I wonder what aliens call earth? Assuming they have visited us in the past, and observed the destructiveness of the human race, perhaps they might have codenamed us: TBD (to be destroyed), or SFE (Scheduled for Extinction)?
Moon is too generic to be just Terra's moon (what about Jupiter's moons), and Earth is equally generic, meaning soil or land, among other things.
http://www.etymonline.com/index.php?term=earth