Asteroid of varying sizes streaks toward Earth every second.
If a bigger stone threatens the planet it will take 800 trillion terajoules — compared with the 418,000 terajoules produced by history's most powerful blast, the Soviet Union's test detonation of the "Big Ivan" hydrogen bomb in 1961 to shatter or redirect it
Most researchers regard a nuclear explosion as an option of last resort, however – something to try if the clock is really running out.
With years or decades of lead time, a so-called "gravity tractor" probe could be launched to rendezvous and fly with the asteroid. Over time, the spacecraft's subtle gravitational tug could pull the space rock into a more benign orbit.
Or a kinetic impactor could be slammed into the asteroid in deep space, knocking it onto a different path. But this might be tough to achieve when it is the 600-mile-wide "Armageddon" asteroid, which is about the same size as the dwarf planet Ceres.
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