Science The results show the range of blistering temperatures and crushing pressures at which this takes place. by Eric Hand
'But they also suggest that a helium rain could also fall on Jupiter, where such behavior was almost completely unexpected.
'“We’re showing the first experimental evidence at conditions relevant to Jupiter and Saturn,” says Gilbert Collins, an extreme matter physicist at Lawrence Livermore National Laboratory (LLNL) in Livermore, California. “It’s a surprise that [this] happens over such a broad regime of temperatures and densities.” Collins described the results in a talk yesterday at a meeting of the American Geophysical Union in San Francisco, California.
'Saturn is more than 50% brighter than it ought to be for a normally cooling planet. One way to account for this is through the behavior of its massive envelope of hydrogen and helium gases. As temperatures and pressures rise in the planet’s interior, the gases become liquids. At still deeper levels, the liquid hydrogen becomes electrically conductive, or metallic, while the liquid helium remains mixed in. But once conditions surpass a certain threshold of pressures and temperatures, the liquid helium is expected to fall out of the dissolved mixture. According to theory, this liquid helium forms droplets of “rain” that fall farther towards Saturn’s core, unleashing gravitational potential energy that makes Saturn more luminous.
'Theorists imagined this could never happen on Jupiter, which is hotter than Saturn. This extra heat is thought to stir up the helium-hydrogen mixtures more vigorously, preventing the helium from falling out as rain. Theories have suggested helium rain on Saturn since the mid-1970s, but experimental evidence has been lacking.'