What is a Comet?
The word comet is derived from the Greek word kometes, which means long-haired. A small body that is composed of volatile ices and dust particles that are orbiting around the sun is known as a comet. While a comet reaches close to the sun, the ices in comets get sublimate and completely became dust particles. Later, the comets get illuminated and a brighter outflowing atmosphere around the comet nucleus is known as the coma. The dust and gas particles in the coma flow freely into the space and form two tails. One tail of the coma contains molecules and radicals and another tail contains dust particles.
This article explains the origin of comets, structure, parts of comets with composition and facts of comets in detail.
Origin of Comets
Comets are the most spectacular object in the sky. Because they have bright glowing comae and long dust tails and ion tails. Usually, comets in the solar system travel in highly eccentric orbits around the sun in their own orbit. Usually, the motion of the comets is dominated by the gravity of the sun or the gravity of planets in the solar system.
Many scientists researched on comets and found that the comets are the primitive leftover bodies during the period of formation of the solar system. They considered that comets should be the first solid bodies that are formed in solar nebule. Usually, the solar radiations formed in the universe disturb the comets in their orbit. Most of the comets are located 6 astronomical units away from the orbit of Jupiter. And also, most of the comets are located in the distant orbit beyond the planets. Sometimes these comets will undergo physical changes like melting due to the modifications in the solar system. The physical and chemical modified records of the comets have also remained in the solar nebula.
Parts of a Comet
The comets in the solar system are mainly composed of four visible parts. These parts of a comet describe the structure of a comet. They are the coma, the nucleus, the ion tail and the dust tail.
The nucleus of the comets is a solid body that is located a few kilometres in diameter. They are mainly composed of a mixture of volatile ices (predominantly water ice) and silicate and organic dust particles.
The coma in the comets is found around the nucleus, and can freely escape to the atmosphere, while the comets contact close to the sun. During that time, the volatile ices sublimate, carrying with them dust particles that are intimately mixed with the frozen ices in the nucleus.
The dust tails in the comets are formed by the dust particles when the comets are blown back by solar radiation pressure. Further, it forms a long curving tail that appears white or yellow in colour.
The ion tail in the comets is formed by the volatile gases in the coma. Usually, they get ionized by the ultraviolet photons from the Sun and blown away by the solar wind. Usually, the ion tail of the comets will face exactly away from the sun and shine in bluish colour. The comets are made up of CO+ ions.
Orbits of Comets
Usually, the comets are different from other bodies in the solar system. Comets also orbit around the sun, which is far more eccentric than the planets and other asteroids. Sometimes, comets will come to a distance of about 50,000 AU, which is a substantial fraction of the distance to the nearest stars. The orbital period of the comets will vary from a few years to millions of years depending on the length of the orbit. The comets with a shorter orbital period will carry the comets inwards of the terrestrial planets like Jupiter and Saturn. Some comets will also contact the interstellar space and passes around the sun on open hyperbolic orbits.
Composition and Facts of Comets
Comets in the universe have abandoned water, carbonaceous molecules (CO, CO2, and hydrocarbons) and silicates. All the compositions are available in the ratio of about 1:1:1. They also contain other ions and dust particles. The core of the comets are made up of an amalgamation of rock, dust, water ice, and frozen carbon dioxide, carbon monoxide, methane, and ammonia. In order to study the appearance of comets, the IAU has implemented new identification methods in 1995. Through this method, it is possible to identify, whether the comets are short periodic orbital or long-period comets. The identification system is much similar to the identification of asteroids.
Neowise Comet
The neowise comet is one of the long-period comets, which has a nearly parabolic orbit. This neowise comet was discovered on 27th March 2020 during the Neowise mission of the Wide-field Infrared Survey Explorer (WISE) space telescope. This comet was located about 2 AU away from the sun and 1.7 Astronomical units away from the Earth. The neowise comet is the brightest comet in the solar system.
Interesting Comets Facts
Usually, comets are known as “dirty snowballs” or “cosmic snowballs”. Because comets are made up of ice, rock, gas and dust.
