Researchers simulate gas giant inner life

X-ray laser experiment provides important data for planetary models

The Jupiter gas planet recorded by the Cassini-Huygens space probe © NASA / JPL / Space Science Institute
Read out

Whirling storms, huge pressure and an impenetrable soup of condensing gas: this is how the lower atmospheric layers of the big gas planets like Jupiter and Saturn look like. German scientists have now experimentally reconstructed the suspected conditions inside these planets. With an X-ray laser they recorded this in super slow motion. With their published in the journal "Physical Review Letters" results, they hope to improve existing models of gas planets.

The atmosphere of gas planets such as Jupiter is largely hydrogen, the most common chemical element in the universe. However, what exactly it looks like inside the gas giant is still unknown, only models exist. Scientists assume that the hydrogen in the depths of Jupiter is initially fluid due to the tremendous pressure. Even farther inside the largest planet of our solar system could even be metallic solid hydrogen. Such conditions are difficult to reproduce on Earth, so direct comparison measurements are missing.

Scientists led by Ulf Zastrau from the University of Jena have at least partially recreated the interior of the large gas planets in an elaborate experiment at the Deutsches Elektronen-Synchrotron (DESY) in Hamburg.

Hydrogen condenses in the copper block

"Little is known experimentally about the hydrogen inside such planets, " explains Zastrau. "Even if the theoretical models are already very good. Liquid hydrogen has a density that corresponds to the lower atmospheric layers of large gas planets. "So first, the researchers needed liquid hydrogen to simulate the conditions of a gas giant.

For this purpose, they pressed high-purity hydrogen from a commercially available gas cylinder through a copper block, which is cooled with liquid helium. In the copper block, the hydrogen is frozen, condensing to the liquid. "The temperature has to be controlled very precisely. If the hydrogen becomes too cold, it freezes and clogs the pipe, "says DESY researcher Sven Toleikis. At the end of the copper block, a nozzle protrudes like a finger into the vacuum chamber. From its tip flows a fine jet of liquid hydrogen, which has a diameter of only one fiftieth of a millimeter. display

In one trillionth of a second to 12, 000 degrees

"What we do is laboratory astrophysics, " explains Zastrau. The physicists bombarded the hydrogen beam with X-ray pulses from DESY's free-electron laser FLASH. These X-ray laser flashes first heat the electrons of the hydrogen, which gradually release this energy to the approximately 2, 000 times heavier protons. The bonds of the normally two-atom hydrogen molecules break and a plasma of electrons and protons is formed. Because the FLASH pulses are so high-energy, the liquid hydrogen heats up at a single stroke from minus 253 degrees Celsius to about 12, 000 degrees Celsius.

Experimental setup on DESY's X-ray laser FLASH. Ulf Zastrau / University of Jena

"For the investigation, we used the unique ability of FLASH to divide up the individual flashes, " explains Toleikis. The first half of the flash heats up the hydrogen, with the second half can then examine its properties. Examined the system in this way at slightly different times, can be observe in a kind of super slow motion how a thermal equilibrium between the electrons and the protons in the hydrogen is established. The experiments showed that this happens within a trillionth of a second.

Refining Calculation Models: The first step is done

Important parameters for the computational models of the inner atmosphere of the gas planets are the so-called dielectric properties of hydrogen. These include, among other things, the heat and the electrical conductivity, because in the large gas planets there is a strong heat transfer from inside to outside.

"The investigation detracts from the dielectric properties of liquid hydrogen, " reports Philipp Sperling of the University of Rostock, co-author of the publication. If one knows what thermal and electrical conductivity the individual hydrogen layers have in the atmosphere of a gas planet, the associated temperature profile can be calculated from this Vielt much about the processes inside the gas planets and will refine the existing models.

To create a detailed picture of the entire planetary atmosphere, however, scientists must repeat their experiments at other pressures and temperatures. However, the important first step has been taken: "Our experiment has shown us the possibilities of investigating dense plasmas with X-ray lasers, " emphasizes co-author Thomas Tschentscher, scientific director of the R ntgenlaser European XFEL. "This method opens the way for further investigations, for example, on denser plasmas of heavier elements and mixtures, as they occur in the interior of planets." Even the partially mysterious properties of planets outside of our Solar system, the researchers hope to be able to enlighten soon.

(Physical Review Letters, 2014)

(German Electron Synchrotron DESY, 12.03.2014 - AKR)