Might have been one of the krakens (note: they aren't actually krakens, but bugs that players have named kraken).
Did you leave it on a time accelerated mode? On time-acceleration, the game takes some shortcuts with the delta_t increments that can cause orbits to change when nothing else is acting on the craft. It could have been an impact with debris as well, but that is incredibly unlikely.
Did you leave it on a time accelerated mode? On time-acceleration, the game takes some shortcuts with the delta_t increments that can cause orbits to change when nothing else is acting on the craft. It could have been an impact with debris as well, but that is incredibly unlikely.