| It is indeed likely that a substantial amount of gas from the initial nebulae was still present as planetesimal accretion started. |
| After all, planetesimal sized portions of the Solar System cannot be considered to be orbiting the Earth, except in the obvious case of the Moon. |
| His greatest contribution, however, was his planetesimal hypothesis of the origin of the planets. |
| Models of planetesimal disks suggest that low relative velocities between the bodies produce accretion rather than fragmentation. |
| Fortunately, the worst of the radiation is blocked by a dense planetesimal debris field, but there is still significant ultraviolet backscatter. |
| Should this gas be dense enough, then it would tend to align planetesimal orbits, hence lowering their impact velocities. |
