Comets & Cometary Activity: Advanced Connections

An inactive comet consists mainly of a solid nucleus containing ice, dust, and refractory material. Near the Sun it develops a coma, a curved dust tail, and an ion tail that points more directly away from the Sun under the influence of the solar wind and magnetic field.

As the nucleus warms, volatile molecules sublimate and drag dust from the surface. Radiation pressure pushes dust away gradually, while ionized gas couples to the solar wind and is carried anti-sunward. Repeated perihelion passages erode and alter the nucleus.

Misconception: A comet's tail always trails behind it in the direction opposite its motion.

Correction: Comet tails are controlled mainly by sunlight and the solar wind, so they point broadly away from the Sun and can appear ahead of the comet after perihelion.

Comets preserve primitive material from cold outer regions of the early Solar System and connect the Kuiper belt and Oort cloud to the inner Solar System. Their compositions help constrain the delivery of volatiles and organic molecules to young planets.