Asteroid Belt Facts
1) Position in the Solar System: 5th planetary orbital position
2) Minimum distance to Earth: Approximately one AU
3) Orbital inclination to ecliptic: Main belt--<4 degrees
4) Orbital eccentricity: Main belt—0.33
5) Diameter: Main belt—Approximately 3 AU
6) Mass: Main belt—est. 22X106kg, 10x106lbs
7) Largest object in main belt: asteroid Ceres—974 km, 604.2 miles, in diameter (recently reclassified as a minor planet)
8) Number of known objects in main belt: 100,000; most are pebble size—16 have diameters of at least 240 km, 150 miles.
91) Types of asteroids: 3—
- Carbonaceous or C-type (make up 75% of asteroids—very dark);
- Silicaceous or S-type (appx. 17% of known asteroids—fairly bright composed of rocky material)
- Metallic or M-type(fairly bright, composed of iron)
Recent probes by spacecraft seem to indicate that many asteroids are mostly ice, similar to comets.