Alas, one less mysterious plot device for scifi (see Earth, by David Brinn)

Solving the Biggest Natural Explosion in Modern History – 1908 Tunguska Event – Popular Mechanics: ”

When Comets Attack: Solving the Mystery of the Biggest Natural Explosion in Modern History
On the morning of June 30, 1908, the sky exploded over a remote region of central Siberia. A fireball as powerful as hundreds of Hiroshima atomic blasts scorched through the upper atmosphere, burning nearly 800 square miles of land. Scientists today think a small fragment of a comet or asteroid caused the ‘Tunguska event,’ so named for the Tunguska river nearby. Now, a controversial new scientific study suggests that a chunk of a comet caused the 5-10 megaton fireball, bouncing off the atmosphere and back into orbit around the sun. The scientists have even identified a candidate Tunguska object—now more than 100 million miles away—that will pass close to Earth again “