Your only hope of survival is to find a way of hopping from one celestial body to another staying one step ahead of Planet X.
Inspired by a short story by Italo Calvino, “The Distance of the Moon” http://www.aleastory.co.uk/The-Distance-of-the-Moon.pdf
“This is how we did the job: in the boat we had a ladder: one of us held it, another climbed to the top, and a third, at the oars, rowed until we were right under the Moon; that’s why there had to be so many of us… from the top of the ladder, standing erect on the last rung, you could just touch the Moon if you held your arms up…. I would cling first with one hand, then with both, and immediately I would feel ladder and boat drifting away from below me, and the motion of the Moon would tear me from the Earth’s attraction. Yes, the Moon was so strong that she pulled you up; you realized this the moment you passed from one to the other: you had to swing up abruptly, with a kind of somersault, grabbing the scales, throwing your legs over your head, until your feet were on the Moon’s surface.”
The solar system that you are in is very compressed and and each planet has multiple moons with wildly elliptical orbits, which at times take them so close to their planets and each other that they are almost touching.
So the game play is to build structures to be able to transfer from one body to another when they cross each other’s path. Each Planet/Moon being a level with it own unique problems (i.e. different gravity, raw materials, distances to transverse, lack of oxygen, etc.)