There are no other planets. They are entirely alone in their universe, and will simply fly out to eternity in a futile search for other life.

I've heard tales of a giant PacMan who lives in the sky, eating the Icarus gliders who fly too high.

There's one glider that comes back: https://youtu.be/IK7nBOLYzdE?t=112

Those didn’t come back from deep space they simply made a U-turn in low orbit and returned to the surface.

In theory two gliders taking off at the same time at the right distance on a long enough axis could collide in deep space and create something new, which would then return to the planet surface like some kind of invasion, but I doubt it.

I think it must have been made by a glider colliding with something created out there by the collision of two other gliders earlier.