A small object made of ice, dust, and rock that has a long orbit

Comets are cosmic snowballs of frozen gases, rock and dust that orbit the Sun. When frozen, they are the size of a small town. When a comet's orbit brings it close to the Sun, it heats up and spews dust and gases into a giant glowing head larger than most planets.Comet nuclei are loose collections of ice, dust and small rocky particles, ranging from a few kilometers to tens of kilometers across. As a comet approaches the inner solar system, solar radiation causes the volatile materials within the comet to vaporize and stream out of the nucleus, carrying dust away with them. The streams of dust and gas form a huge, extremely tenuous atmosphere around the comet called the coma, and the force exerted on the coma by the radiation pressure of the Sun and solar wind cause a tail to form. The tail always points away from the sun.

Explanation:

Each comet consists of the following:

1) Nucleus, consisting of a stable, porous central mass of ice, gas, and dust. Generally, it will be between 1 - 10 km/0.6 – 6 miles in diameter. The ice contains varying amounts of water, carbon dioxide, ammonia, and methane; the dust may contain various mixtures hydrogen, oxygen, carbon, nitrogen, silica, and some metals; and, traces of hydrocarbons may also be in the nucleus.

2) Coma, which is the visible, cloud-like atmosphere;

3) Dust Tail, which consists of a long, streaming-appearing tail of dust particles reflecting sunlight; and,