercury through a process of elimination. Seems reasonable to me.
Why emilinate a larger asteroid? The asteroid belt constantly has collisions and destruction of the objects. It's actually easy to imagine that there were once much larger asteroids in the belt, and they have since been shattered.
I find it easier to believe than to believe that a rock was blasted off of Mercury and then somehow made it to Earth's orbit.
If you really want to know where it came from, we'll need a close look at Mercury. Last I heard, the European Space Agency's Mercury mission included a lander, so we might be in luck.
Oooh, this chunk of rock came from Mars! This one's from Mercury! Hey, this one's from the planet KRYPTON! (is it green or red I wonder?)
/. wouldn't take the huge bn.com link.
All this stuff seems to be based on what Frazer called "the magical laws of similarity and contagion" rather than real science. I tried to link Frazer's magnum opus The Golden Bough here but
It's a logical fallacy to assume that object A was once a part of object B simply because they share the same composition; in fact it's a bad idea to blindly assume object A came from B even if A is identical to an object you know came from object B!
Pseudo-scientific psychobabble by fuzzy thinkers in search of grant money? Or just bad reporting?
Why emilinate a larger asteroid?
The very nature of the asteroid belt is such that huge asteroids are unlikely (note: IANAA). Jupiter's gravitational influence would stop bodies of sufficient size from forming; loose agglomerations are possible - even likely - but these wouldn't, TTBOMK, be sufficiently packed for their own gravity to allow the iron to sink into the centre.
Sorry, but nope. Several asteroids where are now in the belt are massive enough to be spherical (that's a self-gravity effect) and be differentiated, Ceres and Vesta amoung them. Since we get metallic and stony meteorites on Earth, we know that some large asteroids which were differentiated must have existed only to be blown appart in a large collisions. Since we know that this erosion has been happening, there is no real reason to assume that the current asteroids are the largest that have ever existed. In fact, I can see a case that it is unlikely that Ceres is the largest asteroid to ever inhabit the asteroid belt. (Without knowing how much destruction has happened, I couldn't say off-hand.)
:-)
Note: I am an astronomer
Funny... I always thought Ceres was much smaller than that. And if one can be that big now, I can't in all honesty argue that there weren't bigger ones in the past. Bugger.
/. readers know I'm an idiot. Hooray!
Now all I need to do is try to be happy that I've been corrected rather than disgruntled at having my spurious pontification shown to be in error in front of millions of erudite personages.
No, wait... only
I just want to live up to your so-elegantly stated expectations... your mastery of the language is impressive!