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Venus, Mars Share Rare Molecule
cndwrld
post Oct 11 2007, 07:33 AM
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Planetary scientists have detected a rare molecule in the atmospheres of both Mars and Venus. The molecule, an exotic form of carbon dioxide, could affect the way the greenhouse mechanism works on Venus.

More information is available at the ESA Venus Express web site at:

http://www.esa.int/SPECIALS/Venus_Express/SEMF8BV7D7F_0.html


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ngunn
post Oct 11 2007, 03:46 PM
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Thanks for posting that. The word 'isotopologue' is new to me, as is the fact that molecular mass asymmetry not only displaces normal spectral features slightly but creates completely new absorption bands. IIRC normal CO2 is not an effective greenhouse gas on Venus because Venus is hotter than Earth and emits mainly shorter IR wavelengths. (I believe it's water vapour that works on Venus as normal CO2 does here.) So this lopsided CO2 and its special effects are a really exciting discovery.
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stevesliva
post Oct 11 2007, 03:56 PM
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Sounds a lot like the discovery of Helium.
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ngunn
post Oct 11 2007, 04:08 PM
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QUOTE (stevesliva @ Oct 11 2007, 04:56 PM) *
Sounds a lot like the discovery of Helium.


Sort of, except that the lopsided CO2 with masses 16-12-18 was already known on Earth, but (I'm guessing because I've only read the press release posted here) the isotopologue absorption at 0.3 microns specifically caused by its asymmetry hadn't been observed in Earth's atmosphere because of its very low abundance.
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nprev
post Oct 11 2007, 04:49 PM
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Hmm. According to this site, O-18 only makes up 0.2% of the total amount of oxygen on Earth (I assume that's the reference area, anyhow). What could have enriched it on Venus & Mars to the point that 16-12-18 was a more abundant molecule on those worlds than on our own?

Only thing I can think of is that their lower gravities may make escape easier for lower-mass isotopes. If true, then we should expect enrichment of heavier gaseous isotopes across the board.


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dvandorn
post Oct 11 2007, 05:09 PM
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Unfortunately, Nick, Venus' mass is very nearly exactly that of Earth -- close enough that I wouldn't expect to see any statistical differences in atmospheric gasses related to escape velocity.

When I look at Venus, Mars and the Earth, and ask myself what atmospheric condition is shared by the former two and not by the latter, the only thing that comes to mind is direct interaction between the atmosphere and the solar wind. Earth's magnetic field wards off the direct solar wind, but Venus and Mars both endure direct impact of the solar wind into their upper atmospheres.

This continual "spalling" of the atmosphere is what has supposedly accounted for the reduction in Mars' atmosphere to such a pitiful remnant at this point in geological time. If Venus has been sans magnetic field for most of its history, you'd have to think it's regenerating its air a lot more robustly than Mars ever could.

But, in any event -- could this unusual concentration of rare isotopes be the result of high-energy interactions between the solar wind and the upper atmosphere? The only other thing I can imagine that would account for it would be differentiation in the solar nebula -- but for that to be the case, you'd have to have a relative abundance of certain isotopes and a "desert" of such isotopes in the band of the nebula from which Earth accreted. Occam's Razor would suggest we're looking at a post-accretion effect and not a question of solar nebula composition.

-the other Doug


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nprev
post Oct 11 2007, 06:22 PM
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I was thinking of accretional effects too, Doug, but couldn't think of a plausible sorting mechanism that would put Earth in an O-18 depletion region. Perhaps we're seeing an artifact of LHB here? Objects that originally accreted in different regions of the solar nebula got swept up, and random (well, assymetrically distributed) isotropic enhancements occurred on the final products...?

Actually, though, I like your thought that the discriminating mechanism might be Earth's magnetic field. That's the only erosion barrier that seems to exist on any of the terrestrial planets with atmospheres, and a paucity of O-16 seems more reasonable then an enrichment of O-18.


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ngunn
post Oct 11 2007, 08:01 PM
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QUOTE (nprev @ Oct 11 2007, 05:49 PM) *
Hmm. According to this site, O-18 only makes up 0.2% of the total amount of oxygen on Earth (I assume that's the reference area, anyhow). What could have enriched it on Venus & Mars to the point that 16-12-18 was a more abundant molecule on those worlds than on our own?


I think this is a misunderstanding. The [i]relative[/u] abundance would be similar everywhere but the absolute abundance would be very low on Earth because here CO2 is only a trace gas to start with, as opposed to making up most of the atmosphere as on Mars and Venus. So you're talking 1 percent of a small quantity giving an undetectable spectral signature while 1 percent of a heck of a lot becomes detectable. I should have specified absolute abundance in my post.
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nprev
post Oct 11 2007, 09:12 PM
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Okay, I'm with you now...funny how assumptions can mess you up! rolleyes.gif So this finding is perhaps not so surprising after all.


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ngunn
post Oct 11 2007, 09:22 PM
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QUOTE (nprev @ Oct 11 2007, 10:12 PM) *
So this finding is perhaps not so surprising after all.


Indeed, it's in the category of could-have-been-foreseen-but wasn't. I like those ones!
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tuvas
post Oct 12 2007, 01:42 PM
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QUOTE (ngunn @ Oct 11 2007, 08:46 AM) *
Thanks for posting that. The word 'isotopologue' is new to me, as is the fact that molecular mass asymmetry not only displaces normal spectral features slightly but creates completely new absorption bands. IIRC normal CO2 is not an effective greenhouse gas on Venus because Venus is hotter than Earth and emits mainly shorter IR wavelengths. (I believe it's water vapour that works on Venus as normal CO2 does here.) So this lopsided CO2 and its special effects are a really exciting discovery.


Water vapor is actually the primary greenhouse gas on Earth, to such an extend that it's maxed out. CO2 isn't maxed out, and that's why global warming scientists believe that it is such a problem, but that's a topic for another thread. Still, the massive amounts of CO2 on Venus, while they might not be in the primary spectrum regions, would still act as quite an efficient greenhouse gas, although water vapor might be more effective there as it is here.
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ngunn
post Oct 12 2007, 02:10 PM
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Nice clarification, thanks tuvas.
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