1.3 billion tonnes
Sounds like alot, but the moon already weighs 50 billion times that much. I doubt we'd even notice. No one expects real science in typical sci-fi, but this is the kind of detail they could have so easily looked up, like I just did. It shows a total lack of caring.
Another way to put that figure in perspective (of some strange sort) is that Earth itself has lost more mass than that due to escaping hydrogen since dogs were domesticated.