All through history, many civilizations observed comets and were both in awe and frightened by them. They didn’t know what they were and some thought that they were stars with “long hair” that would appear, possibly bringing bad news.
Due to being made up of mostly frozen methane, ammonia, and water, comets have been given the nickname of “dirty snowballs.” These celestial objects orbit the sun in an elliptical pattern, often going out into the reaches of cold space and then returning after a specific number of years to head to the sun.
It’s when the comet nears the sun that we can view them more easily because the sun heats of the comet contents and creates both the glow and the “tail” that we are familiar with.
As a comet nears the sun the ice inside of the comet begins to melt as well as the gasses that are found so that they glow. Comets actually have two “tails,” one that is for the gas or ion tail and the other as a dust tail.
The heat of the sun breaks down the basic structure of the comet and as it gets close to the sun the comet “sheds” parts of its contents. Because of this breakdown, scientists believe that comets have a limited life.
Scientists know that comets were leftovers from the early development of our solar system around 4.6 billion years ago.
Comets are made up of mostly ice that is coated with dark organic materials. It’s thought that comets may give us clues that are important in figuring out how our solar system was formed.
Scientists also believe that comets may have brought much or the organic compounds and water to the early Earth; both of which are considered by science to be the building blocks for life.
Basic Comet Statistics:
The scientific community calculates that there are around 3,576 known comets, with one occurrence visible from Earth every ten years.
When a comet is away from the sun it remains frozen and can be the size of a small town. As it nears the sun it heats up, spewing gases and dust into its head so that it glows larger than many of the visible planets.
The gas and dust will form a tail that stretches away from the sun for millions of miles.
It’s believed that there are billions of comets in orbit around the sun in the Kuiper Belt as well as even further in the Oort Cloud.
When a comet comes close to the Sun and their internal ices begin to melt, they have bright features that show.
There are 4 parts to these comets: the nucleus, coma, dust tail, and ion tail.
- The nucleus is the center most part of a comet that is made up of rocky materials and ice. A majority of the comets have a diameter of between 10-100 km, although some have reached 100 km in diameter.
- The coma is the gases that surround the nucleus. These are clouds of mixtures of ammonia, water vapor, and carbon dioxide.
- The dust tail is made up of tiny dust particles and gases that are blown away from the nucleus when it becomes heated. When we see a comet in the night sky, the most notable part of the comet is the bright wisp of the dust tail.
- The ion tail results from contact with the solar wind and is ionized gases that are streaming and blown away from the Sun.
In 1951, astronomer Gerard Kuiper had a theory that there was a kind of disc-shaped belt of icy objects that existed just past Neptune. He thought this population of dark comets orbited the sun in the area where we find the dwarf planet of Pluto.
His theory was that they existed in the realm but would sometimes be pushed by gravity into orbits that brought them closer to the sun. The name of this group was short-period comets. These are often the comets that can be predicted because their orbit takes less than 200 years and they have passed by Earth before.
The group known as long-term comets are not as easy to predict because they arrive from the Oort Cloud which is much farther away, around 100,000 astronomical units (AU) which is about 100,000 times the distance between the sun and the Earth. These long-term comets can take as long as 30 million years just to complete one orbital trip around the sun.
There are a few categories for comets, however, the most common are the non-periodic and the periodic. Past comets were simply named after the person that discovered them.
An Example of these include Sir Edmond Halley for Comet Halley. However, in more modern times comets have been given a set of governing rules by the IAU (International Astronomical Union).
A comet is given an official designation and it can also be identified by the last names of up to three independent individuals responsible for its discovery.
The basic guidelines of comet naming:
Once there has been a confirmed comet discovery, the naming rules are as follows:
If the comet is a periodic comet, then it’s indicated with a “P/” followed by the year of its discovery, a letter that indicates the half-month that it was discovered, then a number that shows the order of discovery.
An example of how this works would be if a comet was discovered in the first half of January, 2016, it would be called P/2016 A2.
If a comet is a non-periodic comet, then it’s indicated with a “C/” followed by the year of its discovery, a letter indicating the half-month that it was discovered, then a number that shows the order of discovery.
If three independent individuals discover a comet named Smith, Jones, and Johnson, it would be called Comet Smith-Jones-Johnson, in addition to the comet’s formal designation.
It’s a requirement today to use formal designations as many of the comets are located with automated instrument searches.
Most Well-Known Comets:
Comets have been studied by astronomers for thousands of years, and they have made note of those that make a reappearance after a specific amount of time. Some of those that are the most well-known include:
- Halley’s Comet: Discovered by Edmond Halley in 1705 when he was researching other comet orbits, Halley’s Comet is visible every 75-76 years. Although Edmond Halley is given credit for the discovery, Halley’s Comet was actually observed by a number of astronomers with reports that included the years of 1531, 1607, and 1682. It was Halley that decided that instead of being multiple comets, this was the same one returning in its orbit. This is the reason that the comet was named for Halley.
