A Miss is as good as a Mile?

Between the paths around the sun (orbits) of Mars and Jupiter lies the asteroid belt, a swarm of debris left over from the formation of the inner planets- Mercury, Venus, Earth and Mars- some 4.6 billion years ago. Occasionally the planet Jupiter’s gravity nudges some of this debris toward Earth.

Asteroids nudged so that they pass within 121 million miles of the sun are called Near Earth Asteroids(NEA). The ones that get our attention are those that cross the path of the Earth.

In 1908 a NEA about 300 feet across exploded over Siberia leveling over 500,000 acres of forest. About 65 million years before that a really big one, maybe over six miles across, hit near the current location of the Yucatan peninsula of Mexico and is implicated in the extinction of the dinosaurs. So, these NEA’s not only cross Earth’s orbit around the sun, but sometimes get there at the same time we do.

The nearest most recent approaches of NEA’s was in 1998 when one about 1500 feet across came within 64,000 miles of Earth, and in 2002 when another came within 74,000 miles. The Moon is about 240,000 miles from us, so they passed relatively close. Luckily close only counts with horseshoes and hand grenades, but the fact remains, these things do hit us.

In order to detect NEA’s that may be of significant danger, the U.S. Air Force, NASA and others are running surveys to detect and plot the orbits of NEA’s. So far a few thousand have been surveyed; luckily none of these is given much of a chance to hit us. But, as in most things, it is not what you know, but what you don’t know that can get you. A few thousand have been found, but we haven’t found all of them.

In addition to detecting possible impact NEA’s, scientists are researching ways to intercept and destroy or change the course of an asteroid that is heading for a rendezvous with Earth. Several robot spacecraft have been sent to determine just what these things are made of, such as the NEAR Shoemaker mission. The spacecraft flew by and photographed the NEA Eros in 1998 (see image) and landed a probe on its surface in 2001.

Should we worry about getting clobbered by a NEA? I don’t think so, but just to be safe I think it would be a good idea for Earth to keep looking over her shoulder.