Why helium may fall through Jupiter
Deep inside Jupiter, pressure becomes so immense that hydrogen and helium may no longer remain evenly mixed. The hydrogen-rich surroundings can push helium out of solution, much as oil separates from water—though the conditions inside a giant planet are far more extreme. The separated helium can gather into droplets and sink through the atmosphere. This proposed process is called helium rain.
A slow fall that releases heat
As helium droplets descend, gravity pulls them into warmer, denser layers. Their gravitational energy is converted into heat, which can help explain how Jupiter continues to give off more energy than it receives from sunlight. The rain would not be a storm of large, solid chunks: it is a gradual separation and settling of helium within the planet.
Scientists infer this process from models of how hydrogen and helium behave at high pressure, rather than from direct observation of Jupiter’s deep interior. If helium is raining out, it would also leave the planet’s outer layers relatively depleted in helium compared with its original mixture. Far below the cloud tops, the falling droplets would eventually rejoin the deeper interior—helping Jupiter redistribute both heat and helium.
