 Complete the following phrase:  The Sentry Risk Table estimates that Apophis would impact Earth with kinetic energy equivalent to 1,200 megatons of TNT. The impacts that created Meteor Crater, Arizona about 50,000 years ago and the Tunguska event of 1908 are estimated to be between 310 megatons. The biggest hydrogen bomb ever exploded, the Tsar Bomba, was around 50 megatons, while the 