- Comet Shoemaker-Levy 9: This comet is also called SL 9 and was discovered as a string of comets in 1994 by Gene Shoemaker, Carolyn Shoemaker, and David Levy. It was famous as the comet that was snagged by Jupiter’s orbit and the world watched as the string of comets smashed into the surface of Jupiter. The collision left a series of dark spots on the planet that was studied and watched for many years.
- Comet Hale-Bobb: Named after the two astronomers that discovered it, Alan Hale and Thomas Bopp, the comet’s orbit is 2,300 years. The comet gained notoriety beyond the astronomical community when a California religious cult thought the comet was a spacecraft that was arriving to rescue them.
- 2001 NASA’s Deep Space 1 spacecraft flew by comet Borrelly: images were taken of the comet’s nucleus which is around 5 mi/8 km long.
- 2004 NASA’s Stardust Mission flew within 147 mi/236 km of the Comet Wild 2’s nucleus. The purpose of the mission was to collect cometary particles and interstellar dust using a special material. Photographs that were taken during the flyby of the nucleus of the comet showed jets of dust as well as a textured, rugged surface. The mission returned to Earth in 2006. Scientists analyzed the samples taken by Stardust and discovered that comets are a lot more complex than they originally thought. They found minerals that had been formed near the sun and other stars in the samples and this indicated that the materials from the solar system’s inner regions traveled to the outer regions to areas where the comets were formed.
- 2005 NASA’s Deep Impact mission was a flyby of a spacecraft that included an impactor. The impactor was released into the comet nucleus path of comet Tempel 1. The planned collision vaporized the impactor and ejected huge amounts of powdery, fine material that was located beneath the surface of the comet. On its way to impact, the camera took incredible images of the details of the comet. Two cameras and a spectrometer on the spacecraft recorded the impact and the data assisted scientists in understanding the composition and structure of the interior of the comet’s nucleus.
- Both the Stardust spacecraft and the Deep Impact spacecraft were in good condition after their missions and were retargeted for other comet flybys. Deep Impact’s mission was called EPOXI
- (Extrasolar Planet Observation and Deep Impact Extended Investigation) and was made up of two projects: (DIXI) the Deep Impact Extended Investigation, which encountered comet Hartley 2 in 2010, and (EPOCh) the Extrasolar Planet Observation and Characterization investigation, which was in search of Earth-size planets around other stars as it was headed to Hartley 2. In 2011 NASA came back to comet Tempel 1 when the (NExT) Stardust New Exploration of Tempel 1 mission observed any nucleus changes that occurred since Deep Impact’s 2005 encounter.
Facts about Comets for Kids:
- A comet’s nucleus is made up of ice and can be as tiny as a few meters across or as large as giant boulders that are a few kilometers across
- When a comet is at its closest point in orbit to the sun it’s called a “perihelion.” The farthest away from the sun in orbit is called the “aphelion.”
- Once a comet gets close to the sun the heat melts the ices and causes some of the ice to “sizzle.” Since there is no sound in space, this happens silently. Once the ice is close to the surface of the comet it can form a jet that looks something like a mini-geyser.
- There is a lot of material that streams off of a comet. If the material comes into content with Earth the particles fall and appear as meteor showers.
- As comets complete their orbits near the sun they lose some of their mass in a process called “sublimation.” This is why a comet has a limited lifespan. Eventually if a comet goes around the sun enough times it will break up.
- Thanks to scientific discoveries of what makes up a comet we now know that although they are made up of frozen water, and cold methane, ammonia, and carbon dioxide ices, we also know that they can contain a mixture of rocks, dust, and other bits of metallic materials from solar debris.
Comets have appeared throughout history in stories, legends, television, and film. Television has included comets in the TV series Avatar: The Last Airbender, the TV movie A Fire in the Sky,and in the series Friends with an episode where Ross Geller takes a group on a rooftop to view comet Bapstein-King.
A comet was featured as a main portion of the plot for the film Maximum Overdrive that involved radiation from a passing comet’s tail causing all of the Earth machines to come to life. Mighty Morphin Power Rangers: The Movie used Ryan’s comet to defeat an enemy.
The television series Millennium had a fictional comet with 2 tails called P197 Vansen-West. In the film Night of the Comet the entire Earth passed through a comet’s tail causing doom to all life except those that were enclosed in metal. Another fictional comet called Yano-Moore was created for the BBC series Space Odyssey: Voyage To The Planets.
In two episodes of Star Trek: Enterprise comets played important roles. In the television series The Simpsons, Bart discovers that a comet is going to collide with Springfield.
The fictional world of Myth features a transition from the age of light into darkness that is preceded by the sight of a comet.
Shadow the Hedgehog game has a special comet that keeps the games main enemies at bay.
Super Mario Galaxy game has a character Rosalina, that uses a building that looks like a comet to travel through the universe. In the world of Warhammer Fantasy Roleplay the character Sigmar has a twin-tailed comet.