Comets generally take elliptical paths to move around the sun, like the planets. The path of a comet is more away from the planet.
The nucleus of a comet has a huge variation in its total mass.
When comets are moving around the sun, it has a halo. The solar radiation vaporizes the ice and gas. This halo is known as the comet coma.
Comets will generate ion tail, which is the result of solar wind that blows directly away from the sun.
In our solar system, there are billions of comets. And currently, the astronomers identified more than 3000 comets.
It is possible to view comets in the naked eyes of Earth without the telescope.
This article explained what is a comet, the origin, parts of the space comets, composition and facts of comets and the purpose of a comet in detail.
FAQs on Comet
1. What is a comet and why is it sometimes called a 'dirty snowball'?
A comet is a small celestial body made of ice, dust, and rock that orbits the Sun. The nickname 'dirty snowball' comes from its composition: a core (nucleus) of frozen gases and water ice (the 'snow') mixed with rock and dust particles (the 'dirt'). As it nears the Sun, the ice turns to gas, creating a glowing atmosphere and tail, which makes it visible.
2. What are the four main parts of a comet?
An active comet typically consists of four distinct parts that become visible as it approaches the Sun:
- Nucleus: The solid, stable core made of ice, gas, and rock.
- Coma: A large, glowing cloud of gas and dust that forms around the nucleus as it heats up.
- Dust Tail: A broad, curved tail formed by dust particles pushed away by the pressure of sunlight. It is often yellowish or white.
- Ion Tail: A tail made of ionised gas from the coma, pushed directly away from the Sun by the solar wind. It often glows blue.
3. What is the main difference between a comet and an asteroid?
The main difference between a comet and an asteroid is their composition and orbit. Comets are made of ice, dust, and rock, which vaporise to form a tail near the Sun. Asteroids are primarily made of rock and metal and do not form tails. Furthermore, comets typically have highly elliptical or elongated orbits, while asteroids usually have more circular orbits, mostly found in the asteroid belt.
4. Why do comets have tails, and why are there two different types?
Comets develop tails only when they get close to the Sun. The Sun's heat causes the comet's icy nucleus to sublimate, releasing gas and dust that form a large coma. Two different forces from the Sun then act on this material to create two distinct tails:
- The Ion (Gas) Tail is created when the solar wind pushes charged gas particles directly away from the Sun.
- The Dust Tail is formed when solar radiation pressure pushes the heavier dust particles. This tail is often curved and follows the comet's orbital path.
5. How does a comet's orbit differ from a planet's orbit?
A comet's orbit is fundamentally different from a planet's. Planets have nearly circular orbits that lie on a similar flat plane. In contrast, comets have highly eccentric (elongated, oval-shaped) orbits. This eccentric path takes them from the frigid outer solar system very close to the Sun and then back out again, resulting in orbital periods that can range from a few years to millions of years.
6. Why are comets considered important for studying the early solar system?
Comets are considered cosmic time capsules because they are primitive leftovers from the formation of our solar system over 4.6 billion years ago. Since they have spent most of their existence in the deep freeze of the outer solar system (like the Oort Cloud), their composition has remained largely unchanged. Studying them provides direct clues about the original chemical and physical conditions of the solar nebula from which the Sun and planets were formed.
7. Can comets be seen from Earth without a telescope?
Yes, but it is a rare occurrence. Some comets, like Comet NEOWISE in 2020 or Halley's Comet on its periodic returns, can become bright enough to be seen from Earth with the naked eye. For this to happen, the comet must be sufficiently large and its orbit must bring it close enough to both the Sun (to become bright) and Earth (to appear large in our sky).
8. Where is Halley's Comet right now?
As of 2025-26, Halley's Comet is journeying through the outer solar system, having passed its farthest point from the Sun in late 2023. It is currently located far beyond the orbit of Neptune and is extremely faint, making it impossible to see without powerful professional telescopes. It is on its long path back toward the inner solar system and is expected to become visible from Earth again around the year 2061.
