I am, so far, unless I skipped a response, seeing people talk about Earth's reaction.
Titan was fully self-sufficient until they had an accident at their research base, which destroyed a third of the habitats and wiped out the tillable soil. They had no long-range communications, so they send a ship which promptly says hello to a torpedo or a phaser from an Earth ship. They then go on a rampage, wearing outfits which make them look alien, terrorizing Earth.
In all that time of coming up with an answer to their crisis, did they not consider contacting other settled places, that we know of and those we don't know about? It did feel like the writers forgot that humans had colonized more than Titan.
Known places:
Venus - undergoing terraforming in the 2370s, probably a colony soon after
Moon - colonies
Mars - Hundreds of years later, atmospheric fires could have stopped, rebuilt takes place afterwards
Jupiter - a giant station in the 24th century and outposts and a colony on Ganymede ("By Any Other Name")
Looking at a list from Wikipedia on where humans could colonize, there are options at Neptune (moons), at Uranus (moons), and, adding a personal favorite here, Pluto.