Voxels can't move. The engine doesn't like it very much if you try. So instead, the real planets are spawned many hundreds of thousands of km from the center and fake proxy planets will move around in their stead. When you approach one of the proxies, you will teleport "seamlessly" to the real planet and can land on it from there.

The velocity of entities will be changed to match the coordinate system of the new zone. For instance, if you are standing still in space and a planet orbits into you, you will suddenly be travelling towards it at the same speed it was orbiting. This can be dangerous if you aren't careful!

There is also a distinction between the "ORBIT" and "SURFACE" zones for planets. In the ORBIT zone, you will follow the planet along its orbit while the planet spins beneath you. In the SURFACE zone, you will follow the planet's surface while the sky and stars spin around you. When you are not near enough to any planet to be within its zone, you will be in the PROXY zone, which is the default zone that doesn't move.

When entities transition between zones, all entities nearby will transition with them. In theory everything is offset the exact same amount during the teleport, but in practice it isn't always perfectly clean (especially in MP). This can be potentially hazardous if you are walking around inside of your ship or are dampened to it. For safety, you may want all players to remain seated when transitioning between zones.

In addition to the orbit and day cycle customization, you can also set the Proxy Scale of a planet. This will make the planet larger or smaller in proxy space without changing the size of the actual voxel planet. This can allow for life-size planets in proxy space without breaking the engine with an oversized voxel planet. You could also make the planets much smaller and closer together in proxy space to make interplanetary travel much easier if you prefer (all distances between planets in proxy space will be smaller).

The SE engine has a tendency to break down in various ways when travelling at uncapped speeds, but there are ways to avoid the worst of them, so here are a couple pointers:

1. (speed > 1000 m/s) Moving around as a player inside a ship at these speeds is very difficult and may see you clip outside the ship or get splattered.
2. (speed > 10,000 m/s) Ships with subgrids may generate collisions between their subgrids that take a very long time for the engine to process. The game may freeze for several minutes if this happens, so avoid using any subgrids (or keep them locked so that they don't move around) if you want to go any faster than this.
3. (speed > 150,000 m/s) Any grids that travel faster than this may have their velocity glitch out and get stuck moving at 800,000 -1,000,000 m/s. This can be fixed by finding the grid in the entity list and Stopping the grid several times.

So in summary, if you want to explore the solar system at extreme speeds: stay in a cockpit at all times, avoid using any subgrids, and set the global speed limit < 150,000 m/s. Enjoy!