^I don't need one. I just need to know the most elementary things about how Mars was perceived at the time. Nobody in 1964, or ever, would've thought that Mars was a better exemplar for an Earthlike planet than Earth was. It's just a non-starter.
Since I never claimed that Mars was "a better exemplar for an Earthlike planet than Earth", that doesn't have any bearing on what I said either.
Somehow you seem to require that the process that led to the selection of the letter must make total scientific sense, even though we both know that much of the point in selecting just a letter in the first place was to avoid committing to anything that might be contradicted by science. As long as the technobabble plays its part convincingly as part of the scenery, what difference does it make whether the babble was devised by the writers in complete adherence to scientific principles? If anything's a non-starter here, it's the argument that only sensible backstories can stand behind what's seen and heard on screen. Star Trek
would never have made it on the air, if that had been the yardstick by which all its backstory was judged. I'm rather surprised that you
need to be reminded of that.
Anyway, "mesoplanet" is as good a retronym as any. I certainly like that better than Minshara,
because "mesoplanet" is at least meaningful. I'm happy to see real science picking up that term; it's good publicity for Star Trek.