Comets' Composition

Comets are made of several distinct parts: first of all, there is a solid snowball, called nucleus, made of dust and ice. When the comet comes near the Sun, the nucleus heats up and becomes active, causing volatile gas to sublime. The released gas and dust form a cloud, or coma, and the dust element of the tail.
Let's see in detail the different parts of a comet (click on each term to know more):


  • The nucleus is the relatively solid and stable centrally located part, mostly formed of ice and gas with a small amount of dust and other solids like hydrocarbons. An interesting characteristic of the nucleus surface is the presence of dust ;
  • The coma is a dense atmosphere surrounding the nucleus, made of a cloud of water, carbon dioxide and other neutral gases as well as dust grains. It is formed when the nucleus is heated by the sun, making the gases sublimate, and is later swept into the elongated tails and a huge but very sparse hydrogen cloud (that can measure up to millions of km in diameter)
  • The dust tail is the most prominent part of a comet: it can be up to 10 million km long, composed of smoke-sized dust particles driven off the nucleus by escaping gases;
  • the ion tail is composed of plasma and laced with rays and streamers caused by interactions with the solar wind, which can be as much as several hundred million km long.