Kepler-452b looks less like a cousin and more like a cautionary warning. The planet orbits a star slightly brighter than the Sun, and over long spans that extra stellar flux changes everything, because even a modest increase in incident radiation can trigger runaway greenhouse feedbacks that lock in heat instead of letting a planet cool through infrared emission.
The hard claim from recent modeling is blunt: by now, Kepler-452b is probably dry. Once water vapor thickened its atmosphere, absorption of outgoing longwave radiation amplified surface heating, oceans started to evaporate, and photodissociation in the upper atmosphere let hydrogen escape to space, a classic atmospheric escape pathway that permanently reduces a world’s water inventory and prevents any simple return to temperate conditions.
The romantic label “Earth’s cousin” ignores a basic stellar arithmetic. A slightly higher luminosity, applied for a longer main-sequence lifetime, means integrated energy delivery that pushes the planet’s orbit effectively inward relative to the shifting habitable zone, so climate models now place Kepler-452b beyond the inner edge, in a regime more comparable to a slow-motion Venus than to a blue, ocean-bearing Earth.
