The adjectival forms of the names of astronomical bodies are not always easily predictable.
Attested adjectival forms of the larger bodies are listed below, along with the two small Martian moons; in some cases they are accompanied by their demonymic equivalents, which denote hypothetical inhabitants of these bodies.
For instance, for a large portion of names ending in -s, the oblique stem and therefore the English adjective changes the -s to a -d, -t, or -r, as in Mars–Martian, Pallas–Palladian and Ceres–Cererian;[note 1] occasionally an -n has been lost historically from the nominative form, and reappears in the oblique and therefore in the English adjective, as in Pluto–Plutonian and Atlas–Atlantean.
In practice forms ending in -ean may be pronounced as if they were spelled -ian even if the e is long in Latin.
This dichotomy should be familiar from the dual pronunciations of Caribbean as /ˌkærɪˈbiːən/ KARR-ə-BEE-ən and /kəˈrɪbiən/ kə-RIB-i-ən.