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Comet Facts

Temperature is very irregular in outer space. The parts that are near stars are extremely hot! Think about Venus, the second closest planet to the Sun. It goes up to 462°C. But the background temperature in space is about -270°C – super cold! Things can change states if temperatures change so much. They can go from solid, to liquid, to gas! This is actually the reason why comets have their tails! 

An illustration of a very bright comet against the night sky.

The tail is one of the most distinctive features of a comet!

What is a Comet?

Before we learn about their tails, let’s figure out what comets are first! Comets are basically floating chunks of ice, dust, and frozen gases. Astronomers think that comets are the leftovers of planet formation. They believe that the dust and gases that didn’t become planets, became comets.
 
They’ve also nicknamed comets “dirty snowballs”! But that doesn’t mean that comets are only fist-sized. Some comets are easily larger than planets!

An image of a comet looking s,all in the night sky.

Comets may look small from a distance, but they’re actually gigantic!

Where do Comets come from? 

Comets come from either the Oort Cloud or the Kuiper Belt. The two are both areas packed with trillions of comets! There is an important difference between the two. The Kuiper belt lies inside our Solar System, and the Oort Cloud lies outside. So comets in the Kuiper belt have regular, oval orbits around the Sun. While comets in the Oort Cloud can get knocked off their paths by other things! Comets from the Oort Cloud are also long-period comets. This means that they can orbit the Solar System for much longer than Kuiper belt comets!

An illustration of the Solar System, showing the asteroid belt.

See how the Kuiper belt is disc-shaped? The Oort Cloud is farther away, so gravity from the planets don’t affect it as much. That’s why it envelopes the Solar System like a sphere or a cloud!

Parts of a Comet

Nucleus

Comets are made up of several parts. Comets first start off as only an icy or rocky nucleus – the center-most part of the comet. The nucleus is where most of the ingredients that make up a comet concentrate. So the nucleus is the heaviest and the smallest, most compact part of the comet! Comet nuclei are usually no more than 6 miles wide. 
 
Where the comet moves in space is important for its shape! When comets are still in the far reaches of the Oort Cloud or the Kuiper Belt, they’re made up only of their nuclei. But everything changes once they move closer to the Sun! Remember – a comet is mostly made out of ice.
 
And what happens to ice as it gets close to heat? It melts! In the case of comets, their nuclei start to sublimate, changing from ice to gas immediately. This is when the comet starts developing its other parts! 

Coma

As the ice melts, the comet gains a coma. The coma is basically a giant cloud of dust and different gases that surrounds the nucleus. Comas are extremely big – up to 600,000 miles across! The coma and the nucleus make up the head of the comet. A hydrogen cloud also develops around the comet’s head, but we can’t see it with our eyes. Hydrogen clouds are even bigger than comas – they can get as big as 10 Suns!
 
learn about comets

Here’s an easy way to remember what a comet’s head is called. The coma looks kind of like the head of a comma without its tail!

 

Tail

The comet also gets a tail – the part that we all know and love. There are two kinds of tails: a dust tail and an ion tail. The dust tail is made up of dust from the coma. Fun fact: dust tails always point away from the sun because of the pressure from solar winds! Dust tails are the easiest to spot from Earth. They’re several million miles long and reflect the Sun as well! The ion tail is made up of charged particles knocked off of the nucleus. Ion tails can stretch for hundreds of millions of miles! 

An illustration of a pretty comet with a long blue tail.

The comet’s tail appears when it gets close to the Sun. The tail is probably the most special feature of comets!

Comets Vs. Asteroids: Similarities and Differences

There is another important type of celestial object in the Kuiper belt: asteroids. Don’t get these two confused! They might sound similar, but they’re definitely not the same. If comets are space snowballs, then asteroids are cosmic rocks! Asteroids are all rocky materials and metals. Astronomers believe asteroids formed closer to the sun, so all the ice would have evaporated. Comets would have formed farther away, where ice could still be ice! 
 
a 3d ILLUSTRATION OF ASTEROIDS IN SPACE.

Asteroids are not icy like comets. Instead, they’re made out of rock and metals

Other Great Resources

Websites

NASA Goes In-Depth on Comets: https://solarsystem.nasa.gov/small-bodies/comets/in-depth/

Facts about ‘Dirty Snowballs:’ https://www.space.com/53-comets-formation-discovery-and-exploration.html

Comets and Comet History: http://nineplanets.org/comets.html

What are the Parts of a Comet?https://sciencing.com/parts-comet-8136471.html

 

Videos

Crash Course on Comets: https://www.youtube.com/watch?v=yB9HHyPpKds

An Animated Video on Comets: https://www.youtube.com/watch?v=-_6nYgel4JI

Even More About Comets: https://www.youtube.com/watch?v=mQErMYDfw0Y

 

Written by: Minh Nguyen