X-Ray Vision Into The Planet's Interior

DFG supports interdisciplinary research project with two million euros

With the help of telescopes on Earth and the universe, several thousand planets have already been discovered outside our solar system since 1996. However, the observation data such as mass, radius and distance to the central star only reveal a few details about the structure and development of these exoplanets. The research group "Matter in the Interior of Planets" under the leadership of the University of Rostock, in which scientists from DESY are also involved, wants to find out more about these planets within the framework of a project funded by the German Research Foundation (DFG). The interdisciplinary cooperation includes theory, modeling and experiments. This also includes the experimental investigation of extreme states of matter as they occur in the interior of planets.The DFG initially supports the project for about three years with around two million euros.

"One of the strengths of our application is that it combines theory, modeling, and experimentation to explore the construction and evolution of planets within and outside our solar system," explains Prof. Ronald Redmer of the University of Rostock and spokesman of the research group. In addition, the findings should be used in the evaluation of observation data from satellite emissions.

With the NASA space telescope "Kepler" a lot of planets in the range between one and twenty earth masses on short orbits around sunlike stars were discovered. One differentiates so-called Supererden with up to ten earth masses and densities similar to the Earth as well as neptune-similar planets, which have a similar density as the named planet Neptune in our solar system. Neptune has a solid core surrounded by a jacket of liquid water, ammonia and methane as well as an atmosphere of hydrogen, helium and methane. Inside all these planetary types prevail pressures which can be several times higher than in the Earth's interior, and temperatures of several thousand degrees Celsius. The researchers now want to find out how the main components of the planets - for example the silicates and magnesium oxide typical for Supererden as well as so-called planetary ice such as water, methane and ammonia in neptune-like planets - behave under these conditions.

At the so-called Extreme Conditions Beamline (ECB) at DESY's high-intensity X-ray source PETRA III, material samples can be illuminated at high pressures and temperatures. "The Extreme Conditions Beamline is ideally suited to investigate the structure of magnesium oxide and silicates as well as planetary iron by means of X-ray diffraction under the pressure and temperature conditions of the planet's interior," explains DESY researcher Hanns-Peter Liermann, beamline manager of ECB and Ko -Project leader for two applications of the research group. "To produce a pressure of four to ten million atmospheres and temperatures of more than 4500 degrees, we will use new types of so-called diamond stamped cells in which resistive heating and laser radiation are heated."

Diamant stamp cells (DAC) compress the sample between two small diamonds with extremely high pressure. For the investigation of oxides and silicates, the researchers use the so-called Double Stage DAC (dsDAC), developed by Leonid Dubrovinsky of the Bavarian Geoinstitut at the University of Bayreuth (head of this subproject), which with around ten million atmospheres the highest static pressures in metals worldwide Can be generated. "In order to elucidate the structure of oxides and silicates under these high pressures, a very fine X-ray beam is needed since the compressed sample between the two diamonds is very small," explains Liermann. Both the ECB and the nanofocussing beamline P06 offer this beam to PETRA III.

Planetary ice, on the other hand, is examined in a dynamic diamond stamped cell (dDAC) for its structure, which can produce a pressure of up to four million atmospheres. "We will carry out our experiments on extremely short time scales and thus achieve unprecedented pressures and temperatures," explains Hauke ​​Marquardt from the Bavarian Geoinstitute, head of this subproject. In order to be able to carry out the experiments quickly, Marquardt and Liermann will use the strong and focused x-ray beam of the ECB.

During the second half of the project, the scientists involved will also carry out the structural studies on the High-Energy-Density Instrument (HED) of the European X-ray laser, which is currently being put into operation. With its ultrasound flashes, it is intended to make it possible to clarify the structure of the planetary materials even more rapidly - and thus before the destruction of the diamonds in the stamp cell - by means of the technique of X-ray diffraction.

In addition to the universities in Rostock and Bayreuth, the European XFEL and DESY, the Berlin Institute for Planetary Research at the German Aerospace Center (DLR) is also involved in the research group.