|MadSci Network: Astronomy|
Adam, As you state, the temperature at which a substance boils depends on the pressure exerted on it. In general, increasing the pressure increases the boiling point. Earth has an atmospheric pressure of about 1 bar on the surface (where a unit of pressure is the force pushing down per unit area - 14.7 pounds per square inch on Earth). Venus, on the other hand has a 90 bar atmosphere which corresponds to >1300 pounds per square inch. This raises the boiling temperature of water significantly. On Venus, water would boil at ~375 F. The surface temperature on Venus is about 900 F, well above the boiling point even for its high atmospheric pressure. There cannot be any liquid water on Venus. While early in its history, Venus may have had as much water as Earth, most of it was lost. Over time, the Sun's UV rays would have broken water vapor in the atmosphere apart into hydrogen and oxygen. Venus is not massive enough to retain the hydrogen and it would have escaped. Currently only about 1 in every 30,000 molecules in Venus's atmosphere is water. Venus is a very dry planet indeed! Erika To learn more about the solar system, check out http://kids.msfc.nasa.gov/SolarSystem/ and http://pds.jpl.nasa.gov/planets/
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