[chris (OP)]

We know the internal anatomy of the Earth reasonably well thanks for over a century of geological studies, including the details revealed by the propagation of seismic waves; this was the one of the groundbreaking (literally!) discoveries of Croatian polymath Andrija Mohorovičić; I've been privileged to have seen in Zagreb his original notebooks with his calculations to about 5 decimal places in which he traced the latencies and propagation times for Earthquakes; this showed him that the Earth is a bit like an onion inside with different layers at different depths.

But today someone called our Ask! the Naked Scientists radio show and enquired whether other planets have a similar interior, and what we do and do not know.

I was able to point out that we know that Mars, for instance, is volcanic (or at least was); we also know that Venus is probably resurfacing itself regularly.

But presumably we know much less about the internal structure of the other bodies in the solar system, save for what we can infer from similarities or differences with the Earth, magnetic measurements and gravity measurements...?

Can anyone else comment?

[RD]

Mars has been mapped with sufficient accuracy to detect it has a solar-tide ...
http://science.sciencemag.org/content/300/5617/299 *
So it's not solid.

[ * The author of that NASA paper is called Yoder. Sick of the Star-Wars jokes he is  ] 

[evan_au]

The Apollo astronauts left a few seismometers on the Moon, which are triggered by space rock impacts.
This has given some limited idea of the Moon interior.

See: https://en.wikipedia.org/wiki/Lunar_seismology