XFEL: DFG funds investigation of exoplanets at European XFEL

With the help of telescopes on Earth and in space, several thousand planets outside of our solar system have been discovered since 1996. Observation data such as mass, radius, and distance from their central star give only a few details about the composition and origin of these exoplanets. The research unit “Matter Under Planetary Interior Conditions”, led by the University of Rostock and including scientists from European XFEL will find out more about these planets in the framework of a grant funded by the German Research Foundation (DFG). The researchers want to draw inferences about exoplanets based on the planets in our own solar system and develop suitable methods for this purpose. Their interdisciplinary collaboration comprises theory, planetary modelling, and experiments. This comprises experimental investigations of materials under extreme conditions, such as those found inside of planets at, among others, the European XFEL and the research centre DESY. The DFG will fund the project for the next three years with a total contribution of around 2 million euro.

“A strength of our proposal is that it combines theory, planetary modelling, and experiments in order to learn more about the composition and development of planets inside and outside of our solar system”, says Prof. Ronald Redmer of the University of Rostock, spokesperson for the research unit. In addition, the findings will be used for the evaluation of observation data from satellite missions.

 The Kepler Space Telescope has discovered a large number of planets between one and twenty times the mass of the Earth in orbits close to Sun-like stars. These exoplanets are defined as so-called “super-Earths”, which have a similar density and masses up to ten times that of the Earth, and neptunian planets, which have a similar density as the planet Neptune in our solar system. Neptune has a solid core; a mantle composed of liquid water, ammonia, and methane; as well as an atmosphere made of hydrogen, helium, and methane. In the interiors of all of these types of planets pressures can be many times higher than those inside the Earth and temperatures can reach several thousand degrees Celsius. The researchers want to find out how the principal constituents of these planets—for example, magnesium oxide and silicates for super-Earths as well as water, methane, and ammonia for neptunian planets—behave under these conditions.

The High Energy Density Science instrument at the European XFEL, or HED for short, enables experimental investigations of extreme states of matter like those found inside of planets. “In the course of these experiments, we can generate brief spikes in pressure up to a million bar on the sample”, explains Karen Appel, a scientist at HED and project leader for this part of the research unit’s proposal. “The pressure would be as strong as having the weight of the world’s tallest building, the Burj Khalifa in Dubai, on someone’s fingertip.” The high pressures and temperatures at the HED instrument are generated through a shockwave triggered by an intense laser pulse. If the material decompresses after the shock, it goes through many different combinations of pressures and temperatures with distinctive material characteristics within very small fractions of a second. The short light flashes of the European XFEL enable sharp snapshots of these states and their properties to be taken. “Through X-ray scattering and X-ray spectroscopy, we will be able to determine the time-resolved structure and properties of magnesium oxide and silicates under these conditions”, says Appel. “With that, we can gather essential data for planetary modelling.”

Other than the Universities of Rostock and Bayreuth and European XFEL, DESY and the DLR Institute for Planetary Research in Berlin are also participating.