How do space probes make it past the asteroid belt without crashing into asteroids?
Category: Space Published: January 20, 2013
By: Christopher S. Baird, author of The Top 50 Science Questions with Surprising Answers and Associate Professor of Physics at West Texas A&M University
The asteroid belt between Mars and Jupiter contains millions of asteroids, but a space probe has never had to worry about hitting into one on its way to the outer planets. The reason for this is because space is so big and so empty when it comes to macroscopic objects such as planets and asteroids. Outer space is crammed full with microscopic particles and fields, but when it comes to an object big enough to crash into, they are very rare. Space is so big and so empty of rocks on average that unless a space probe intentionally aims towards an asteroid or a planet, it will miss. This is one fact that Hollywood usually gets wrong in order to increase the drama. When a space ship in a movie finds itself in danger of crashing while trying to navigate through an asteroid field, be aware that you are watching pure fiction. In the Backman Report, NASA estimates the natural collision rate between two asteroids in the asteroid belt to be once every ten million years. Therefore, assuming a space probe moves at speeds comparable to an asteroid and is around the size of an asteroid (both reasonable assumptions), a space probe would not hit an asteroid in the main asteroid belt for ten million years, even if flying around blindly.