Hothouse Planet

A Hothouse Planet is a terrestrial planet that has an overly thick atmosphere full of greenhouse gasses, like Venus. They are likely to be barren worlds, choked with a heavy and noxious atmosphere, perhaps with all their oceans having boiled away in a process known as the runaway greenhouse effect.

The runaway greenhouse effect is caused by strong tidal forces from the planet's star. The area around a star in which the runaway greenhouse effect could take place but in which the atmosphere of the planet is not evaporated is called the Venus Zone. A hothouse planet could also be the result of runaway climate change on a previously habitable world, perhaps having been caused by an industrial civilisation.

Worldbuilding in Practice
"Ingersoll is a hothouse planet orbiting the K star Boltzmann. At first sight it appears to be a typical Venusian hothouse. However, it orbits within the habitable zone: too far from the star for it to have formed such a hostile atmosphere naturally. Upon further investigation, scientists made the discovery of ruined cities on the planet's surface, belonging to a pre-spacefaring industrial society that had likely choked their atmosphere with greenhouse gases from industrial centres, eventually sparking a runaway greenhouse effect. Evidence indicates that before the planet's oceans evaporated (several million years ago), it was a thriving garden world with a thriving biosphere." "Despite the ancient tragedy, not all life on Ingersoll was eradicated. Some microbial life lives in clouds the upper atmosphere, where they are spared the worst effects of the planet's hostile weather."