The composition of comets makes them especially interesting and unique. Unlike asteroids, which are made up primarily of rock-like material with ice on the side (making them a “dirty snowball”), comets contain only small amounts of rocky materials while being mostly composed of out ices or frozen gasses like ammonia, methane, or water vapor – making these celestial bodies nicknamed as “clean snowballs.”
Facts About Comets
- Comets are often called “dirty snowballs” or “cosmic snowballs”.
- Comets are small, orbiting objects that travel in elliptical paths just like the planets.
- A comet is made up of four components.
- A comet’s nucleus is huge! It contains 90% of the total mass.
- When a comet moves close to the Sun and becomes surrounded by its halo.
- When the comet is closest to the sun, it’s called perihelion.
- The ion tail of a comet is the result of solar winds.
- It’s rare to see a comet orbit that isn’t an ellipse.
- Comets are believed to originate from the Oort Cloud and the Kuiper Belt.
- The most famous comet is Halley’s Comet which can only be seen every 75 years.
- There are over 3,000 comets whizzing through the solar system.
What is a Comet?
A comet is a ball of ice, dust, and rock that orbits the sun. Most comets are no larger than 10 kilometers across but their main body called the nucleus can contain water, methane, nitrogen, and other ices as well!
The dust tail is what we normally see when viewing comets from Earth. When a comet has been heated by the sun, its ices begin to sublimate and this mixture of ice crystals and dust blows away from the nucleus in solar winds creating two tails. One made up of gas molecules that form an ionized plasma trail (the other consisting mainly out of gas)
The wonderful colors in the sky from a comet are due to its plasma tail. Comets typically orbit the Sun, and have origins that lie either within The Oort Cloud or Kuiper Belt regions of our outer solar system both still largely unexplored by humans!
Parts of A Comet
As the bright and icy comet nears the sun, they will melt into a series of changing features that can be seen from Earth. These features are as followed:
Nucleus: The nucleus of a comet sometimes has the power to cause destruction. It is made up of ice and rock that can be as large or small as 100 kilometers in diameter with most being within 10-100 km in size.
Coma: The coma is a cloud of gases that forms around the nucleus as it heats up. These gas are usually made from water vapor, ammonia, and carbon dioxide.
Dust Tail: Comets are known for their spectacular tails. These dust trails come from the nucleus of a comet as it is heated up by the sun and streams away in space, giving off light.
Ion Tail: The ion tail is a stream of ions that are pushed away from the Sun because it meets with the solar wind.
Where Do Comets Come From?
Humans have been witnessing to comets for millennia. But, scientists have determined that as the comet orbits closer and farther from the sun repeatedly they shed material which limits their lifespan to only a few thousand years in comparison with the life of our solar system.
Scientists have found that if comets are still present in the Solar System, there must be a nursery of them somewhere out there. Otherwise, all the comets would have run their course long ago.
Furthermore, the only place left for this reservoir of new comets to exist is in the outer Solar System.
The comet’s orbits have led scientists to believe that there are not just one, but two regions of the outer Solar System producing comets.
The Kuiper Belt is the first region that is a band of comets that orbit the Sun in much the same way as do planets. They can be distinguished from asteroids because they have relatively short orbital periods and travel around our star on roughly the same plane.
This second region, called the Oort Cloud is one of many mysterious regions on our planet. The comets coming from this area have orbital periods.
Much longer than those of the Kuiper Belt and their orbit may be drastically inclined to that of planets due to being located beyond Pluto’s orbit in a spherical shell formation outside Neptune and Uranus’ orbits.
Comets originating in the outer Solar System are typically only visible near their closest approach to Earth.
Any comet that has an orbit that takes it into the inner solar system must have had its trajectory altered for some reason, either from a collision with another comet or by the gravitational pull of an interstellar object passing nearby.
Comets come in several categories with the most common being periodic and non-periodic.
You may have heard of some comets in your lifetime. This is because historically they were named for the people who discovered them. Such as Halley’s comet after Sir Edmond Halley and Comet Hyakutake which was first observed by a Japanese observer.
Today, though their naming process has changed to one set out by the International Astronomical Union (IAU). A comet’s designation is unique to it. It can also be identified by the last names of up to three discoverers.
Every once in a while, space rocks (comet) with near-earth orbits are discovered. These comets can be named under the following rules:
A periodic comet is indicated by a P/ followed by the year of its discovery. A letter indicating the half-month in which it was discovered. Then finally a number that indicates when they were found.
For example, the sixth comet discovered in February 2021 would be called P/2021 B6.
There are some famous comets, with a few being well-known to ancient humans and others only appearing recently. Below is the most popular list of all time.
Halley’s Comet: Halley’s comet has been seen every 75-76 years since it was first identified in 1705. Studying the orbits of these comets, Edmond Halley found that the 1607 and 1682 sightings were one and the same as well; this led to his name being forever attached to our favorite celestial friend!
Comet Hale-Bopp: Comet Hale-Bopp is a comet that was last seen in 1997. If you were born before then, it might be your only chance to see this amazing phenomenon. It was named after its co-discoverers and looks like the end of time when viewed from Earth’s perspective because we can’t predict what will happen if/when it returns 2,300 years later. But let’s hope for something beautiful!
Comet Shoemaker-Levy 9: Shoemaker-Levy 9 was a string of comets, and some believed it to be an alien spaceship. However, the orbit took on about Jupiter in 1994 due to its irregularity. When Shoemake saw this he became excited with how strange it would look from Earth. If they were close enough for us to see them as large discs around each other rather than point sources across our sky. Like two giant cosmic jellyfish swimming through space together!