Comets are space objects composed primarily of rocks, ice, and dust. They orbit the Sun and, along with asteroids , planets, and their satellites, form part of the solar system. For example:Halley’s comets, Shoemaker-Levy 9, 3D/Biela.
A characteristic of comets is their visible tail. This is a trail formed by gases produced when a comet approaches the Sun, as its surface heats up, causing the ice to turn into gas.
Comets are thought to originate primarily from two groups of celestial objects:
- The Oort Cloud. Located at a distance from the Sun of between 50,000 and 100,000 AU (astronomical units). It is composed of icy and rocky debris left over from the formation of the Solar System.
- The Kuiper Belt. It lies beyond the orbit of the planet Neptune. Comets in the Kuiper Belt are affected by the gravity of Neptune and other outer planets, which can disrupt their orbits and send them into the inner solar system.
Astronomical unit (AU) : An astronomical unit is equal to the distance between the Earth and the Sun, approximately 149 million kilometers.
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Types of kites
There are three main ways to classify comets: by their origin, by their size, and by their orbit.
- Comets according to their origin and spatial trajectory. Long-period comets, which originate from further away and originate in the Oort Cloud, are distinguished from short-period comets, which originate in the Kuiper Belt.
- Comets by size. They are classified as dwarf (0 to 1.5 km in diameter), small (1.5 to 3 km), medium (3 to 6 km), large (6 to 10 km), giant (10 to 50 km), and Goliath comets (more than 50 km in diameter).
- Comets according to their orbital period. Short-period comets are distinguished, if they complete one orbit in less than 200 years (for example, Halley’s Comet, which takes 76 years), and long-period comets, if they take more than 200 years to complete the orbit.
Naming comets : Astronomers have developed a specific nomenclature for comets. Those with the letter P in their name mean that they are comets with a periodic orbit, returning to the solar system with a certain regularity. The letter C indicates that they are non-periodic comets, which do not maintain a regularity. The letter D indicates that they are deceased comets, which means that they were observed at some point but have since been destroyed.
Examples of comets
Halley’s Comet is the most famous in existence.
- Halley’s Comet
It is the most famous comet in existence. It has an orbital period of about 76 years and is one of the brightest comets from the Oort Cloud. It is, in fact, the only short-period comet visible to the naked eye from Earth. It has been observed since ancient times, having been first sighted in 240 BC. It was last seen in 1986 and is expected to be observed again in 2061.
- The Great Comet of 1577
Officially named C/1577 V1, this comet passed close to Earth in 1577 and was observed by many European astronomers, including the Danish astronomer Tycho Brahe. It was one of the first comets to be studied with astronomical instruments, and its appearance was very important at the time for understanding the nature of comets.
- The Great Comet of 1811
Officially named C/1811 F1, this comet could be seen with the naked eye for 260 continuous days, given its spectacular size and 40 km in diameter. Its orbital period is estimated to be 3,065 years. Its brightness was comparable to that of the full Moon.
- 19P/Borrelly
It was discovered by Alphonse Borrelly in 1904. Its orbital period is 2,484 days. In 2001, it was visited by the Deep Space 1 space probe, which took photographs and obtained data on its composition and nucleus.
- Hale-Bopp Comet
Also known as the Great Comet of 1997 or C/1995 O1, it is probably one of the most observed comets of the 20th century and one of the brightest ever seen. It was discovered simultaneously by Alan Hale and Thomas Bopp in 1995. It was visible to the naked eye for several months.
- 67P/Churyumov-Gerasimenko
It was discovered in 1969 by Ukrainian scientist Klim Ivanovich Churyumov thanks to the studies of scientist Svetlana Gerasimenko. It has an orbital period of 6.6 years and was, in March 2004, the destination of the European space mission Rosetta. This space probe was able to approach the comet’s body, take photographs, and measure its magnetic field.
- 3D/Connecting Rod
It was spotted in 1772 and 1805, but it wasn’t until 1826 that the German astronomer Wilhelm von Biela was able to calculate its orbit. In 1845, it was observed fragmented in two, and in 1877, when it was supposed to pass by again, it didn’t. Instead, a meteor shower lasting almost six hours was observed in the constellation of Andromeda. It is presumed to have disintegrated, because it was never seen again.
- Shoemaker-Levy 9
This comet, discovered in 1993 and formally named D/1993 F2, was a major event in 1994 when it hurtled toward Jupiter and crashed into it. The event sparked profound interest in astronomy worldwide, as it was the first observable impact of a cosmic body on a planet’s atmosphere.
- 9P/Tempel 1
It was discovered in 1867 by German astronomer Wilhelm Tempel. In 2005, it was studied by NASA’s Deep Impact space probe, which fired a projectile at the comet to analyze its nucleus.
- Hyakutake
Officially named C/1996 B2, it was discovered by Japanese astronomer Yuji Hyakutake in January 1996. It was one of the brightest comets of the 20th century. It passed very close to Earth and was visible to the naked eye.
