Thermophysical properties of the Europa surface constrained by Galileo photopolarimeter-radiometer temperature measurements
Abstract
Context. 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. Aims. 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. Methods. We used the KRC thermal model (K refers to the conductivity κ, R to the density ρ, 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. Results. 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. Conclusions. 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.
Related
- Global thermophysical characterization of Mercury’s diurnal temperature cycle in support of BepiColombo SIMBIO-SYS
- Gaia DR3 Compact Binary Candidates Constrained by Radial Velocity Measurements
- Rates of tidal disruption events from constrained cosmological simulations of the local Universe: population properties and implications for transient surveys
- Fundamental effective temperature measurements for eclipsing binary stars - IX. Characterisation of 5 solar-type sclipsing binaries with M-dwarf companions
- The AURORA Survey: High-redshift Empirical Metallicity Calibrations from Electron Temperature Measurements at z = 2–10
BibTeX
@article{lange2026thermophysical,
title = {{Thermophysical properties of the Europa surface constrained by Galileo photopolarimeter-radiometer temperature measurements}},
author = {Lucas Lange and Sylvain Piqueux and P O Hayne and Cyril Mergny and Alice Le Gall and Frédéric Schmidt and Julie Rathbun and John Spencer and Tom Nordheim and Kya Sorli and Sarah Howes and Carly Howett and Christopher S Edwards and Philip R Christensen},
journal = {Astronomy \& Astrophysics - A\&A},
year = {2026},
month = sep,
doi = {10.1051/0004-6361/202660450},
url = {https://hal.science/hal-05755154v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Thermophysical properties of the Europa surface constrained by Galileo photopolarimeter-radiometer temperature measurements
AU - Lucas Lange
AU - Sylvain Piqueux
AU - P O Hayne
AU - Cyril Mergny
AU - Alice Le Gall
AU - Frédéric Schmidt
AU - Julie Rathbun
AU - John Spencer
AU - Tom Nordheim
AU - Kya Sorli
AU - Sarah Howes
AU - Carly Howett
AU - Christopher S Edwards
AU - Philip R Christensen
PY - 2026
DA - 2026/09/10
JO - Astronomy & Astrophysics - A&A
DO - 10.1051/0004-6361/202660450
UR - https://hal.science/hal-05755154v1
AB - Context. 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. Aims. 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. Methods. We used the KRC thermal model (K refers to the conductivity κ, R to the density ρ, 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. Results. 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. Conclusions. 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.
SN - 0004-6361
SN - 1432-0746
ER -