In recent years the discovery of extremophiles, bacteria that live in nuclear reactors, hot ocean vents and other unlikely places, and of exoplanets has spurred new work and ideas about habitable planets. If Mars can have microfossils, why not Venus?
Moreover, Dr. Grinspoon said, new studies of Venus have led to the conclusion that the planet might have lost its oceans rather recently, only 700 million years ago, allowing plenty of time since the formation of the planet for life to have evolved and then escaped to the clouds.
What kind of life would that be? In 2004, Dirk Schulze-Makuch, an astronomer at the Technical University Berlin, in Germany, and his colleagues suggested that microbes floating in the clouds could be coated with a compound called cyclooctasulfur that would act as a sunscreen and convert ultraviolet light into visible wavelengths for photosynthesis.
Earlier this year, Dr. Seager and her colleagues