Re: Venus's atmosphere

[Gary Karshner <gkarshner@STMARYTX.EDU>]

Frank,
        The atmospheres of the terrestrial  planets are thought to be
secondary in the sense that  the gasses that make them up are from volcanic
out gassing. Both Mars and Venus have high carbon dioxide abundances
because of it higher molecular weight 44 verse 28 and 32 for nitrogen and
oxygen. The interesting question is what happened to the Earth's carbon
dioxide. Of course some of it recently became oxygen, but the bulk of the
Earth's carbon dioxide reacted with our large abundance of water to become
limestone, marble, etc. It the Earth's over supply of liquid water that did
the chemistry to remove it. Water on Venus would be gaseous and not
dissolve the calcium so it could react with the dissolved carbon dioxide.
        Liquid water on Earth shaped is planet in many ways. I would say
we are lucky it's here except we wouldn't be if it wasn't!
        A question I have wondered about is what happened to the water
vapor on Venus?
Hope this helps.
        Gary

At 11:07 AM 7/23/2003 -0400, you wrote:
> Why is it that Venus has been able to retain an atmosphere that exerts a
> pressure about 90x that of the atmosphere on Earth?  The mass of Venus is less
> than that of Earth, so its gravitational acceleration is only 8.9 m/s2.  Its
> atmosphere is hotter (about 737K vs. 288K).  Even though its atmosphere is
> mostly
> CO2, with a molar mass of 44 compared to an average of about 29 for Earth's
> atmosphere, it seems counterintuitive that it could retain such a dense
> atmosphere compared to Earth.  Even when you factor in that at higher
> temperatures
> gases exert greater pressure with less molecules/volume, this is only a
> factor of
> about 2.5.
>
> I cannot find any explanation of this, although I imagine there are many
> available--just can't find them.  Many Websites even discuss the factors that
> allow a planet to retain an atmosphere and then give many
> examples--Mercury, the
> moon, Mars, etc. that go along with the smaller mass, less gravity, less
> atmosphere argument and "higher temperature-less atmosphere" argument, but
> then they
> never explain Venus.
>
> Anyone have a reasonable simple explanation?