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Posted by robert casey on December 3, 2007, 4:48 pm
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From Sky and Telescope web site
http://www.skyandtelescope.com/news/home/12082586.html
"The other result to report is that hydrogen and oxygen are readily
escaping from the planet, likely stripped away by the solar wind as it
races by. Now, Venus hasn't had any water to speak of for billions of
years. It probably boiled away when the planet's runaway greenhouse took
hold early in its history. That catastrophic loss left the remaining
airmass enriched in a heavier-than-normal isotope of hydrogen called
deuterium. An atom of hydrogen can escape to space more easily than one
of deuterium, and scientists realized in 1978 that the ratio of
deuterium to hydrogen in Venus's atmosphere is 150 times greater than it
is in terrestrial seawater.
But what's fascinating is that the D:H ratio is even higher (2½ greater)
in the planet's upper atmosphere, 50 to 60 miles up. Why so? One
possibility is that Venus is sweeping up water from passing (and
colliding) comets, and cometary water has a huge excess of deuterium.
The problem is that the atmosphere has far less water vapor on top than
it does lower down — a puzzling result for which investigator Jean-Loup
Bertaux and his experiment team have no explanation."
Maybe I'm missing something, but isn't the upper atmosphere the place
where the planet loses the water/hydrogen and oxygen? And wouldn't the
heavy hydrogen (deuterium) have a better chance of staying around then
the light (regular) hydrogen)? So the D:H ratio would be higher in the
upper atmosphere. As it is, both hydrogen and deuterium are escaping,
but the regular hydrogen escapes faster. SO that would be why water
vapor is scarce up there. Yes?
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