What Is a Comet? — For Kids
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What Is a Comet? — Elementary
The short answer
A comet is made of dirty ice, dust, and gas.
It orbits the Sun.
To orbit means to go around and around.
When a comet gets close to the Sun, it grows a long tail.
Left over from long ago
Scientists believe comets are made of material left over from when the Sun and the planets were formed.
They think that about 100,000 million comets orbit the Sun.
That is a lot of comets!
A trip close, then far away
Some comets orbit the Sun like planets.
Their orbits take them very close to the Sun.
Their orbits also take them very far away from the Sun.
What happens near the Sun?
When a comet gets close to the Sun, part of the ice starts to melt.
The melting ice lets out dust and gas.
The solar winds then push that dust and gas away from the comet.
That push forms the comet’s tail.
A long tail with very little in it
A comet’s tail can be millions of kilometers long.
But the tail holds very, very little matter.
All the matter in the tail could be held in a large bookbag.
A tail can look big and hold almost nothing!
A comet makes no light of its own
A comet does not give off any light of its own.
What looks like light from the comet is really a reflection of our Sun’s light.
Sunlight bounces off the comet’s ice.
It bounces in the same way light is reflected by a mirror.
So if comets have no light of their own, how can we see them?
We see the sunlight that bounces off them.
Melting a little bit at a time
Every time a comet comes close to the Sun, a part of it melts.
Over time, the comet will completely disappear.
Each trip near the Sun makes it a little bit smaller.
Comets we can see
A few comets come close enough to Earth for us to see them with our eyes.
Halley’s Comet is one of them.
Halley’s Comet can be seen from Earth every 76 years.
Words to know
- Comet
- An object made of dirty ice, dust, and gas. It orbits the Sun, and it grows a tail when it gets close to the Sun.
- Tail
- The long part that forms behind a comet near the Sun. Solar winds push dust and gas away from the comet, and that forms the tail. A tail can be millions of kilometers long.
- Orbit
- The path an object follows as it goes around the Sun. A comet’s orbit takes it very close to the Sun and very far away from the Sun.
- Solar wind
- The wind from the Sun. Solar winds push the dust and gas released by a comet’s melting ice away from the comet.
What Is a Comet? — Middle
The short answer
A comet is a body made of dirty ice, dust, and gas that orbits the Sun.
Far from the Sun, a frozen comet is basically invisible.
Near the Sun, part of its ice melts, it grows a cloud called a coma, and solar winds push released dust and gas out into one or two long tails.
Leftover material, in huge numbers
Scientists believe that comets are made up of material left over from when the Sun and the planets were formed.
They think that about 100,000 million comets orbit the Sun.
Some comets orbit the Sun like planets, and their orbits take them very close to and very far away from the Sun.
As a comet travels in its orbit, sometimes it gets close enough to the Sun to warm up enough so that the ice begins to evaporate.
That releases the trapped materials — the dust, gas, and such — into space.
The parts of a comet: nucleus and coma
At such times, comets have several distinct parts.
The nucleus is the solid core of the comet. It is mostly ice and gas, with a small amount of dust and other solids.
The coma is a dense cloud spewed off by the evaporating nucleus as the comet nears the Sun.
When the nucleus is frozen, it can be seen only by reflected sunlight — so comets are basically invisible.
When they are near the Sun, however, a coma develops and everything changes.
The comet starts to look like a big “fuzzy ball.”
Coma material is then blown away from the coma by the solar wind, and that becomes the comet’s tail.
Two tails, both enormous and both thin
A comet can have a dust tail up to 10 million km long. The dust tail is the part of a comet we see.
A comet can also have an ion tail up to 100 million km long.
Comet tails can stream out up to 100 million km in length, yet the amount of material in a tail is not very large.
A tail can be millions of kilometers long, but the amount of matter it contains can be held in a large bookbag.
Because the tails hold so little material, spacecraft have flown through the tail of a comet.
Reflected light, like a mirror
A comet does not give off any light of its own.
What seems to be light from the comet is actually a reflection of our Sun’s light.
Sunlight bounces off the comet’s ice particles in the same way light is reflected by a mirror.
That reflected sunlight is how we are able to see a comet at all.
A little smaller on every visit
Every time a comet comes close to the Sun, a part of it melts.
Over time, it will completely disappear.
A few comets come close enough to Earth for us to see them with our eyes.
Halley’s Comet, for example, can be seen from Earth every 76 years.
Words to know
- Comet
- A body made of dirty ice, dust, and gas that orbits the Sun. Scientists believe comets are made up of material left over from when the Sun and the planets were formed.
- Nucleus
- The solid core of the comet. It is mostly ice and gas, with a small amount of dust and other solids.
- Coma
- A dense cloud spewed off by the evaporating nucleus as the comet nears the Sun. Near the Sun, the coma makes the comet look like a big “fuzzy ball.”
- Tail
- The part that streams out behind a comet near the Sun, blown away from the coma by the solar wind. A dust tail can be up to 10 million km long, and an ion tail can be up to 100 million km long.
- Orbit
- The path a comet follows around the Sun. A comet’s orbit takes it very close to and very far away from the Sun.
- Solar wind
- The wind from the Sun. It blows coma material away from the coma to become the comet’s tail, and it pushes the dust and gas released by melting ice away from the comet.
You can also read the page called “What Is an Asteroid? — For Kids”
You can also read the page called “What Is a Meteor Shower?”
Sources
This page was built only from these sources:
NASA StarChild — “Comets” — Solar System Level 1 — https://starchild.gsfc.nasa.gov/docs/StarChild/solar_system_level1/comets.html
NASA StarChild — “How can we fly through the tail of a comet?” — StarChild Question of the Month #27, November 2000 — https://starchild.gsfc.nasa.gov/docs/StarChild/questions/question27.html
Checked November 2, 2026.