This mod by iSandor imagines what it would be like if humans managed to colonize Mars.
It adds in a collection of awesome sci-fi bubble houses, all connected by air-tight corridors and walkways. There's a super green communal space, so that your Sims can reminisce about earth, and four houses to live in. One of the coolest thing you can do in Sims 4, and something that everyone always ends up doing anyway, is having babies.
The whole thing is kinda unceremonious in the base game, with kids basically just showing up after a while. The Ultrasound mod by LittleMsSam adds in a nice little touch of realism to proceedings, by adding framed ultrasound pictures that you can put up in your Sim’s home.