To the production facility, it's probably easier to keep 1 blank in than to remove it from the stack. AFAIR, the total number of cards in the game is an odd number; production is probably simpler if you add that extra card. Or something.
It is just an extra card from the sheet. This happens often with punchboards too. It is not worth tooling a whole new machine for one small difference on one board so they just have the same punch pattern and on the last board it ends up punching a blank space.
Its a divider. With this card the publisher can show the printer where one card deck on the sheet ends and another begins. In this case it helped to divide the card deck from the "Small Asteroid" promo cards on the same sheet.
Blank cards can be used to replace other cards (with the same back) that get marked, or to create your own card ... or to pretend you have the promo card if it has the right back (I don't recall) ... so I appreciate the blank as a backup for the inevitable card that gets wet or stepped on.