Title: Building a high-temperature spectral library to interpret Lava Worlds

Abstract:  Rocky exoplanets with dayside temperatures exceeding 1500 K can sustain molten or partially molten surfaces. These “lava worlds” preserve information on planetary composition, magmatic processes, and the early evolution of rocky planets. However, the interpretation of their InfraRed (IR) spectra observed by space telescopes critically depends on high-temperature reference data, which have so far been lacking. We present new results from a recently developed analytical setup that enables in situ measurements of spectral emissivity for solid and molten planetary analogs up to 2000 K, over the 1–25 µm range, conditions directly relevant to lava worlds. We obtained high-temperature spectra of representative silicate compositions ranging from basaltic to rhyolitic endmembers (33–89 wt. % SiO₂). The results highlight the complexity of radiative properties at high temperature by revealing the systematic variations of emissivity with temperature, wavelength, and composition, while also demonstrating that small differences in bulk chemistry or microstructure can produce strong spectral contrasts. To evaluate observational implications, we model planet-to-star fluxes based on these emissivity datasets and show how spectral features may be detected with James Webb Space Telescope. These measurements provide the first step toward reliably connecting exoplanet observations to plausible surface and interior processes. By linking high-temperature laboratory spectra to telescope observation data, our work establishes a foundation for interpreting the surfaces of lava worlds, constraining their geological diversity, and refining models of rocky planet formation in extreme environments.