Comets

By: Marigold So

What are Comets?Comets are celestial bodies of

small mass that travel around the Sun, usually in elongated orbits. They become visible as they near the Sun and sometimes they form a visible tail.

This is an icy body that releases gas or dust. They are often compared to dirty snowballs, though recent research has led some scientists to call them snowy dirtballs.

Comets contain dust, ice, carbon dioxide, ammonia, methane and more. Astronomers think comets are leftovers from the gas, dust, ice and rocks that initially formed the solar system about 4.6 billion years ago.

Parts of a CometAristotle compared the physical

appearance of what he believed to be rare emissions from Earth to hair flowing from a human head. He called them kometes, which literally meant “long haired”. Although Aristotle didn’t understand the true nature of comets, his name obviously stuck. So what was Aristotle really seeing in the night sky?

Aristotle

1. The NucleusThe Nucleus essentially

comprises the entire comet when it is far from the sun, during which time it is frozen.

The nuclei can remain in a solid, pristine state, unobserved by even the world’s most powerful telescopes until it approaches the Sun.

The ComaThe cold, solid nucleus warms

as it approaches the Sun and the comet begins to transform. Expelled water, dust, gas and debris form a fuzzy haze around the nucleus called the coma.

This happens when the comet is about 7.5 x km from the sun.

A comet’s coma can span a few miles in diameter to hundreds of thousands. 

The Dust TailAs the nucleus and coma move

closer to our Sun, the comet continues its transformation into one of the most breath-taking objects on our solar system. Heavier particles and debris are released by vaporizing ices. They form another part of the comet called the dust tail.

There can even be more than one dust tail.

The Ion TailSome ionized gases are

pushed directly away from the Sun by the Sun’s high speed solar wind. These ionized gases form the comet’s blue, ion tail.

Both the ion and dust tail(s) can be hundreds of thousands or even millions of miles long.

Parts of a Comet

Origin of CometsIn 1950 the Dutch Astronomer Jan

Oort proposed that the Sun is surrounded by an enormous “cloud” of comet material at a distance about 1,000 times that of the radius of the known solar system.

This theory was followed in 1951 by Dutch-American astronomer Gerard Kupier’s proposal that a ring of cometary material lies in the plane of the solar system, several hundred times as far from the Sun as the Earth is.

Gerard Kuiper1905-1973

Kuiper BeltThis is sometimes called the Edgeworth–

Kuiper belt, is a circumstellar disc in the Solar System beyond the planets, extending from the orbit of Neptune (at 30 AU) to approximately 50 AU from the Sun.

This is an area around the sun that extends about 30-100 astronomical unit.

The Kuiper Belt

Oort CloudThe Oort Cloud is an extended shell of icy

objects that exist in the outermost reaches of the solar system.

It is named after astronomer Jan Oort, who first theorised its existence.

The Oort Cloud is roughly spherical, and is thought to be the origin of most of the long-period comets that have been observed.

The Oort Cloud is very distant from the Sun and it can be disrupted by the nearby passage of a star, nebula, or by actions in the disk of the Milky Way. Those actions knock cometary nuclei out of their orbits, and send them on a headlong rush toward the Sun.

The Oort Cloud

Orbit of Comets Comets go around the Sun in a highly

elliptical orbit. They can spend hundreds and thousands of years out in the depths of the solar system before they return to Sun at their perihelion.

Like all orbiting bodies, comets follow Kepler's Laws - the closer they are to the Sun, the faster they move.

While a comet is at a great distance from the Sun, its exists as a dirty snowball several kilmoeters across. But as it comes closer to the Sun, the warming of its surface causes its materials to melt and vapourise producing the comet's characteristic tail. Comet tails can be as long as the distance between the Earth and the Sun.

Orbit of a Comet

Top 10 Famous Comets

http://listosaur.com/science-a-technology/10-famous-comets-in-history/

10. Comet Lovejoy

9. Comet McNaught

7. Lexell’s Comet

8. Comet Hale-Bopp

6. The Eclipse Comet of 1948

5. The Great January Comet of 1910

4. The Great March Comet of 1843

3. The Great

2. The Great Comet of 1680

1. Halley’s Comet

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