MadSci Network: Astronomy

Re: At what temperature would water boil on Venus?

Date: Mon Mar 26 10:46:18 2001
Posted By: Erika Gibb, Grad student, Physics & Astronomy/Origins of Life, RPI
Area of science: Astronomy
ID: 985279413.As


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!


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