Comets

what is a comet? Actually they are icy bodies which makes beautiful gas and dust tails when they passes near the Sun. Most commonly they are made of frozen water, gasses and dust particles. In other words they are kind of left overs at the making of solar system as asteroids.

There are so many interesting things to learn about comets. When these icy bodies float around the space they are just seems like normal asteroids but when Comets get closer to the Sun, the structure of the comets can be reveled. Before go deep in to more details about comets lets talk about the anatomy of the comets. 

 

Anatomy of a Comet (Image Credit: NASA/JPL-Caltech) [Link]

Mainly there are four things in the comet. The first thing is Nucleus or core of the comet. That is the only part of the comet which is pure solid in state. it is made of frozen water, rocks and dust particles.When the comet come closer to the sun, the heat of the Sun makes the icy nucleus sublimate. This sublimate process creates gases and these gases combined with dust particles and creates a visible atmosphere around the nucleus. And this is called the Coma of the comet. When this comet gets more near to the Sun, the ion tail will create. This ion or gas tail creates due to the charge particles in the solar wind. Also there is another tail called dust tail and this will creates due to radiation of the Sun. The ion tail is mostly blue in color while the dust tail is yellow in color. Ion or gas tail is directly points away from the Sun while dust tail also point away from the sun but has a little bit curvature. All these details that we talk about can be seen in this above diagram.

Comets usually have an elliptical orbit but some of the comets have parabolic or hyperbolic orbits. The short period comets are believed to be come from Kuiper belt and the long period comets are believed to be coming from Oort cloud.

 

Types of Orbits

 

In this below figure you can see how big is the Kuiper belt and the Oort cloud compared to the solar system. Oort cloud is the outer most region of the solar system and it is in the interstellar space.

 

Kuiper belt and Oort cloud (Image Credit: NASA) [Link]

There are so many comets that we have found. Some examples are Halley's comet, comet Hale-Bopp, comet ISON, comet NEOWISE and many more. The comets are widely researched by astronomers after the comet known as Halley's comet. This comet was named after Edmond Halley who lived during the period from 1656 to 1742.

 

Edmond Halley

 

Halley's comet is a periodic comet and he predicted this comet will return in 1758. This Halley's comet is about 11km across while Hale-Bopp comet is about 74km across. Following is the Halley's Comet.

 

 

Halley's Comet in 1986 (Image Credit: ESO) [Link]

Following is the Hale-Bopp Comet. In this image of the Hale-Bopp comet, you can see very clearly the ion tail in blue color and the dust tail in the yellow color. 

 

Hale-Bopp Comet (Image Credit: ESO/E. Slawik) [Link]

When we compare the size of these two comets, still there are larger comets than these two comets. In this image you can see the comet nucleus size comparison.

 

Comparison of Comet Nucleus sizes (Image and Illustration Credit: NASA, ESA, Zena Levy (STScI)) [Link]

Another interesting thing about the comets is, the Comet Shoemaker–Levy 9 which was broke apart in 1992 and collided with planet Jupiter in 1994. This comet fragments are about few hundred meters to 2km across and the original size of the nucleus was estimated about 5km. Although this comet was a very small compared to planet Jupiter, the collision fireball was bright enough to see from the Earth through the telescopes. This collision was lead astronomers to discover the secrets of the cloudy atmosphere of the Jupiter.

 

Comet Shoemaker-Levy 9 impacting with Jupiter in 1994 (Image Credits: ESO) [Link]

 

Another interesting thing about Comets is that it creates Meteoroid streams in the space across their orbit. Mostly these streams are made of dust and rock particles of the comet. When the Earth passes through one of these Meteoroid streams, Meteor showers can happen. These meteor showers are very colorful and these shooting stars are very exciting thing to see.

 

 

Meteoroid Streams in space (Image Credits: Self Evident Approach to Astronomy by Ashan Isuru Uyangoda)

 

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