Comet Facts

Scientists call comets “dirty snowballs,” because they are mainly made up of frozen methane, ammonia, and water.

Comets are smaller celestial objects that orbit the Sun with orbits that are very elliptical, often bringing them close to the Sun.

The key characteristic of a comet is that when it does get closer to the Sun, the ice inside begins to melt causing bright features, including the well-known comet “tail.”

Each time a comet becomes warm enough, it “sheds” part of its contents, giving scientists the theory that comets have a limited lifespan.

How many comets are there

The scientific community calculates that there are around 3,000 comets, with one occurrence visible from Earth every ten years.

Humans have been viewing comets for thousands of years and, since comets may eventually shed all of its contents, scientists believe that they would have ended their existence a long time ago.

Therefore, there must be a location in the Solar System that is producing comets. Since the outer Solar System is the only place that hasn’t been deeply researched, it’s assumed that this is very likely the birthplace of comets.

Scientists have been studying the orbits of comets and there is evidence that there may possibly be two places in the outer Solar System that are producing comets.

The closer area is the Kuiper Belt, which has already been found to contain a band of comets that share similar shorter orbital traits to those seen in the Asteroid belt.

Further out is a spherical shell called the Oort Cloud and those comets that originate in this area seem to have a longer orbital pattern.

Theories on exactly how comets begin in any of these areas include the idea that they exist as objects and due to collisions with other comets may be knocked into new orbital patterns that are due to the gravity pull of passing interstellar objects, including planets.

What happens when a comet come close to the Sun

When a comet comes close to the Sun and their internal ices begin to melt, they have bright features that show. There are 4 parts to these comets: the nucleus, coma, dust tail, and ion tail.

  • The nucleus is the center most part of a comet that is made up of rocky materials and ice. A majority of the comets have a diameter of between 10-100 km, although some have reached 100 km in diameter.
  • The coma is the gases that surround the nucleus. These are clouds of mixtures of ammonia, water vapor, and carbon dioxide.
  • The dust tail is made up of tiny dust particles and gases that are blown away from the nucleus when it becomes heated. When we see a comet in the night sky, the most notable part of the comet is the bright wisp of the dust tail.
  • The ion tail results from contact with the solar wind and is ionized gases that are streaming and blown away from the Sun.

Famous Comets

Over thousands of years astronomers have made note of some of the comets that reappear after durations of time. Some of the most famous include:

  • Halley’s Comet: Visible every 75-76 years, it was discovered in 1705 by Edmond Halley when he was studying other comet orbits. This comet was originally observed and reported in 1531, 1607, and 1682. Halley came to the conclusion that this was the same comet repeating its orbit. The comet was then named after Halley.
  • Comet Shoemaker-Levy 9: Another name for this comet is SL 9, and was actually a string of comets that were discovered in 1994 by Gene Shoemaker, Carolyn Shoemaker, and David Levy. Most well-known for being captured by Jupiter’s orbit, the string of comets crashed into Jupiter leaving a brilliant display for study by scientists.
  • Comet Hale-Bopp has an orbit of 2,300 years and was named for the two people that discovered it: Alan Hale and Thomas Bopp. While it is known in the scientific community, it became renowned for the California cult that thought the comet was a spacecraft.


  • What are the two locations that scientists believe are the birth place of comets?
    Kuiper Belt and Oort Cloud
  • What are the 4 parts of a comet whose orbit nears the Sun?
    the nucleus, coma, dust tail, and ion tail
  • Name one of the most famous comets.
    Halley’s Comet, Comet Hale-Bopp, or Comet Shoemaker-Levy 9
  • What planet did a string of comets crash into that was visible from Earth?
  • What nickname are comets sometimes called?
    dirty snowball
  • How many comets do scientist think exist?
    around 3,000