From the December 2006 issue

How do spacecraft safely navigate the asteroid belt?

JOHNATHON GREEN, ANCHORAGE, ALASKA
By | Published: December 1, 2006 | Last updated on May 18, 2023
Mathilde
Unlike Hollywood depictions, the asteroid belt, located midway between the orbits of Mars and Jupiter, is mostly empty space.

Imagine the asteroid belt as a disk-shape region with its inner edge at twice Earth’s distance from the Sun (186 million miles). The outer edge reaches to 3 times Earth’s solar distance (279 million miles), and the disk is about 9 million miles thick. The patch of space containing the asteroid belt has a huge volume — 1 trillion trillion cubic miles. That’s a lot of space to fill.

There are hundreds of thousands of main-belt asteroids known, and many more await discovery. If, as some estimates suggest, a million objects lie in the asteroid belt, then the average distance between asteroids is 730,000 miles (1.1 million km).

So, the asteroid belt is hardly a dense debris field. It’s easy for spacecraft to miss asteroids, given such large gaps between them. —Bill Cooke, NASA/Marshall Space Flight Center, Huntsville, Alabama