X-ray scattering enables closer scrutiny of the interior of planets and
stars

Date:
June 24, 2020
Source:
Helmholtz-Zentrum Dresden-Rossendorf
Summary:
An international research team has now presented a new, very precise
method of evaluating the behavior of mixtures of different elements
under high pressure with the help of X-ray scattering. The results
reinforce the premise that the matter in planets like Neptune and
Uranus can alter dramatically: the hot hydrocarbon mixture in the
interior of the ice giants can produce a kind of diamond rain.



FULL STORY ========================================================================== Recreating extreme conditions in the lab, like those in the interior of
planets and stars, is very complex and can only be achieved for fractions
of a second.

An international research team led by the Helmholtz-Zentrum
Dresden-Rossendorf (HZDR) has now presented a new, very precise method
of evaluating the behavior of mixtures of different elements under high pressure with the help of X-ray scattering. The results hone previous measurements and reinforce the premise that the matter in planets like
Neptune and Uranus can alter dramatically: the hot hydrocarbon mixture
in the interior of the ice giants can produce a kind of diamond rain,
as the researchers report in Nature Communications.


========================================================================== Neither solid, nor fluid, neither gaseous, nor a plasma: the matter
inside planets and stars can take on a particular intermediate state,
at a temperature of thousands of degrees, and compressed a thousand
times more than our Earth's atmosphere -- experts call it warm dense
matter. There is a lot we still don't know about it. Lab experiments
are set to change all that but are technically highly complex because
this exotic state does not occur naturally on Earth.

Which all means that both the crafting and study of artificial warm dense matter is a challenge for investigators and theoreticians alike. "But
in the last resort, we have to understand the processes in warm dense
matter if we want to model planets," explains Dr. Dominik Kraus, lead
author of the study and the mastermind behind the measuring method. "We
now have a very promising new approach based on X-ray scattering. Our experiments are delivering important model parameters where, before,
we only had massive uncertainty. This will become ever more relevant
the more exoplanets we discover." Diamond showers -- a planetary energy
source At SLAC National Accelerator Laboratory at Stanford University,
the researchers studied the structure of the matter in mixtures that are typical for planets, in the case of ice giants, hydrocarbon, employing
intense laser light. Standard plastic film served as a substitute for
planetary hydrocarbon. An optical high- energy laser converts the plastic
into warm dense matter: short, strong laser pulses generate shock waves
in the film and compress the plastic to the extreme. "We produce about 1.5 million bars, that is equivalent to the pressure exerted by the weight of
some 250 African elephants on the surface of a thumbnail," says Kraus, illustrating the dimensions. What happens is that the laser shock waves
also heat up the matter to approximately 5,000 degrees. To evaluate
the effect, researchers shoot an extremely powerful X-ray laser at the
sample. Depending on how the light is scattered as it passes through
the sample, they can draw inferences about the structure of the matter.

The researchers observed that in a state of warm dense matter, what
was formerly plastic produces diamonds. The high pressure can split the hydrocarbon into carbon and hydrogen. The carbon atoms that are released compact into diamond structures. In the case of planets like Neptune and
Uranus this means that the formation of diamonds in their interior can
trigger an additional energy source. The diamonds are heavier than the
matter surrounding them and slowly sink to the core of the planet in a
kind of diamond rain. In the process, they rub against their surroundings
and generate heat -- an important factor for planet models.

X-ray scattering enhances measuring precision In an earlier experiment,
Kraus and his team were the first to prove the possible formation
of diamonds in planets using X-ray diffraction in an experimental
setting. But the diffraction patterns of X-ray light can only reveal crystalline structures. Using additional detectors, the researchers
now also analyzed how the light was scattered by the electrons in the
matter. They compared the various scattering components with one another
as well as with theoretical simulations. This process enables precise
scrutiny of the entire structure of matter. "In the case of the ice giants
we now know that the carbon almost exclusively forms diamonds when it
separates and does not take on a fluid transitional form," explains Kraus.

The method is not only more sensitive than X-ray diffraction, it can also
be used more extensively because it makes fewer technical demands on the
light source for the analysis. The international research team is now
planning to apply it to hydrogen mixtures similar to those that occur in gaseous planets and to compressed pure hydrogen as found in the interior
of small stars. These experiments, which are planned to be conducted,
among others, at the Helmholtz International Beamline for Extreme Fields (HIBEF) at the European XFEL, could help researchers to understand the
many planets we already know about outside our solar system to ascertain whether life might even be possible on any of them.

Fusion experiments could benefit practically from the new measuring
method, as well. Fusion research also tries to recreate on Earth
processes that occur under great pressure in stars. During inertial
confinement fusion, deuterium and tritium fuels are heated to extremes
and compressed -- warm dense matter is an intermediate state. With the
help of X-ray scattering, this process could be monitored precisely.


========================================================================== Story Source: Materials provided by
Helmholtz-Zentrum_Dresden-Rossendorf. Note: Content may be edited for
style and length.


========================================================================== Journal Reference:
1. S. Frydrych, J. Vorberger, N. J. Hartley, A. K. Schuster,
K. Ramakrishna,
A. M. Saunders, T. van Driel, R. W. Falcone, L. B. Fletcher,
E. Galtier, E. J. Gamboa, S. H. Glenzer, E. Granados,
M. J. MacDonald, A. J.

MacKinnon, E. E. McBride, I. Nam, P. Neumayer, A. Pak, K. Voigt,
M. Roth, P. Sun, D. O. Gericke, T. Do"ppner, D. Kraus. Demonstration
of X-ray Thomson scattering as diagnostics for miscibility in warm
dense matter.

Nature Communications, 2020; 11 (1) DOI: 10.1038/s41467-020-16426-y ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200624103259.htm

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