Close Calls

Two asteroids will zip past Earth today, both well inside the orbit of the Moon. Both are small-- only tens of feet across-- which accounts for the fact that they were only discovered recently. Neither poses a threat to Earth.

Still, they are reminders of the threat posed by such roving rocks. Objects the size of these two, if they did hit Earth, could explode in the atmosphere, or, reaching the surface, could do serious local damage. Hitting the ocean, a rock that size could raise a tsunami.

Astronomers say such close calls are fairly common, but two in one day are rare.