If thats true, then why don't we see any effect on Venus? In fact, the uncompressed density of a terrestrial planet (the density it would have if it were not compressed by its own gravity) has a linear dependence of the mass - the compressed density of the Earth is higher than Venus' (by the same amount it is more massive than Venus), higher than Mars (again, linear relationship). The moon is slightly different, but given that it formed out of the Earth's mantle, there's no problem with that. The only planet that does not fit into this scheme is Mercury.

So there is on one hand a dependence of mass, but no dependence of distance. If this is true, the logical conclusion would be that Mercury lost a great part of its mantle.

(If you can read german, look at the following picture I did for another forum: http://www.planeten.ch/images/massedichte.gif, if you can't, here's a short explanation: Masse = mass, Dichte = density, Beziehung = relationship, Unkomprimierte Dichte = uncompressed density, Erde = Earth, Merkur = Mercury, Mond = Moon The dot that is extremely of the line formed by Mars, Earth and Venus, is Mercury, the dot nearer to the line is the Moon)