A comet is an icy body that is small and can develop a ‘tail’ of gas as it approaches the Sun from the outer Solar System. If you spotted comet C/2023 A3 (Tsuchinshan-ATLAS) in person or saw photos online this October, you might have been inspired to learn more about these visitors from the outer Solar System. The key traits of a comet are its nucleus, coma, and tail.
Comet McNaught over the Pacific Ocean. Image taken from Paranal Observatory in January 2007. Credits: ESO/Sebastian
The nucleus of the comet is comprised of ice, gas, dust, and rock. This central structure can be up to 80 miles wide in some instances– large for a comet but too small to see with a telescope. As the comet reaches the inner Solar System, the ice from the nucleus starts to vaporize, converting into gas. A glowing gas cloud that forms around the comet as it approaches the Sun is called the coma.
The most prominent feature is the tail of the comet. The brightest comets show a white-colored dust tail. When photographing comets, you can sometimes resolve the second blue-colored tail, made of ionized gases that have been electronically charged by solar radiation. Both tails always point away from the Sun. In 2007, NASA’s STEREO mission captured images of C/2006 P1 McNaught and its dust tail, stretching over 100 million miles. Solar wind influenced both tails, creating striations and giving the tails a feathered appearance in the sky.
Coming and Going
Comets appear from beyond Uranus, in the Kuiper Belt, and may even come from as far as the Oort Cloud. These visitors can be short-period comets like Halley’s Comet, returning every 76 years. This may seem long to us, but long-period comets like Comet Hale-Bopp, observed from 1996-1997 won’t return to the inner Solar System until the year 4385. Other non-periodic comets, like NEOWISE, only pass through our Solar System once.
But our experiences of these comets are not limited to the occasional fluffy snowball. As comets orbit the Sun, they can leave a trail of rocky debris. When Earth passes through one of these debris fields, we experience meteor showers! The most well-known is the Perseid meteor shower, caused by Comet 109P/Swift-Tuttle. While this meteor shower happens every August in the northern hemisphere, we won’t see Comet Swift-Tuttle again until the year 2126.
Comet McNaught over the Pacific Ocean. Image taken from Paranal Observatory in January 2007. Credits: ESO/Sebastian Deiries
