Atmospheric Beast

Atmospheric beasts are wingless, lighter-than-air lifeforms rumored to inhabit the atmosphere of Earth and possibly other planets. Sighted by people all around the world, they have gathered interest from ufologists, cryptozoologists, supernatural researchers and astrobiologists.

Cryptozoology author Ivan T. Sanderson has devoted an entire book to the theory that many UFOs are not alien aircrafts, but rather low density organisms native to the skies; and the idea has been supported by the discovery of perpetually airborne microorganisms, which spend their whole lives floating high in the air; as well as microscopic algae that live permanently in the clouds.

Additionally, astronomers such as Carl Sagan have also proposed that creatures like these could potentially inhabit the atmosphere of Jupiter and other gas giants.

Biology
Atmospheric beasts are often described as large, balloon-like organisms, whose bodies are filled with hydrogen or other gases. On planets like Jupiter, where the atmosphere is mainly composed of hydrogen, the beasts would need to have hot hydrogen inside their bodies, since there is no other lighter substance.

Not all atmospheric beasts are built like living balloons. Some are described as having tentacles or flipper-like organs. In some reports, they are actually cloud-like, being not completely solid, and able to change their density and their size.

Another mysterious phenomenon called "star jelly" is often linked to atmospheric beasts. A famous idea is that when an atmospheric beast dies, it falls from the sky as star jelly, a smelly gelatinous mass that usually evaporates in less than a few hours.

Some believe that atmospheric beasts are Earth organisms, genetically related to the other lifeforms in our world. Others prefer to think that they are some sort of extraterrestrial being, sometimes thought to be space-borne creatures. Having originated on Earth or in space, atmospheric beasts are nevertheless largely thought to be non-sapient, and thus are viewed more as animals than as aliens that we might be able to communicate with.