Thermophysical properties of the Europa surface constrained by Galileo photopolarimeter-radiometer temperature measurements

Thermal measurements provide key constraints on the physical properties of icy satellite surfaces. On Europa, previous analyses of the Galileo Photopolarimeter-Radiometer (PPR) dataset revealed heterogeneities in thermal inertia, but the limited spatial resolution prevented a detailed thermophysical characterization. We derive high-resolution maps of the Europa surface albedo and thermal inertia and infer the microphysical properties of its icy regolith from a reanalysis of the Galileo PPR dataset by discussing the processes controlling its thermophysical evolution. We used the KRC thermal model (K refers to the conductivity ąppa, R to the density ̊ho, and C to the specific heat C) to analyze the PPR brightness temperatures and retrieve the albedo and thermal inertia. These values were then interpreted using conductivity models of porous ice to constrain the grain size and porosity. We derived a mean Bond albedo of 0.64 ± 0.06 and a mean thermal inertia of 56 ± 17 J m -2 $ K^-1 s^-1/2 (1σ). The thermal inertia shows significant spatial variations, with a low-inertia equatorial band (39 ± 7) and higher values at mid-latitudes on the leading hemisphere (56 ± 11). The trailing-hemisphere equator also exhibits higher thermal inertia (63 ± 17), likely related to compositional differences. Conductivity models indicate a porous icy regolith with grain sizes ranging from a few micrometers to a few centimeters and an average porosity of $0.61 ± 0.1 in the upper centimeters of the Europa surface. The thermal inertia distribution shows little correlation with geological units. Its agreement with modeled magnetospheric ion fluxes instead suggests that sputtering-driven sintering plays a fundamental role in shaping the thermophysical properties of Europa. The absence of a high-inertia equatorial band analogous to the PacMan anomaly on the icy moons of Saturn indicates inefficient electron-driven sintering, while temperature-gradient metamorphism might enhance grain growth at depth. The modeled surface temperatures range between ∼ 67 and 148 K at mid to low latitudes, with peak daytime values counteracting radiolytic amorphization while limiting volatile stability.