Introduction
The second planet from the Sun, Venus has no moon,
but is very
similar to Earth in mass and overall density, and is
thought to
have a very similar chemical composition. In many
ways however
the two planets could not be more different. Venus
has an
atmosphere about 90 times thicker than the Earth's,
no appreciable
amount of water, either in liquid form or vapor, and
a surface
temperature high enough to melt lead. Its surface is
completely
hidden from our view because of a thick layer of
clouds made of
sulfuric acid.
These surprising facts came from the exploration
of Venus by the Russian Venera probes, the American
Mariner 10, and
the Pioneer
Venus Orbiters, which explored the planet in the
1970s. In 1975,
the Venera 9 probe was actually able to land on Venus
and snapped
a few photos, just before the planet's harsh
environment destroyed it.
Figure U.1: Venus' surface, photographed by Venera 9
The physical conditions these probes encountered on
the surface of Venus
dashed any of the previous hopes of finding Venus
hospitable to life,
hopes that were based on its size and the fact that
its orbit is not too
much closer to the Sun than Earth's.
More recent data and a deeper understanding of the
geology of
Venus came with the American probe Magellan, which
operated for
about five years in the early 1990s. The Magellan
probe remained
within Venus' orbit, mapping it by
radar with a
detail 10 times
better than the Venera orbital missions of the '70s.
