FLW: Dirty Snowball

This model was first proposed by Fred L. Whipple in 1950.

 

It is based on the assumption that everything in the solar system is stratified, with rocky materials nearer the Sun, and lighter gases further away. Since comets exist in the region thought to be comprised mainly of gases, comets should be made of ices (water, carbon monoxide, carbon dioxide, etc.) with spinklings of the dust from which the solar system originally condensed.

 

The cometary tails are then erosion from the surface, due to friction with the solar wind.