Comets: The Cosmic Wanderers
By Siri Paramesh
Cosmofluencer (Season 2)
Introduction
Comets have intrigued humanity for centuries, igniting our curiosity about the vast and mysterious cosmos. These celestial wanderers, often described as “icy dirtballs,” have played a significant role in shaping our understanding of the universe. In this blog post, we will delve into the captivating world of comets, exploring their origins, composition, and the mesmerising tails that make them visible to the naked eye.
What are Comets?
Comets are icy bodies composed of water, ice, frozen gases, dust, and rocky material that orbit the Sun. Unlike planets, comets have highly eccentric and elongated orbits, which means they spend most of their time in the distant reaches of the solar system. They have a wide range of orbital periods, ranging from several years to potentially several millions of years. Short-period comets originate in the Kuiper belt or its associated scattered disc, which lie beyond the orbit of Neptune. Long-period comets are thought to originate in the Oort cloud, a spherical cloud of icy bodies extending from outside the Kuiper belt to halfway to the nearest star.
In short, comets are frozen leftovers from the formation of the solar system composed of dust, rock, and ice. 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.
The gravity of a star pulls the comets from their homes in the Kuiper Belt or Oort Cloud. This force can redirect a comet toward the Sun. The paths of these redirected comets look like long, stretched ovals. As the comet is pulled toward the Sun at increasing speeds, it swings around the Sun and then heads back toward where it came from. Some comets dive right into the Sun, never to be seen again. It is during this time, when the comet is in the inner solar system, that we get to witness its blazing glory in our skies.
Composition and Structure
Comets include water ice, methane, ammonia, carbon dioxide, and various organic compounds. The nucleus, the solid core of a comet, is typically a few kilometres in diameter and is surrounded by a cloud of gas and dust known as the coma.
The surface of the nucleus is generally dry, dusty or rocky, suggesting that the ice is hidden beneath a surface crust several metres thick. The nuclei contain a variety of organic compounds like acetaldehyde, ethylene glycol, formamide, methyl formate, ethanol, etc.
The streams of dust and gas thus released form a huge and extremely thin atmosphere around the comet called the “coma”. The force exerted on the coma by the Sun’s radiation pressure and solar wind causes an enormous “tail” to form pointing away from the Sun.
The Orbit of the Comet and Its Tail
A Comet’s tail is its most spell-binding and distinctive feature. There are two types of tails: the ion tail and the dust tail.
The ion tail is composed of ionized gases, such as carbon monoxide and nitrogen, and is typically bluish. The dust tail is made up of microscopic particles and reflects sunlight, appearing white or yellow. The orientation of these tails is determined by the solar wind and the comet’s position in its orbit.
Famous Comets through History
Throughout history, certain comets have left an indelible mark on human consciousness. One of the most famous comets is Halley’s Comet, which visits the inner solar system roughly once every 76 years. Its appearances have been documented for centuries, and it has been a source of both awe and fear. Other notable comets include Comet Hale-Bopp, which graced the skies in 1997, and Comet NEOWISE, which made a spectacular appearance in 2020.
Halley’s Comet
Halley is often called the most famous comet because it marked the first-time astronomers understood comets could be repeat visitors to our night skies. Astronomers have now linked the comet’s appearance to observations dating back more than 2,000 years. Halley was last seen in Earth’s skies in 1986 and was met in space by an international fleet of spacecraft. It will return in 2061 on its regular 76-year journey around the Sun.
Comet 2I/Borisov
Comet 2I/Borisov is the first confirmed interstellar comet. It was discovered by Crimean amateur astronomer Gennady Borisov on Aug. 30, 2019, and quickly became a global phenomenon. Comet 2I/Borisov formed in a different star system than our Sun and its family of planets.
Comets are invaluable to scientists as they provide insights into the early solar system. The pristine ices and organic materials within comets are like time capsules, preserving the conditions and building blocks that existed when the solar system formed over 4.6 billion years ago. Space missions, such as the European Space Agency’s Rosetta mission, have allowed researchers to study comets up close, shedding light on the secrets of our cosmic origins.
Conclusion
Due to their ethereal beauty and enigmatic nature, comets continue to capture our imagination and fuel our quest for understanding the universe. As we gaze at these celestial wanderers with their glowing tails, we are reminded of the ever-changing and dynamic nature of the cosmos, where even the most distant and icy objects can hold the key to unraveling the mysteries of our existence.