Comets

A comet is a small body in space. Comets were a subject of great interest to astronomers like Sir Edmond Halley. Many decades later, comets still remain a challenging mystery in the field of astronomy. Space research institutes around the world have reportedly discovered the existence of 3628 comets.

As per the definitions given by various space research organizations, a comet can be defined as a space body that travels in an elliptical orbit around the sun. Most of the comets travel in elliptical orbits. When a comet comes in the vicinity of the star it orbits around, its comma-like tail gets illuminated. Most comets are visible only through high power telescopes and other aids. However, there are some comets which are also visible to the naked eye.

A comet is basically made up of ice, dust and different forms of gases. The nature of the components differs from comet to comet. The core of a comet that looks like a ball is called the nucleus. The nucleus is principally made up of ice and frozen gases. The frozen components include many other compounds such as ammonia, methane and carbon dioxide. Rocks are another component of the nucleus. Due to its composition, the nucleus of a comet often resembles a huge ball of dirt and snow.

Some astronomers believe that the nucleus of a comet is rather fragile because several comets have split into parts without any explainable reason except immense velocity.

The huge elliptical orbit takes the comet close to the star around which it is orbiting. When the comet enters the inner regions of the solar system, the frozen content of the nucleus starts melting. The gases and water inside the nucleus vaporize as a result of radiation from the star and the solar wind. The immense velocity of the comet along with the solar wind, push the vaporized matter away from the nucleus. This gives the comet it's distinct tail and a comma-like appearance. The high amount of heat and the ionic particles (charged particles that are formed due to the heat of the sun) cause the tail of the comet to glow.

Based on their formation or birth, the comets can be classified into two types. The first type called short-term comet originate in the Kuiper belt beyond the orbit of Pluto. The gravitational pull of the planets in the solar system leads to the formation of short term comets. These comets enter the solar system and take the form of active and glowing comets.

Long term comets originate as traveling bodies or objects in the Oort cloud (located around 50,000 light years away from the sun). The gravitational attraction of the planets and other gravitational forces cause these comets to form elliptical orbits.

The study of comets has revealed that they possess a fragile structure. Sometimes, comets split into parts due to sheer velocity. When a comet enters and exits the solar system in course of its orbit, the amount of matter (ice and frozen gases) in it reduces. Due to this reduction in matter, the comets split-up and disperse into clouds. A dead comet is nothing but an asteroid. Sometimes comets crash into planets when their orbits cross each other. The most famous example of such an incident is when a comet called Shoemaker Levy crashed into Jupiter. The Halley's Comet will be visible every 76 years. It was last seen in 1986 and is a very special comet. Another very beautiful comet is the Hale-Bopp, which was discovered in the year 1995, on 23rd July.

Questions to Ponder

• What caused Shoemaker-Levy 9 to split up?
• When will Hale-Bopp return?
• How do comets survive, when so much of their mass is reduced when they come close to the sun?