A petaton is a unit of mass that is equal to 1,000 teratons. It can also used as a unit of energy equivalent to 1×1015 (one million billion) tons of TNT. This latter use is usually restricted to astronomical events such as meteor impacts or large science fiction weapons.
The energy released by the explosion of one petaton of TNT, 4.18×1024 joules, is equivalent to the energy of an earthquake of magnitude 12 on the Richter Scale, or to the energy of a 60 km rocky meteorite impacting the earth at 25 km/s.