Fe and Fe alloys are the main constituents of planetary cores. Their phase diagrams under extreme conditions,however, remain poorly explored and a topic of controversies. The advent of ultrafast X-ray diffraction at the euXFEL coupled with Diamond Anvil Cell, Laser Heating, as well as X-ray heating, is opening a new exploration window for ranges of pressure, temperature and timescales. Here, we aim at quantifying melting temperatures and phase stability for pure Fe up to 300 GPa, but also more complex phase diagrams such as Fe-Si-O and its phase separation into oxides such as SiO2 and Fe-rich core materials. In addition, laser heating at the µs timescale permits to probe iron alloys with complex chemistry, such as Fe-S-O, particularly relevant for the core of Mars, before chemical migration occurs. All these experiments rely on µs timescales resolution of X-ray diffraction at the euXFEL and are not possible at more conventional LH-DAC facilities.