The Comet Nucleus

This is a drawing of what the surface of a comet might look like. Click on image for full size version (40K GIF) Image courtesy of JPL

Observations of the nuclei of comet Hale-Bopp and Hyakutake have given scientists fresh ideas about comet composition and evolution. But, scientists still don't know whether the nucleus is very hard, like solid ground, or very soft and breakable, like a snowball. The Rosetta mission hopes to land a probe on the surface of a comet to find out just how hard it is!

As a comet approaches the Sun, it begins to evaporate, forming the coma and a spectacular comet tail. This picture shows that evaporation may happen only in specific places on the nucleus. These spots of evaporation are called "jets". Halley's comet had three distinct jets on its surface as it approached the Sun in 1986.