Asteroids 

Planetary positions had long been "known" to follow Bode's Law (1772), where the semi-major axis of the planets are given by

a=(4+0)/10
a=(4+3)/10
a=(4+6)/10
a=(4+12)/10
a=(4+24)/10
etc...


 
Mercury
Venus
Earth
Mars
???
Jupiter
Saturn
Uranus
Neptune
Pluto
Predicted
0.4
0.7
1.0
1.6
2.8
5.2
10.0
19.6
 --
38.8
Actual
0.4
0.7
1.0
1.5
???
5.2
9.5
19.2
30.0
39.4

 
 

Size distribution follows a power-law:  Early theory: exploded planet? Won't work: Better idea: Leftovers from early solar system, unable to coalesce into a planet because of Jupiter's gravity.



Orbit classification:

Surface Features

For a long time we had very little idea what the surface of asteroids looked like -- too small, too far away.

On the way to Jupiter, the Galileo probe photographed the surface of a two asteroids - Gaspra and Ida:
 

Gaspra
Ida

 

Ida has a moon! (called Dactyl) (Ida: 58x23 km, Dactyl: 1.6x1.2 km)

Other asteroids do, too. 10-30% of asteroids may have sizable moons (even bigger than Dactyl).

Signs of impacts abound: