Anatomy of a Comet
A comet can accurately be described as a “icy dirtball” or “dirty iceball.” As the iceball approached the inner solar system, the increasing warmth of sunlight caused the ices (typically water, carbon dioxide, methane, formaldahyde, etc.) to vaporize. The ices vaporize and are ionized by solar radiation before being swept back by the solar wind to produce the ion, or plasma, tail. As the ices vaporize, they in turn free the trapped dust which produced the dust tail. The plasma (ion) tail always points in the anti-solar direction while the dust tail is swept back along the comet's orbit.
A comet is the only celestial body that by international agreement can bear the name of the discover(s).
The prominent parts of a comet and typical dimensions are given below:
Nucleus: 6 miles
Coma: 600,000 miles
Hydrogen envelope: 6 million miles
Dust tail: 60 million miles
Ion (plasma) tail: 60 million miles
Because the vaporized ice is ionized by the solar wind, the ice particles have an electric charge and interact with the solar wind. Thus, the ion tail is swept back by the solar wind and always points away from the Sun. This means that the ion tail may at times follow the comet—when the comet approaches the Sun—or precede the comet as it moves away from the Sun.
Once liberated by the vaporized ices, the dust reflects sunlight (producing the yellow-white color we see) and spreads along the comet's orbit. As the dust trails the comet and dissipates, the dust could produce a meteor shower if the earth were to cross the comet's orbit.
The various components are labelled in the photograph below:
