TOI-270 d enters the Codex as the outermost of three worlds circling a quiet M-type red dwarf some 73 light-years away in the southern constellation Pictor. Roughly 2.0 × Earth in radius and about four to five Earth masses, it completes its orbit every 11.4 days, warmed to an equilibrium near 350–380 K, inside the inner edge of its star’s habitable zone. JWST spectra revealed methane, carbon dioxide, and water vapor threaded through a strikingly metal-rich envelope, with roughly half its atmospheric mass in heavy volatiles. Some astronomers read a rocky interior beneath a supercritical, well-mixed atmosphere; others argued for a deep water layer under hydrogen skies. Either way, it stands as a template for the galaxy’s most common kind of world.
