Flying aliens. Computer artwork of possible alien life forms in the clouds of a gas giant planet. It is thought that under such conditions, like those found on Jupiter, life may evolve to float at the optimum level in the atmosphere using gas-filled balloon-like buoyancy structures. They would float on the wind and could use their tentacles to feed on smaller floaters and organic debris. Jupiter's atmosphere is mostly hydrogen, with pressure and temperature rising swiftly with depth. The clouds consist of chemicals like methane, ammonia, water and hydrogen sulphide, all formed by the action of sunlight and Jupiter's internal heat.