This is an essay written some years ago by the late Tom Van Flandern which was included in his book ‘Dark Matter, Missing Planets & New Comets’. Tom, who worked for many years at the U.S. Naval Observatory, was an out of the box thinker who covered a wide range of astronomical topics, many of them well outside the mainstream. His methodology was a bit similar to my old dad’s approach to cryptic crosswords. “The clue doesn’t give you the answer, but it helps confirm you got the right answer once you’ve got it”. Leif Svalgaard says he was a crank, which in my view means he’s well worth a read. I think this article, tied in with his other solar system formation concepts, deserves to be republished for the assessment and re-appraisal of the talkshop cognoscenti and the interested visitors here.
Let us examine in detail what the consequences would be of assuming that Mercury originated as a satellite of Venus. If that were so, we might presume that Mercury formed in close orbit about Venus, perhaps by fissiona. But Mercury is four and a half times more massive than the Moon. So the interchange of energy through tidal friction between Venus and Mercury would have been enormous. Mercury’s original spin would have been halted fairly rapidly by Venus, leaving Mercury spinning once per revolution around Venus, always keeping the same face toward Venus, as for our Moon.