From the Sea – What is a Comet? Comets are large objects made of dust and ice that orbit the Sun.
These ancient objects are remnants of the formation of the solar system 4.6 billion years ago. Comet famous because of its long, flowing tail.
Comets are mostly found in the solar system. Some exist in a wide disk beyond Neptune’s orbit called the Kuiper Belt. Scientists call this a short period comet.
This comet takes less than 200 years to orbit the Sun.
Another comet is in the Oort Cloud, at the outer edge of the spherical solar system. These are called long-period comets because they take longer to orbit the Sun.
According to Spaceplace.nasa.govthe comet with the longest known orbit takes more than 250,000 years to make one single trip around the Sun.
What brings comets so close to Earth that we can see them? The gravity of a planet or star can pull a comet from its home in the Kuiper Belt or Awan Oort.
This pull can direct the comet toward the Sun. The path of this directed comet looks like a long stretched oval.
As a comet is pulled faster and faster toward the Sun, swings behind the Sun, then returns to where it came from.
Some comets point towards the Sun and are never seen again. When comets are in the inner solar system, either coming or going, that’s when we can see them in our sky.
What are the parts of a comet? The core of every solid, frozen comet is called the nucleus. These balls of dust and ice are typically less than 16 kilometers across – roughly the size of a small town.
When comets are in the Kuiper Belt or the Oort Cloud, scientists believe they have quite a lot of them – just frozen cores.
But as the comet approaches the Sun, it begins to heat up. Eventually, the ice begins to turn into gas. It can also cause a jet of gas to escape from the comet, taking dust with it.
The gas and dust creates a large, hazy cloud around the nucleus called a coma.
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A comet represented as a blue circle with a yellow center and a white dot in the center has a light blue tail flowing up and to the side and a light yellow tail flowing outward (See Figure).
Why do comets have tails? As dust and gas flow away from the nucleus, sunlight and particles emanating from the Sun push them into tails bright which stretches behind the comet for millions of miles.
When the astronomers took a closer look, they found that the comet actually had two separate tails.
One looked white and made of dust. This tail of dust traces a wide, curved path behind the comet.
The other tail is bluish in color and is made up of electrically charged gas molecules, or ions. The tail of the ion always points directly away from the Sun.
The black curved line is dotted with small blue circles, representing the comet’s movement along its path. Each blue circle has one yellow tail and one blue ribbon that extends.
The blue tail is straight and points directly away from the Sun, while the yellow tail is curved and away from the Sun in a different direction.
Comets have two tails that get longer and closer to the Sun. Both tails are always directed away from the Sun.
The ion tail (blue) always points directly away from the Sun, while the dust tail (yellow) moves away from the Sun in a slightly different direction from the ion tail.
People have been interested in comets for thousands of years. But it’s impossible to get a good view of the comet’s core from Earth because it’s shrouded in coma of gas and dust.
However, in recent years, several spacecraft have had the opportunity to study comets up close.
NASA’s Stardust Mission collects samples from Comet Wild 2 (pronounced like “Vilt two“) and brought it back to Earth.
Scientists found the particles were rich in hydrocarbons, which are the chemicals we think of as the “building blocks” of life.
Thanks to this and other similar missions, we now know more about the structure comet and the types of chemicals found in and around them. Also learn more about the formation of our solar system.
Source: Spaceplace.nasa.gov
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