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I've watched documentaries about the solar system, where it is suggested that Venus once had oceans of liquid water similar to those that cover most of Earth today. Venus is now in a period of run-away green house effect and has lost its oceans.

I've always wondered whether the apparent over abundance of water on Earth could be partially explained by our planet sweeping up the water, pushed into Earth's path by the solar wind, after it had been liberated from Venus. I know the consensus on where our water came from is a bombardment of comets - but I've always wondered whether some could also have arrived after Venus heated up.

How stupid is this as an idea?

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2 Answers 2

First, one should observe that water is very abundant in the Solar system and most of it comes from before the planetary formation stage. Even Mercury has got its deal of water, albeit a small one.

I think, it will be safer to assume that earth had had it water from the very beginning of its formation.

Additional thing to consider are the temperatures, routinely reachable on various planetary bodies. Mars and everything beyond are way too cool for liquid water to exist, but solid water is present there in considerable quantities. Similarly, Venus and Mercury ended up with temperatures above point of water vaporization or even chemical breakdown in the presence of other compounds. Only the Earth happens to occupy a nice orbital zone where water can exist in all 3 phases (solid, liquid and vapor). But it's not something Venus has any effect on.

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No idea is stupid per se. But in order to place an answer to your question, please consider Venus as a comet. It once had, in that image, a coma (a tail) pointing outwards from the sun, made of evaporated water pushed away by solar wind. How frequently is the Earth exactly inside that coma?

As a comparison, when the Earth strikes a real comet coma we see meteor showers that last no more than one day. So if we consider that Earth may go through Venus imaginary coma once a year, we have an upper limit of 1/365 of Venus' water captured by Earth. This, without taking into effect that Venus had not have a real coma, that evaporation and expelletion of water from Venus was not a so directional process, and surely other factors I can not think about just now.

Besides, do not consider comets the main source of water on Earth. You need to count also with the water vapour generated on volcanoes and that generated on acid-base reactions among Earth's rocks.

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Not sure why you think passing through the coma of every comet occurs in 24 hours or less. A cursory examination of the active periods of the major meteorite showers associated with comets produces active periods of several days to (much less often) several weeks. Venus is considerably larger than any comet I've heard of - so I would predict a large coma. Venus always orbits inside Earth's orbit, in the same plane and direction as Earth - so wouldn't Earth line up in the ideal position for extended periods? –  dav1dsm1th Dec 2 '13 at 22:34
    
I was just stressing the point that water on Earth does not come in its entirety from Venus by presenting a set of very simplified considerations. It is true that Earth lines up with Venus from more than one day, but it is also true that it does not do that once a year but once each 584 days. –  Envite Dec 3 '13 at 6:06
    
I appreciate that, and you taking the time to answer. –  dav1dsm1th Dec 3 '13 at 10:19

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