# How do probes get through the asteroid belt?

There’s a huge belt of asteroids past the orbit of Mars. How do we manage to get probes past all that floating rubble? Is it dumb luck or do the probes navigate around the asteroids?

Real asteroid belts aren’t like Star Wars. ISTR that if you flew from Mars to Jupiter, the total number of asteroids you could expect to be able to see with the naked eye would be about 1. So it’s not like you have to make a huge effort to avoid them.

Yeah, the volume is so huge and the asteroids are so small that it would be a matter of hitting the lottery to have one plow into a probe.

We also know where all the big asteroids are, so any potential collisions can be eliminated beforehand.

As long as we’re Seeming To Recall, ISTR that the average distance between asteroids is about a million miles.

Yeah, and most people don’t realize it, but it’s easier getting thru the asteroid belt than it is landing on a planet, like… oh… say…

Mars.

–grumble grumble, stupid hamsters–

What everybody else said. The asteroid belt doesn’t look the way it’s typically shown in movies. Sure, there are thousands and thousands of rocks, but they’re spread out over trillions of cubic miles.

Imagine five golf balls distributed over a football field, then extrapolate to several thousand football fields: The actual asteroid field is far less dense even than that. I’d imagine it’s something like an M&M every fifty city blocks, at best.

So, obviously, a probe’s risk of hitting something is quite small indeed. In fact, just the opposite: It takes a lot of specific effort to get the probe to get anywhere near anything of interest.

Well, ISTR reading an illustration of this. It said that if you were standing on a certain asteroid, in the most densely populated section of the asteroid belt, you would be able to see a grand total of three other asteroids with the naked eye. If you were lucky.

One thing to note is that unlike the planets, the asteroids often have large inclinations. The inclination is how much the orbit is tilted with respect to that of Earth. Planets have at most about 2 degrees of inclination[sup]1[/sup], while asteroids are up to about 40 degrees or so. This means that many asteroids are quite a ways above or below the plane of the planetary orbits for most of their orbits.
[sup]1[/sup] Not counting the largest member of the Kuiper Belt as a planet, a common error.

Are you dissin’ my boy Pluto?

And here I was thinking all it took was the right vector and a liberal application of astroglide!