Nearly 40 years ago, scientists first predicted the existence of helium rain on planets, primarily composed of hydrogen and helium, such as Jupiter and SaturnHowever, it has not been possible to achieve the experimental conditions necessary to validate this hypothesis – until now.
In a paper published on May 26, 2021 by natureScientists reveal experimental evidence to support this long-standing forecast, showing that helium rain is possible during pressures and temperature conditions that reflect what is expected to occur within these planets.
“We discovered that helium rain is real and can occur in both Jupiter and Saturn,” said Marius Millot, a physicist at Lawrence Livermore National Laboratory (LLNL) and co-author of the publication. Allowing planetary scientists to decipher how these planets formed and evolved, which is critical to understanding how the solar system formed. “
“Jupiter is particularly interesting because it is thought to help protect the inner planetary regions that Earth formed,” added Raymond Jeanloz, co-author and professor of Earth and Planetary Sciences and Astronomy. University of California Berkeley. “We might be here because of Jupiter.”
An international research team, which includes scientists from LLNL, the French Alternative Energy Commission and the Atomic Energy Committee, the University of Rochester and the University of California, Berkeley, conducted their experiments at the University of Roches’ Laser Energetics Laboratory. Router (LLE)
“Steady compression and laser-powered shocks are key to helping us reach conditions comparable to that of Jupiter and Saturn’s interior. But it’s very challenging, ”said Millot.“ We really have to use this technique to get reliable evidence. The team took many years and got a lot of creativity. “
The team used diamond anvil cells to compress a mixture of hydrogen and helium into 4 gigapascals (GPa; About 40,000 times the Earth’s atmosphere) .Then, the scientists used the giant 12-beam beam of LLE omega lasers to emit intense shockwaves to compress samples to a final pressure of 60-180 GPa and provide Hot up to thousands of degrees Similar methods are key to discovering superionic water ice.
The team used a series of ultra-fast diagnostic tools to measure the shock velocity, reflectivity of samples compressed by shock and heat radiation, finding that the sample’s reflectance did not increase smoothly when present. The impact pressure is increased, as in most examples. The researchers studied with similar measurements. But they found discontinuities in the observed reflections, indicating a sudden change in the conductivity of the samples, signatures of a separate mixture of helium and hydrogen. In a paper published in 2011, LLNL scientists Sebastien Hamel, Miguel Morales and Eric Schwegler recommend the use of reflection dynamics as a probe for demixing processes.
“Our experiments revealed experimental evidence for a long prediction: there are many pressures and temperatures where this mixture is unstable and mixed,” Millot said. And what is needed to convert hydrogen into a metal liquid, and the easy-to-understand picture is to make hydrogen a catalyst for demixing. “
Simulating this numerical demixing process is challenging because of its subtle quantum effects. These experiments are important benchmarks for numerical theory and simulation. Looking ahead, the team will continue to refine the measurements and expand to other elements in an effort to improve our understanding of the material in extreme conditions.
Reference Material: “Evidence of the immobility of isc helium hydrogen at Jupiter’s intrinsic conditions” by S. Brygoo, P. Loubeyre, M. Millot, JR Rygg, PM Celliers, JH Eggert, R. Jeanloz and GW Collins, 26 May 2021, nature.
DOI: 10.1038 / s41586-021-03516-0
The work was funded by the LLNL Direct Laboratory Research and Development Program and the Department of Energy’s Office of Science. In addition to Millot and Jeanloz, collaborators include Stephanie Brygoo and Paul Loubeyre of CEA Peter Celliers and Jon Eggert of LLNL; And Ryan Rygg and Gilbert Collins from the University of Rochester.