> Some would think it is luck, like
> falling between Venus and Mars, but I know these things are not by
> chance over many transactions and many changes. There is a law of
> large numbers to consider, plus the fact that Venus somehow has
> avoided its atmosphere getting whisked away like what has occurrd on
You raise a very interesting point. If Venus does have a magnetic
field, it is a very weak one that has so far escaped detection. It
does have what is known as an induced magnetosphere, which is caused
by direct interaction of the solar wind with Venus' ionosphere. That
doesn't happen here on Earth, because out magnetic field protects us.
No seismic data is available for Venus, so we really don't know what
Venus' core is like, although density data for Venus derived from
spacecraft observations suggest that Venus' core is probably similar
in size to Earth's. However, it must be different in some way,
because there is no magnetic field being generated. Perhaps Venus'
core has become completely solid, or maybe completely liquid. Earth,
of course, has a liquid outer and solid inner core.
Even though Venus doesn't have an Earth-like plate tectonic system, it
does have numerous volcanoes, which replenish Venus' atmosphere fast
enough to compensate for the erosive effects of the solar wind. By
some estimates, Venus maye have over 100,000 active volcanoes. That's
the big difference between Venus and Mars. Venus has active volcanoes
to replenish the atmosphere. Mars doesn't.
With all of the active volcanoes blowing out gas, Venus' astmosphere
became denser. Life might have been able to process out some of the
CO2 out of Venus' atmosphere, but life on Venus probably didn't get a
chance to start before it was too late and too hot.