Rule 717.6 · Attraction Cards
If a card with an Astrotorium card back would be put into a zone other than the battlefield, exile, or the command zone from anywhere, instead its owner puts it into the command zone. This replacement effect may apply more than once to the same event. This is an exception to rule 614.5.
Subrules
Each card owned by the same player that has been put in the command zone this way is kept in a single face-up pile separate from any player’s Attraction deck. This pile is informally referred to as that player’s “junkyard.” The pile is not its own zone.