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Re: Venus's atmosphere



Referring to this graph of Venusian pressure vs altitude,
It looks like it extrapolates to about 9000 mb at surface level.
or X9 mean sea level pressure rather than X90

<http://www.ebicom.net/~rsf1/vel/1918vpt.htm>

The temperature difference looks more significant in this case.


Brian Whatcott Altus OK

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?


Brian Whatcott Altus OK Eureka!