Dhristi JEE 2022-24

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 

  1. Usually, comets are known as “dirty snowballs” or “cosmic snowballs”. Because comets are made up of ice, rock, gas and dust.

  2. Comets generally take elliptical paths to move around the sun, like the planets. The path of a comet is more away from the planet.

  3. The nucleus of a comet has a huge variation in its total mass.

  4. 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. 

  5. Comets will generate ion tail, which is the result of solar wind that blows directly away from the sun. 

  6. In our solar system, there are billions of comets. And currently, the astronomers identified more than 3000 comets. 

  7. 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. 

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FAQs (Frequently Asked Questions)

Q1. How many comets are there?

Answer: As per astronomers, the reservoir of comet-like bodies in the outer solar system is more than one trillion. As of November 2021, astronomers have found about 4584 comets. But this is only a small fraction of the total potential comet population. 

Q2. Where is Halley's comet now?

Answer: Currently, the Halley comet is located slightly east close to the bright star Procyon. These Halley comets are visible in the night sky and are located in the direction of all other stars. It is mainly located in the Kuiper belt, which is in the outer solar system beyond the orbit of Neptune and Pluto.

Q3. How are comets made?

Answer: The comets in the solar system are mainly made of dusty snowballs and contains, carbon dioxide, ammonia, water, and methane. Usually, comets orbit around the sun and have a gas tail, which is created by the solar wind. The gas tail of comets started to develop straight back from the sun. 

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