Since time immemorial Comets have played on the feelings of humans. They were considered to be an ill omen to oncoming disastrous events. The oldest mention of a Comet was made in the Epic of Gilgamesh which is the oldest written epic in the world. This was written down on tablets way back in 1600 BC in the Akkadian language.
It is better to look at Comets scientifically as astronomical bodies ignoring those myths.
However, before knowing about Comets we also have to know what are Kuiper Belt & Oort Cloud.
KUIPER BELT: An imaginary disc in the outer solar system originating from the orbit of Neptune from 20 AU (AU-Astronomical Unit-Distance from Earth to Sun 147 million KM) away and stretches up to 50 AU in space.
Like the Asteroid belt it contains remnants from the formation of the solar system 4.6 billion years ago and is composed of frozen methane, ammonia and water. This is also home to the dwarf planets: Orcus, Pluto (now classified as a dwarf planet), Haumea, Quaoar and Makemake.
More than 100,000 Kuiper belt objects with over 100 Km diameter are supposed to exist.
OORT CLOUD: This is different from the Kuiper belt and it stretches from 2000 AU from the earth to 200,000 AU.
The collective objects from the Kuiper belt and the Oort Cloud are known as Trans Neptunian Objects or TNO’s.
Comets are bodies of icy frozen gases, rocks and dust left over from the formation of the Solar System 4.6 billion years ago. They orbit the Sun in highly elliptical orbits that in some cases take hundreds of thousands of years to complete.
As a comet approaches the Sun it heats up to turn the ice into water vapor, carbon monoxide, carbon dioxide and other trace substances which become visible to us as the Comets tail. While some comets contain more ice, others contain more dust.
As of now the number of known comets is 3743 although billions of them may be orbiting the Sun beyond Neptune in the Kuiper Belt & the Oort Cloud.
A comet consists of a Nucleus, coma, hydrogen envelope, dust and plasma tails. As the Comet approaches the Sun it gets heated up by the solar winds and a part of the frozen gases melt and form its tail. In some Comets the tails only consist of dust. The tail always points away from the sun due to the Solar winds.
We can see a number of comets with the naked eye but most of them are small and have to be viewed through telescopes. Comets leave a trail of debris along their paths and may lead to meteor showers on Earth.
Comets are classified according to the duration of their orbits around the Sun.
Short period comets complete one orbit in 200 years or less. Long period comets take more than 200 years.
There are some comets that are not bound to the sun and their orbits take them out of the solar system. They are called single apparition comets.
Scientists believe that short period comets originate from the Kuiper belt and the long period comets come in from the Oort cloud.
Some Comets known as sun grazers smash right into the sun or get so close that they breakup and evaporate. Some researchers believe such comets may pose a threat to the earth as well.
Comets are generally named after their discoverers.
The Halleys comet is the most famous in the world. It becomes visible to the naked eye every 75 years. It last flew near the earth in 1986. The Halleys comet is only 15 Km long.
In 1994, the comet Shoemaker Levy collided with Jupiter with Jupiter's pull ripping it apart resulting in 21 visible impacts.
The largest collision among them created a fireball that rose 3000 Km above Jupiter's cloud tops. It exploded with a force of 6000 giga tons of TNT.
In 1997, the comet Hale-Bop came to 197 million Km from the earth and was about 30-40 Km across.
In 2021 scientists have discovered the largest comet ever seen known as Bernadinelli-Bernstein. The comet is about 100 to 200 Km across. This would make its closest approach to the earth in 2031 but would still pass at a great distance.
