Asteroids: Where in the Solar System?

There are lots and lots of asteroids: over 150,000 of them have orbits known well enough that they have been given official identification numbers. Here is a top-down view of the inner Solar System showing the location of the planets Mercury through Jupiter, known comets (white symbols), and the locations of all 150,000+ numbered asteroids on April 1, 2007.

The Asteroid Belt, top view

NASA/JPL Image

Here is a side view of the same objects on the same day.

The Asteroid Belt, side view

NASA/JPL Image

Most of the asteroids orbit between Mars and Jupiter. This is the main Asteroid Belt, and it contains nearly all of the asteroids. A few asteroids form clumps in the same orbit as Jupiter, but 60 degrees ahead and behind that giant planet. These are called the Trojan asteroids. Finally, a few asteroids cross the orbits of the inner planets, including the orbit of Earth. Those that come close to Earth are called Near-Earth Objects, and those are the ones we carefully watch. (Don’t be fooled by these images!)

The five planets in the images move in nearly circular orbits that are all in nearly the same plane. Most of the asteroids in the main asteroid belt have circular orbits too, but they can also be found far above or below the plane of the planets. Some asteroids have non-circular orbits. You can see the orbits of individual asteroids by using the Small Body Database Browser at NASA’s Jet Propulsion Laboratory (JPL) web site.

Just type in the name or number of an asteroid like Ceres (which has a nearly circular orbit) or Apollo (which has a non-circular orbit) in the box and hit “Return.” That will take you to a page with lots of information about the asteroid. To see the asteroid’s orbit, and click on “Orbit Diagram.” Using the tools in the window that comes up, you can pan and zoom on the asteroid’s orbit, and make it move forward or backward in time.