Thank you for your replies.
Yes I felt the shaking of the "force" too
.
I am glad that I am not the only one who had this experience, because otherwise I would start to doubt about my mind. I have the savegame before this "event" and repeated the turn and this time the planet did not disappear!!!
It really seems to be random and therefore it is not much use to send it to MM.
However I continued my game in the "mystery" Version without my precious colony.