The search for signs of life on other planets has an unlikely new target. The atmospheres of brown dwarfs – gaseous objects too big to be a planet and too small to be a star – might have the capacity to support life.

Brown dwarfs aren’t massive enough to sustain nuclear fusion, the process that powers stars. But they do produce heat early in their lives. Once their fuel is exhausted they begin to cool.

“One reason we’re interested …