A comet is a chunk of ice that travels in an elongated orbit around the sun. When the comet gets close to the sun – in the inner solar system – it heats up and the ice starts to evaporate. In this way, dust and gas trapped inside the ice are released.
The sunlight will also cause a tail to form instead of the dust grains orbiting the comet.
The radiation from the sun puts pressure on the dust, so the tail always turns away from the sun. The sunlight is also reflected by the dust so that the comet can be distinguished from Earth.
Two tails
In fact, a comet can have two tails – one made of dust and the other made of gas molecules.
When the sun’s rays hit gas molecules, they can strip electrons from the molecules, which gain an electrical charge. This electric gas of electrons and positively charged molecules interacts with the stream of charged particles from the sun, the so-called solar wind.
In this way, the electric gas forms its own tail that points away from the sun. Next to the comet, where the amount of charged particles is the highest, the tail can shine with blue light.
A comet’s nucleus is usually a few kilometers in diameter, but its tail can stretch hundreds of millions of kilometers into space.
Tailless comets are found where all material that can evaporate has disappeared, leaving only the nucleus and nothing that can form a tail.
