Planetary science (rarely planetology) is the scientific study of planets (including Earth), moons, and planetary systems, in particular those of the Solar System and the processes that form them. It studies objects ranging in size from micrometeoroids to gas giants, aiming to determine their composition, dynamics, formation, interrelations and history. It is a strongly interdisciplinary field, originally growing from astronomy and earth science, but which now incorporates many disciplines, including planetary astronomy, planetary geology (together with geochemistry and geophysics), atmospheric science, oceanography, hydrology, theoretical planetary science, glaciology, and the study of extrasolar planets. Allied disciplines include space physics, when concerned with the effects of the Sun on the bodies of the Solar System, and astrobiology.

Die Planetologie ist die Wissenschaft, die sich mit den einzelnen nichtstellaren Himmelskörpern und den Planetensystemen im Allgemeinen befasst. Dazu gehört die Untersuchung

La planétologie est la science de l'étude des planètes. La discipline recouvre de nombreuses branches de la science ; son domaine d'étude s'étend des grains microscopiques jusqu'aux planètes géantes gazeuses.

Planetologia (nauki planetarne) - dział astrofizyki zajmujący się badaniem budowy i ewolucji systemów planetarnych, planet, księżyców, planetoid, komet oraz mniejszych ciał niebieskich, a także procesów na nich zachodzących.

Per planetologia (chiamata anche scienza planetaria o astronomia planetaria) si intende lo studio delle proprietà fisiche dei corpi planetari, spesso non limitato ai soli pianeti ma esteso a tutti i corpi celesti non stellari, interni ed esterni al sistema solare; in genere si annoverano tra gli studi di planetologia anche quelli riguardanti le origini dei sistemi planetari e la loro evoluzione dinamica.