Thermal conductivity is one of the prime material properties that rules the cooling rate of planets. In the case of Earth, for instance, thermal conductivity of its core elements tells us how long a sustainable geodynamo could have been driven through convective mechanisms. However, measuring thermal conductivity under extreme conditions is a challenging task. Static compression experiments in Diamond Anvil Cells (DAC) have been conducted using many different techniques aiming to examine this property and, in some cases, studies have provided strikingly different values. For pure iron there is, at certain pressure conditions, up to an order of magnitude difference between studies. In other words, despite extensive research to uncover the truth, even the pure element (Fe) of one of Earth’s main core components still remains loosely constrained, at relevant Earth interior conditions. Additionally, the determination of thermal conductivity at the liquid state remains majorly out of reach of present-day experimental techniques. This calls for understanding the ongoing discrepancies as well as innovation in this research field to extend the limits of detectability at extreme conditions. This talk will introduce a new approach for thermal conductivity determination, where we combine (i) temperature measurements on samples in a DAC, (ii) volumetric heating at the European X-ray Free Electron Laser (Eu-XFEL) facility and (iii) Finite Element Modelling (FEM). By adjusting the thermal conductivity in our models to approach the temperature measurements obtained from Streak Optical Pyrometry (SOP), we can constrain the material properties of the assemblage heated in a DAC. Measuring temperature at the time scales needed in this study (~2 µs time window over a µm-sized sample) is at the edge of the present-day technological capabilities but has been demonstrated feasible in initial studies at European XFEL. This technique can open up a new avenue for thermal conductivity measurements in the higher temperature and pressure ranges of planetary interiors.