Event Horizon is the long awaited expansion set for the science fiction card game Super Nova.
The supplement features 60 all new cards, including two new alien races, plus new ships, planets, and specials. There's also an all new type of card, the Event card. Event cards are played during the Event phase (a new phase tha occurs right after the Draw phase) and include things like Mass Insanity, Floater Migration, Temporal Storm, and Emperor's Birthday.
Note, however, that this is not a stand-alone expansion. You need a copy of Super Nova.