February 20, 2013 | 14 When a 17-meter asteroid barreled into
Earth’s atmosphere over central Russia on February 15, releasing
a powerful shock wave that injured more than 1,000 people, many
observers wondered how such a momentous event could arrive
unheralded. The fact is, the object that exploded in a fireball
over Chelyabinsk, releasing hundreds of kilotons of energy, was
small potatoes. There may be millions of comparably sized
objects in the inner solar system, only a small fraction of
which have been discovered. The searches to date have been
focused on tracking much larger dino-killers and other
potentially catastrophic asteroids and comets—those objects
larger than about one kilometer. So the door has been open to
unpleasant but ultimately survivable asteroid surprises. Several
new and forthcoming projects will amass reams of new data about
the near-Earth asteroid (NEA) population, but a comprehensive
catalogue of Chelyabinsk-scale objects remains beyond the
technological horizon. The asteroids are to