MadSci Network: Astronomy
Query:

Re: Are there liquids on Venus? II.

Date: Wed May 18 22:44:39 2005
Posted By: John W. Weiss, Grad Student in Planetary Science
Area of science: Astronomy
ID: 1115405220.As
Message:

Actually, at Venus's temperatures, liquid water is not possible regardless of pressure. Increasing pressure definitely increasing boiling point, but there's a limit to that. Above around 600 Kelvins (or about 900 degrees Celsius), the liquid and vapor phases become merged and water only exists as a kind of gas. You can see this on a phase diagram of water if it shows enough of the temperature and pressure range.

What about other liquids? I have been unable to find any references which suggest liquids on the surface of Venus. And based on spacecraft data, there aren't any large-scale liquid features at present. (Also, the landers didn't see anything. But the landers didn't have a very wide view, either.) Which isn't to say that there could never be any. I'm sure if we looked for a while we can find a substance which is liquid under those conditions. But it isn't enough to simply be able to find a compound that can do something: it has to exist in appreciable quantities on Venus, too. And there isn't that much there: carbon dioxide, sufluric acid clouds (the H2SO4 only exists above a certain altitude; below that, near the surface, it's too hot), and basaltic rock pretty much covers most of it.

It is true, mountains would have the best chance for most liquids since they're coolers. But "cooler" is a comparative word. The temperature atop the tallest mountains on Venus is only about 100 degrees Celsius below the surface temperature. (The "lapse rate" on Venus is about 10 degrees per kilometer, comparable to what we get on Earth. The tallest mountains are about 10 km high. So the total drop is around 100 degrees Celsius.) That still makes the temperature quite high, above 600 K (330 degrees C), so it's probably too hot still for any substances on Venus to be liquids. On the other hand, the mountains are quite probably covered in a metallic frost, so the temperature difference is at least a little bit important for some things.

If you're looking for a good book on Venus, I recommend David Grinspoon's Venus Revealed. It's a good read and very informative. I hope this answer has been helpful!


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