I don’t remember where I got these from. Probably Wikipedia or something.
Asteroid: Asteroidal
Comet: Cometary
Cosmos: Cosmic
Dimension: Dimensional
Ecliptic: Ecliptical, zodiacal
Galaxy: Galactic
Meteor: Meteoric
Meteoroid: Meteoroidal
Multiverse: Multiversal
Nebula: Nebular
Planet: Planetary
Planetoid: Planetoidal
Quasar: Quasaric
Sky: Celestial
Star: Astral, sidereal, stellar
Supernova: Supernovan
Universe: Universal
Sun: Solar, Solarian
Luna: Lunar, Cynthian, Selenian, Selenite
Mercury: Mercurian, Mercurial, Hermean
Venus: Venerian, Venusian, Cytherean
Earth: Earthly, Earthling, Earther, Terran, Terrestrial, Tellurian, Gaian, Gaean
Mars: Martian, Arean
Jupiter: Jovian, Jovial, Jupiterian, Zeusian
Saturn: Saturnian, Saturnine, Cronian, Kronian
Uranus: Uranian, Caelian
Neptune: Neptunian, Poseidean
Ceres: Cererian
Eris: Eridian
Orcus: Orcean, Orcan
Pallas: Palladian
Pluto: Plutonian, Plutonic
Sedna: Sednian
Vesta: Vestian, Vestan
Adjectives for moons are only listed if they differ from what an average English-speaking monoglot might expect, because… there’s a lot of them.
Phobos: Phobian
Deimos: Deimian
(I would argue in favor of “Phobic” and “Deimic”, myself, but the last time I tried they kicked me out of NASA HQ.)
Io: Ionian
Leda: Ledian, Ledean
Metis: Metidian
Bergelmir: Bergelmian
Fenrir: Fenrian
Surtur: Surtian
Suttungr: Suttung, Suttungian
Thrymyr: Thrymian
Ijiraq: Ijiraupian, Ijirauqian
Kiviuq: Kiviupian, Kiviuqian
Paaliaq: Paaliapian, Paaliaqian
Siarnaq: Siarnaupian, Siarnaqian
Tarqeq: Tarqiupian, Tarqeqian
Nix: Nictian
Styx: Stygian