Helium falls like rain on Jupiter

Posted by Emma Woollacott

New research suggests that it's raining helium in the interior of Jupiter. UC Berkeley scientists reckon this is the best way to explain why there's so much less neon in the outer layers of the planet than predicted.

"Helium condenses initially as a mist in the upper layer, like a cloud, and as the droplets get larger, they fall toward the deeper interior," said Hugh Wilson, co-author of a report appearing this week in Physical Review Letters.

"Neon dissolves in the helium and falls with it. So our study links the observed missing neon in the atmosphere to another proposed process, helium rain."

The UC Berkeley team used density functional theory to predict the properties of Jupiter's interior.

They embarked on their current research because of a discovery by the Galileo probe that all elements seemed to be slightly enriched compared to the abundance on the sun, except for helium and neon. Neon stood out because it was one-tenth as abundant as it is in the sun.

Their simulations showed that the only way neon could be removed from the upper atmosphere is to have it fall out with helium, since neon and helium mix easily.

Their calculations suggest that at about 10,000 to 13,000km into the planet, where the temperature about 5,000 degrees Celsius and the pressure is over a million times that on Earth, hydrogen turns into a conductive metal. Helium, not yet a metal, does not mix with metallic hydrogen, so it forms drops, like drops of oil in water.

"As the helium and neon fall deeper into the planet, the remaining hydrogen-rich envelope is slowly depleted of both neon and helium," co-author Burkhard Militzer said. "The measured concentrations of both elements agree quantitatively with our calculations."