And more importantly, once they had boldly gone where no one lese had gone before, what happened to all those uninhabited planets, Class M and otherwise, after they left?
The next wave of human development would occur, just as it had in earlier eras on Earth - settlers and others would follow, looking to stake a claim.
Some would be mined, like that planetoid in the episode "Devil In The Dark". Others would be exploited for other natural resources.
And some would be transformed into getaway resorts!
In the 'Doctor Who' episode "Midnight", the Doctor and Donna traveled to the planet Midnight (ironically named because it is always bathed in extreme deadly sunlight. Even though exposure to the surface could kill you, still somebody saw fit to build a resort there. (Probably for the tourist attraction of the sapphire waterfalls.....)
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Molto bene!
Because the Leisure Palace appears to have been built and then lowered onto the planet's surface in the first rush after discovery, I'm thinking the lack of proper investigation into the planet's properties (which would have discovered the alien presence) means that this episode occurred early in Man's piglrimage to the final frontier. And this resort would fit perfectly with the main reason Mankind pushed outwards to the stars -
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So I'm thinking that on the Toobworld timeline, "Midnight" should be placed somewhere between 'Star Trek' and its sequel eighty some-odd years down the road, 'Star Trek: The Next Generation'. And it was at a time when 21st Century fashions were back in vogue, judging by how everyone was dressed among the passengers. (Behind the scenes, it was a good way to keep down the budget on such a "bottle show".)
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Toby OB