What Are Comets Made Of? (Composition By Parts)

Comets are made primarily of dry ice, water, ammonia, methane, iron, magnesium, sodium, and silicates. Due to the low temperatures of comets, these substances are frozen.

The Solar System was born as a result of a huge cloud of gas and dust, which collapsed 4.6 billion years ago.

Halley comet

Most of the cloud, flattened into a disk around a young Sun, clumped together to form the planets.

However, some small chunks remained and became chunks of frozen gas and dust, living in the outer region of the Solar System, where it is cold enough to make the frozen ice creams that give comets their tails.

How are comets formed and what are they made of?

Comets originate in the outer solar system and tend to be constantly affected by the approach of the larger planets, causing their orbits to constantly change.

Some are taken to orbits whose trajectory makes them travel very close to the Sun, destroying themselves completely, while others are simply sent forever out of the solar system.

Astronomers maintain that comets are composed of materials from the primitive nebula with which the Solar System was formed, in the form of ice and dust, the same ones from which the planets and their respective moons later condensed.

What is its composition?

Comets are minor bodies in the Solar System made up of dry ice, water, ammonia, methane, iron, magnesium, sodium, and silicates, which orbit the sun following different elliptical, parabolic, or hyperbolic paths.

Due to the low temperatures of the places where they are found, these substances are frozen.

The dimensions to which a comet can measure are truly large, reaching several tens of kilometers.

Scientists think that within the materials that make up comets are organic materials that determine life, which after early impacts in the primitive solar system, especially on earth, could have given rise to living beings.

The cometary tail

All these components when approaching the sun are activated and what is called sublimation occurs, which is nothing more than the volatilization of the components of these.

In other words, it is a change from a solid to a gaseous state in a direct way without going through the liquid state. As a result of this process, the characteristic cometary tail appears in the comet.

Dirty ice balls

Fred L. Wipple was an astronomer who specialized in the study of comets and is considered the forerunner of cometary study.

Around the year 1950, Wipple was one of those who proposed that comets were “dirty balls of ice”, which was not totally wrong.

All the components of a comet, being far from the Sun, remain in a solid state, but due to their trajectory and as they get closer to the Sun, all these components volatilize through the sublimation process that has already been described.

These volatile elements of the comet are separated from the nucleus and are projected backwards, that is, in the opposite direction to the sun, due to the effects of the solar wind.

As this happens, comets sublimate materials as they approach the sun, fulfilling elliptical orbits and decreasing in magnitude.

After the comets have completed a certain number of orbits, it ends up being extinguished, and when the last susceptible materials are volatilized, the once comet will become a simple normal asteroid, because it will not be able to recover mass in that state.

Some examples of this can be found in asteroids 7968-Elst-Pizarro and 3553-Don Quixoteel, which were previously comets whose volatile materials were depleted.

Comets with variable orbits

There are comets whose orbit is long or very long, with a long or very long period that come from the hypothetical Oort cloud, and others that, due to their short-period orbit, come from the Edgeworth-Kuiper belt, located beyond the orbit. of Neptune.

One of the most famous comets is Halley’s Comet, which represents an exception to this rule since, although it has a short period of 76 years, it comes from the Oort cloud, which bears the name of the astronomer. Jan Hendrik Oort, composed of debris from the condensation of the nebula located between 50,000 and 100,000 AU from the Sun.

It should be noted that many of the comets that approach the Sun follow elliptical orbits so elongated that they only return after thousands of years.

Formation by aggregation and accumulation

The initial formation of cometary nuclei is explained by various models that determine that they were formed by aggregation and accumulation of materials.

Some of these models are:

  • Model developed by Fred Whipple, in 1950, called Whipple’s Ice Cream Conglomerate.
  • Littleton’s model, or Primitive Debris Accumulation, developed in 1948
  • Finally and more recently in 2004 the Ice and Silicate Aggregation Model in the protoplanetary disk, developed by Wednschilling.

Composition of comets by parts

To study the composition of comets, it is necessary to divide it into its three structural parts: the nucleus, the coma and the tail.

The nucleus

The nucleus is made up mostly of water and a conglomerate of ice, dust grains and carbon monoxide.

Once the nucleus has been heated by the sun, the ice becomes sublimated, which produces the release of the gas found in the dust grains.

The nucleus, in turn, is a solid body that has an irregular shape and whose density is normally low, and a size that ranges between 100 and 40 km.

They move thanks to the gravitational action offered by the sun, in addition to the other bodies that comprise the solar system, as well as by the reaction that is produced once the gas is expelled.

It has been detected, thanks to the investigations that have been carried out, that there is a great variety of compounds, both in the commas and in the tails.

Today it is known that the mostly volatile components in both parts of the comet are mainly water, followed by carbon dioxide, carbon monoxide, methanol, and other components such as methane, hydrogen sulfide and ammonia, in addition to pieces of other 60 different compounds.

The tail

Comet tails can present different variations in the form of filaments or shreds produced by the incidence of different interplanetary magnetic fields.

Sometimes such imperfections that are observed in the structure of the tails, or even the presence of emanations that come directly from the nucleus, are produced due to the very nature of the nucleus and the distribution of the materials that compose it.


The coma is made up of a nebula of dust and gas that sometimes presents certain bright structures such as jets, layers or fans.


  1. Pierson Barretto (2010) Comet’s Chemical Composition and Nuclei Structure. Recovered from sites.google.com
  2. Gemma Lavender, How are comets made? (2015) Recovered from spaceanswers.com
  3. Verónica Casanova (2014) Comets: complete guide. Structure and composition of comets. Recovered from astrofisicayfisica.com
  4. Comet (sf) In Wikipedia. Retrieved on July 7, 2017 from es.wikipedia.org
  5. Jose Vicente Díaz Martínez. (sf) The Comets: Definition and Classifications Recovered from josevicentediaz.com
  6. The Origin of Asteroids, Meteoroids, and Trans-Neptunian Objects (sf) Center for Scientific Creation. Recovered from creationscience.com

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