Cereans live on Ceres (in the future)

There are many terms from classic and modern SF that remain unresearched, and the Historical Dictionary of Science Fiction will be continually updated, especially as additional resources are put online. Boing Boing is syndicating new entries from the HDSF on a regular basis. (Read the series introduction.)

Cerean (noun and adjective)

There are many science-fictional demonyms, or names for people from particular places; we explored one of them last month. Typically these refer to planets, moons, or star systems. Asteroids are a different category, because most of them are too small to inhabit, or to bother giving a name to their inhabitants. Instead, we have names for denizens of asteroids in general: asterite, for example, or Larry Niven's term Belter for someone who lives in an asteroid belt.

One exception is Ceres, an object whose classification is itself a matter of some contention. It was originally considered an asteroid, but is now regarded as a dwarf planet; whether it is an asteroid as well is up for debate. Regardless, it is found in our solar system's asteroid belt, and it is the first asteroid-like object discovered, in 1801, and people were conjecturing inhabitants by the name of Cereans before the end of the 19th century.

While Ceres is the largest such object around, Vesta, Pallas, and Hygiea are also sizeable; the first of these has also generated the demonym Vestan (and its related adjective), in use by SF writers from the 1940s onwards.

We should also note that there's also a species known as Cereans in the Star Wars universe; these are from the (fictional) planet Cerea. The HDSF does not generally enter names of this sort unless they are known more widely than their source, as is the case with, for example, Wookiees or Vulcans.