Experimental studies of H20-CH4 ices in mini-Neptune exoplanets at EuXFEL

Grunddaten zu diesem Projekt

Beschreibung

Planetary ice compounds, e.g. H20, CH4, NH3 and mixtures thereof, constitute large parts of solar giant ice planets Uranus and Neptune, and are likely abundant in the interiors of recently discovered thousands of mini-Neptune exoplanets. Yet, their physical properties are poorly understood at relevant conditions (>100 GPa and >2000 K) despite being essential for planetary modelling. Previous X-ray diffraction (XRD) studies in diamond anvil cells (DAC) have been limited by the small scattering efficiency of these low-Z compounds. The extreme brilliance of X-ray beams delivered by X-ray FEL sources provide now a mean to probe the properties of elusive planetary ices at conditions previously unexplored. In this proposal, we will take advantage of new capabilities for DACs studies coupled with time-resolved X-ray diffraction diagnostics implemented at the High Energy Density (HED) instrument of the European XFEL (hereafter EuXFEL) to investigate the behaviour of ices in the H20-CH4 system. We will specifically determine the stability, structure and thermal equations of state (EoS) of superionic H20 and high pressure CH4 hydrates, including the kinetics of CH4 hydrate dissociation/formation up to 200 GPa and 5000 K. To reach the relevant high temperature conditions (> 2000 K), we will optimize a novel approach for X-ray heating of the sample with consecutive EuXFEL pulses recently introduced by our group at HED. Illumination of compressed ice samples with a pulse train will steadily increase temperature and eac.h X-ray pulse will probe the sample state induced by the previous X-ray pulse, thus enabling the rapid collection of data at increasing temperature along isochores up to melting/dissociation state. The experimental results will provide new anchor points to constrain computational predictions and serve as input parameters for large-scale numerical models to constrain the internal structure and dynamics of solar ice giants and "water-rich" exoplanets, including the origin of their anomalous magnetic fields.