To answer your question without giving away any story spoilers: You probably noticed by now that as the ash planet loses sand, a group of buildings connected by a bridge slowly appears. Each of those buildings have a teleportation stand that allows you to teleport to a different location. The mechanics of teleportation in the game involve standing on the special teleportation flooring tiles and then looking up. When the planet you are supposed to teleport to intersects with the crosshairs, then you teleport to that location.
Slightly more detailed spoilers on how to get to center of ash twin if you need the help: For ash twin, this is a little difficult because you don't want to get sucked up by the sandstorm, but that's exactly when the planet crosses the teleportation point. You'll want to find some nearby cover and time your jump on the teleportation platform at just the right moment. Dont forget to look up.