Why in news?

The recently discovered comet called C/2020 F3, also known as NEOWISE after the NASA telescope that discovered it, will make its closest approach to the Earth on July 22. On the day, the comet, which takes 6,800 years to complete one lap around its orbit, will be at a distance of 64 million miles or 103 million kilometers while crossing Earth’s outside orbit.

What are comets?

Comets are frozen leftovers from the formation of the solar system composed of dust, rock and ices. They range from a few miles to tens of miles wide, but as they orbit closer to the sun, they heat up and spew gases and dust into a glowing head that can be larger than a planet. This material forms a tail that stretches millions of miles.

There are likely billions of comets orbiting our Sun in the Kuiper Belt and even more distant Oort Cloud.

The current number of known comets is: 3,650

They are often compared to dirty snowballs, though recent research has led some scientists to call them snowy dirtballs.

Halley's Comet as photographed May 8, 1910, by Dr. G.W. Ritchey using the 60-inch (1.5-meter) telescope at Mount Wilson Observatory, Calif., during the comet's last appearance. The head of the comet and the beginning of its long tail are shown. Short, str

The word comet comes from the Latin word “Cometa” which means “long-haired” and the earliest known record of a comet sighting was made by an astrologer in 1059 BC.

Some comets, called sun-grazers, smash right into the sun or get so close that they break up and evaporate.

Structure of comets

The solid nucleus or core of a comet consists mostly of ice and dust coated with dark organic material,  with the ice composed mainly of frozen water but perhaps other frozen substances as well, such as ammonia, carbon dioxide, carbon monoxide and methane. The nucleus may have a small rocky core.

Naming  of comets

In general, comets are named after their discoverer. For example, comet Shoemaker-Levy 9 got its name because it was the ninth short-periodic comet discovered by Eugene and Carolyn Shoemaker and David Levy. Spacecraft have proven very effective at spotting comets as well, so the names of many comets incorporate the names of missions such as SOHO or WISE.

Why do comets get close to the sun?

Comets may be occasionally pushed into orbits closer to the sun and the Earth’s neighborhood due to forces of gravity of other planets.

The appearance of some comets, like those that take less than 200 years to orbit around the sun is predictable since they have passed by before.

These may be referred to as short-period comets and can be found in the Kuiper belt, where many comets orbit the sun in the realm of Pluto, occasionally getting pushed into orbits that bring them closer to the sun. One of the most famous short-period comets is called Halley’s Comet that reappears every 76 years. Halley’s will be sighted next in 2062.

The less-predictable comets can be found in the Oort cloud that is about 100,000 AU from the sun, or 100,000 times the distance between the Earth and the sun. Comets in this cloud can take as long as 30 million years to complete one rotation around the sun.

Why do astronomers study and track comets?

Astronomers study comets since they believe that they hold important clues about the formation of the solar system and it is possible that comets brought water and other organic compounds, which are the building blocks of life to Earth. Further, NASA tracks all Near Earth Objects (NEOs) that includes comets and asteroids using telescopes placed all around the Earth, as part of its NEO Observation Program.

This program has a congressionally directed objective to find, track and characterise NEOs that are 140 meters or larger in size since they can pose a risk to the Earth because of the devastation a potential impact can cause.

Visibility of a comet

Comets do not have light of their own and what humans are able to see from Earth is the reflection of the sun’s light off the comet as well as the energy released by the gas molecules after it is absorbed by the sun. The visibility of a comet cannot be precisely predicted since a lot depends on the way the “outbursts” of gas and dust play out determining how much of a “good show” the comet will put out for observers.