TRAPPIST-1 c enters the Codex as the second of seven rocky worlds circling an ultracool M8 red dwarf about 41 light-years away in Aquarius. Roughly 1.1 × Earth in radius and about 1.3 Earth masses, it completes an orbit every 2.4 days and receives about twice the starlight Earth does, placing it just inside the inner edge of the habitable zone. In 2023, JWST’s MIRI instrument measured its dayside glow at 15 microns and found a temperature near 380 K, ruling out a thick carbon-dioxide atmosphere like Venus’s. What remains is most likely bare rock or, at most, a thin veil poor in carbon dioxide. It stands in the Galactic Codex as the would-be Venus twin that appears to have lost its sky.
