What’s trailing behind and in front of these rocks as they hurtle through space?
Comets are small, icy bodies in orbit around the Sun surrounded by a gaseous coma that consists of water, carbon dioxide and other gases. The most noticeable features of a comet are its tails, with most having two, a dust and ion tail. Both tails point away from the Sun at varying angles due to the solar wind, regardless of the comet’s directions.
The dust tail of a comet appears whitish-yellow, because its microscopic dust particles reflect sunlight. It is anywhere from 1 to 10 million km (600,000 to 6 million miles) in length, pushed out from the comet by the solar wind and curving slightly because of the comet’s orbit around the Sun. The other tail, known as the plasma or ion tail, is composed of charged gases (ions) such as carbon monoxide, and stretches as far as 160 million km (100 million miles) from the comet.
This means that when the comet approaches the Sun the tail runs behind it, but when the comet moves away from the Sun, the ion tail leads in front of the comet.
Three’s a crowd
Hale-Bopp is the only comet observed to have a third tail, made of sodium. This faint tail extends 50 million km (31 million miles) behind the comet in between the dust and ion tail, yet the cause of it is unknown.