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RalofTyr
2008-Feb-12, 08:42 PM
I read somewhere, probably here, that the early sun only shone about 70% of what it does now. My question is, with that in mind, was Venus in the habitiable zone early on with liquid oceans and perhaps, as the sun heated up, the oceans boiled away. When did this occur? Was it early on...or maybe as late as a billion years go?

01101001
2008-Feb-12, 09:15 PM
My question is, with that in mind, was Venus in the habitiable zone early on with liquid oceans and perhaps, as the sun heated up, the oceans boiled away. When did this occur? Was it early on...or maybe as late as a billion years go?

Planetary Society News: Venus Express: Venus Express Pulls Back the Veil from Earth’s Mysterious “Twin” (http://www.planetary.org/news/2007/1130_Venus_Express_Pulls_Back_the_Veil_from.html)


If, as most scientists believe, early Venus, like the early Earth, possessed oceans, the excessive heat would cause more water to evaporate than on Earth, increasing the proportion of water-vapor in the atmosphere. [...] At some point this positive feedback loop will raise surface temperatures above 100 degrees Celsius, and practically boil the oceans away.

I don't find there an actual when. Suspecting something happened, and finding evidence that supports the event, may not necessarily determine, even roughly, when it happened. For instance ABC News in Science: 'Evil twin' Venus astounds astronomers (http://www.abc.net.au/science/articles/2007/11/29/2105074.htm?site=science&topic=latest) only narrows it down to:


Liquid water oceans may have been present on Venus as recently as 1 billion to 3 billion years ago, [Dr Hakan Svedhem, Venus Express team project scientist] says.

But, maybe someone else knows of better estimates.

Noclevername
2008-Feb-13, 12:48 AM
I read somewhere, probably here, that the early sun only shone about 70% of what it does now. My question is, with that in mind, was Venus in the habitiable zone early on with liquid oceans and perhaps, as the sun heated up, the oceans boiled away. When did this occur? Was it early on...or maybe as late as a billion years go?

Since we don't actually know the outer limits of the habitable zone, only that Earth is in it, we can't know if Venus was ever in it. We also have little actual direct evidence that there were oceans on Venus.