This is reminiscent of a game I played online vs players, called Intergalatic, back when I was little. Unfortunately doesn't exist anymore.
Really fun. The controls to this can be a little finicky when selecting the planet to attack, camera control also might need tweaking (maybe an acceleration? why is A zooming out? I tried WASD before arrows, but not really an issue once you figure things out)
Love the gravity/moving planets business though. Adds a new level of strategy.