Recently, I have discovered that a ship/vessel in the orbit of an alien planet will vanish for no apparent reason. Initially, it occurred very infrequently, but it is becoming more prevalent as the game progresses. The first few times it occurred, I searched the star map in vain to find them, but then noticed that race's Military rating decreases each time. Lately, however, an orbiting ship will vanish at a planet that is in view when I click the Turn button but I never see it leave even when my picket ships are in range of the planet. I also checked any of that race's nearby planets to verify that the missing ship didn't just change locations. Does anybody know why orbiting ships disappear? Are they being mothballed/destroyed for cash?