The planet Venus passed behind the Sun a few days ago, moving from morning sky to evening sky. It's still too close to the Sun to see, though. In fact, we won't get a good look at it until around Halloween.
In a way, Venus is always hidden, because its atmosphere is completely veiled by clouds. Orbiting spacecraft have used radar to peer through the veil, and a few Soviet landers gave us brief glimpses of the surface.
None of those missions has told us a lot about its interior, though. Venus is a little smaller than Earth, but about the same density. That suggests that its interior is similar to Earth's.
We do know that Venus produces no magnetic field. Earth and other planets generate magnetic fields because different layers rotate at slightly different speeds, creating a dynamo effect. But Venus takes eight months to turn on its axis. At such a slow speed, all the layers rotate at the same rate.
We also know that Venus is covered by volcanoes, some of which may still be active. But there's no pattern to them, and there are no geological fault lines, indicating that Venus's crust is a single sheet instead of the overlapping plates that make up Earth's crust.
So the evidence suggests that Venus has a large metallic core, a surrounding mantle of partially molten rock, and a thin crust. But we won't get a good view until we set up instruments on the surface to probe what's happening underground -- something that won't happen for a long time.
Script by Damond Benningfield, Copyright 2011