A planet that cooks metals on one face and freezes the other is not exotic fantasy at all, just harsh orbital bookkeeping. Tidal locking pins one hemisphere toward its star, so the substellar point receives unbroken irradiation that can drive temperatures past metal vaporization thresholds while the nightside never sees direct light.
The odd part is not the heat. The surprise is how little of it spreads. On ultra‑short‑period gas giants such as KELT‑9b and WASP‑76b, extreme gravity and intense stellar flux inflate the atmosphere yet also strip it, leaving a hot, thin, fast day‑to‑night flow that radiates energy away before it can homogenize the globe through advection and convection.
The darker story sits in the physics of radiative cooling and heat capacity. On the dayside, photons escape from high, tenuous layers, so absorbed energy is re‑emitted quickly into space. On the nightside, with no incoming flux and often cloud decks or condensates forming, the limited thermal reservoir loses energy until temperatures plunge toward the floor set only by residual internal heat and inefficient circulation.
The most counterintuitive twist is that metals themselves help enforce the split. At the incandescent limb, refractory elements can exist as atomic vapor, boosting opacity and coupling the gas tightly to the incoming stellar spectrum; downwind, those same elements condense into droplets or grains, drop out of the upper flow, and weaken the radiative link, letting the nightside slide deeper into the cold.
