Comets

Comets are like dirty snowballs orbiting around the Sun. The solid body of the comet is called the nucleus, consisting of rock, ices, and dust. Dust is a common word used in astrochemistry in reference to molecules in their solid form. As a comet approaches the inner Solar System, the Sun’s radiation heats up the comet nucleus and molecules evaporate into the gas-phase forming what we know as the coma, a spherical atmosphere around the nucleus. Other features characteristic to a comet are the dust and ion tails. The ion tail is the result of solar radiation interaction with ions in the coma, forming a trail of ions that always point away from the sun. Another result of the Sun’s radiation pressure and solar winds is the formation of a dust trail, which follows a curved tail path away from the sun. With the use of telescopes and other scientific instruments to study the composition of comets' surfaces and tails, scientists have discovered that comets harbor ingredients essential to life such as amino acids and sugars as well as simpler molecules. Comets are speculated to have brought these very ingredients to surfaces such as Earth.

Comets were likely to have formed in the early stages of the Solar System’s formation, leading to the big question of when did comets form and how does their chemical composition evolve over time? To resolve these questions, scientists use radio telescopes such as the Atacama Large Submillimeter/Millimeter Array (ALMA) to study the gas species in a comet’s tail and most recently, the James Webb Space Telescope (JWST) to observe in the infrared, which makes it possible to study surface species on the nucleus of the comet. Additionally, probes (such as in the Rosetta mission) have been sent into orbit alongside comets to get real-time detections of material present in the tail and land on the surface of the comet. Theoretical astrochemists also contribute to this research area by using astrochemical models to predict the abundance of molecules and the chemical reactions responsible for what we see in comets.