Particle physics experiments

Laser experiments suggest helium rain is falling on Jupiter


Helium rains may fall on Jupiter.

At the pressures and temperatures present in the gas giant, the hydrogen and helium that make up most of its atmosphere do not mix, according to laboratory experiments reported on May 27. Nature. This suggests that deep in Jupiter’s atmosphere, hydrogen and helium separate, with helium forming droplets that are denser than hydrogen, causing them to rain (ND: 04/19/21).

Jupiter’s marbled exterior is fairly familiar territory, but it’s still unclear what’s going on well below cloud tops. So the researchers designed an experiment to compress hydrogen and helium, reaching pressures nearly 2 million times Earth’s atmospheric pressure and temperatures of thousands of degrees Celsius, similar to the inner layers of gas giants.

“We are reproducing the conditions inside the planets,” says physicist Marius Millot of Lawrence Livermore National Laboratory in California.

Millot and his colleagues squeezed a mixture of hydrogen and helium between two diamonds and hit the mixture with a powerful laser to compress it even more. As the pressure and temperature increased, the researchers saw a sharp increase in the degree of reflection of the material. This suggests that the helium separated from the hydrogen, which becomes a liquid metal under these conditions (NS: 08/10/16). At even higher pressures and temperatures, the reflectivity decreased, suggesting that the hydrogen and helium began to mix again.

The researchers calculated that the hydrogen and helium would separate about 11,000 kilometers below Jupiter’s cloud tops, to a depth of about 22,000 kilometers.

The results could help scientists explain the observations made by the Galileo spacecraft (NS: 02/18/02) and Juno (ND: 03/07/18), such as the fact that the outer layers of Jupiter’s atmosphere contain less helium than expected.