Aeronomy concerns the study of the atmosphere i.e., all atmospheres, terrestrial as well as… “extraterrestrial”, like the atmospheres around comets or other planets from the solar system in which similar phenomena we already know on Earth, may occur.
Extra terrestrial atmospheres can provide us with precious information about our own atmosphere, its history, its future and even about the origins of life on Earth!
The study of Earth-like planets, whose atmospheres have evolved towards different and extreme conditions, is a vital part of the understanding of the past and future of our subtle climate system.
Within our solar system only two planets other than the Earth have atmospheres over a rocky core:
Titan (one of the moons of Saturn) also has an atmosphere.