Astronomy | Tracking smaller asteroids is no easy assignment On
Feb. 15, a meteor entered Earth’s atmosphere just above
Chelyabinsk, Russia and exploded. It was the largest meteor
since the one that exploded over Tunguska, Russia in 1908. Last
month’s meteor coincided with the flyby of another, larger
asteroid, which came closer to Earth than many communications
satellites. (To be clear: Asteroids orbit in space; meteors are
asteroids that enter Earth’s atmosphere, and meteorites are
meteors that hit the ground.) The big explosion over Chelyabinsk
occurred because the meteor heated up as it passed through the
atmosphere at 40,000 mph. The meteor exploded because of the
difference in heat and pressure at its front and back ends. Last
month’s explosion over Russia is the first recorded since a
meteor blew up over Madrid in 1896, also shattering windows. In
contrast, the Tunguska meteor exploded over Siberia in 1908 with
much more force. It flattened hundreds of square miles of
forest, but there were no witnesse