Subproject 9: Experimental study of planetary ices at high pressure using dynamically-driven diamond anvil cells

PIs: H. Marquardt and H-P. Liermann, PhD: A. S. J. Mendez

Planetary ice compounds (e.g. H2O, CH4, NH3) constitute large parts of solar giant ice planets and are likely abundant in the interiors of recently discovered exoplanets. The physical properties and phase diagrams of these compounds at the pres- sure and temperature conditions of planetary interiors are poorly understood. Previous experimental studies using x-ray diffraction in static diamond-anvil cells were limited to comparably low pressures as a result of experimental difficulties related to the small scat- tering efficiency of these low-Z compounds and weakening of the high-pressure cell resulting from reactions with the sample materials. In the proposed research, we will employ re- cently developed dynamically-driven diamond-anvil cells (dDAC and mDAC) to compress planetary ice compounds on short time scales (milliseconds to seconds). The rapid com- pression will prevent chemical reactions and will allow for reaching pressures that were previously not accessibly by experiments. During compression, we will probe the samples by x-ray diffraction to study their structure, phase stability and equations of state. Such fast diffraction experiments have only recently become possible with the development of new superfast detectors. Initial experiments will be performed at the Extreme Conditions Beamline at PETRA III, DESY. During the course of the project, we will start performing experiments at the High Energy Density instrument at the European XFEL that will be- come available to users in 2018. The results of our experiments will provide new insights to the stability fields and physical properties of planetary ice compounds in the interiors of solar giant ice planets and exoplanets. The results will also provide key anchor points to constrain computational predictions (carried out in SP3) and serve as input parameters for large-scale numerical models to simulate the dynamics of planets (collaboration with SP4/SP5).

Approximate P-T-conditions that have been reached by previous XRD experiments to characterize structure and compression behavior of molecular planetary solids using static DACs are shaded in blue. The target P-T-space for the here-proposed dynamically-driven DAC experiments is indicated by the red shaded area. For comparison, Earth’s geotherm is shown along with the ice giant planets’ adiabats [Redmer (2011)] and predicted mini-Neptune (GJ 876d, 7.5 times the Earth mass) P-T-conditions [Valencia (2007)], assuming a planet that contains an ice-layer covering a terrestrial core (40% by mass stored in different forms of planetary ices). Some key scientific questions are highlighted that will be addressed by the proposed research (stars, bars to illustrate possible pressure regions).
(left) Sizes and orbital periods of candidate planets found by NASA’s Kepler mission. (right) Potential mini-Neptune composition (illustrations modified from NASA).

Contact PIs

Dr. Hauke Marquardt, Universität Bayreuth, Bayrisches Geoinstitut (BGI)
Universitätsstr. 30, 95440 Bayreuth
T: +49 (0)921 55 37 18, Email

Dr. Hanns-Peter Liermann, Deutsches Elektronen Synchrotron (DESY)
Notkestr. 85, 22607 Hamburg
T: +49 (0)40 899 85 722, Email

Dr. Emma Elizabeth McBride, European XFEL GmbH
Notkestr. 85, 22607 Hamburg
T: +49 (0)40 899 85 754, Email