Ask A Scientist© Astronomy Archive

Question:  What is the composition of Venus? I can't find it anywhere.
Kjones

Answer:  I've looked through several astronomy texts, and there are some guesses 
about the internal composition of Venus. We'll have to wait for a lander
mission (almost certain to be unmanned, given the hostile Venusian en-
vironment) designed to probe the interior before we know for sure.
  First, the overall density is 5.24 grams per cubic centimeter, compared
with Earth's 5.52 grams per cubic centimeter. (We can measure the physical
dimensions of the planet, and by noting its gravitational influence on
an orbiting satellite like the Pioneer Venus Orbiter, we can calculate
Venus' mass. Then Density=Mass/Volume.) This tells us that the internal
composition and structure of the two planets may well be similar, and
current theories of planet formation would support this.
  Venus has almost no magnetic field, which suggests that it may not have
a liquid iron core, as the Earth does (although this may also be simply
because Venus rotates so much more slowly than the Earth).
  The USSR landed several probes on the surface since the 1970's which
measured (among other things) rock and soil composition. These probes
found granite-like materials and basaltic rock. The latter is almost
certainly due to lava flows (which may still be going on).
  In sum, current best guess is that the composition of Venus is similar
to that of Earth, though probably not identical to it.
  I got the above info from: "Exploration of the Universe" by Abell,
Morrison, and Wolff; "The Solar System" by Encrenaz and Bibring; and
"The Solar System" by B.W. Jones (you may need to go to a university
library to find books like these).
Rcwinther