GJ 436 b stands as a warm ice giant orbiting a nearby red dwarf M-type star 32 light-years from Earth. With a radius of 4.2 × Earth and a mass of 22.1 Earth masses, it completes an orbit every 2.64 days at 0.029 AU, far inside the habitable zone. Intense stellar heat drives a vast hydrogen envelope streaming away like a comet’s tail, revealing how Neptune-class worlds erode when they orbit close to cool stars. This nearby transiting analog offers a clear window into ice-giant atmospheres and escape. It endures in the Galactic Codex as the archetype that opens the ledger of worlds between rocky planets and gas giants.
