Simulating Europa’s Surface Properties with an Advanced 3D Thermophysical Model

Temperature is a fundamental quantity that drives diverse processes on the surfaces and in the interiors of planetary bodies. Conversely, measurements of surface temperatures and thermophysical properties can reveal records of both endogenic and exogenic processes. For example, surface temperatures on icy satellites may be elevated due to localized heat flow anomalies (“hot spots”) at the sources of plumes. Hot spots on Europa are expected to persist for thousands of years after the cessation of any plume activity [1]. On a global scale, interactions with the Jovian magnetosphere may cause thermophysical variations on Europa like those observed on the saturnian satellites Tethys and Dione [2, 3]. Thus, understanding Europa’s geological evolution depends on accurate knowledge of surface and subsurface temperatures. 

The NASA Europa Clipper mission will carry the Europa Thermal Emission Imaging System (E-THEMIS), a multi-band infrared radiometer, which will measure surface temperatures globally at kilometer scales and locally at decameter scales [4]. In addition to E-THEMIS, other Clipper investigations will rely upon accurate knowledge of Europa’s surface and subsurface temperatures. For example, temperature is a critical parameter in modeling radar signal propagation (i.e., REASON on Clipper and its counterpart, RIME on JUICE), as well as plasma interactions with the ice shell (e.g., the PIMS instrument on Clipper). Currently, thermophysical models lack key capabilities needed to enable this important science. 

We are developing an advanced 3D ray-tracing thermophysical model for Europa that will support achieving Europa Clipper’s interdisciplinary science goals. The model is designed to simulate effects known or expected to influence thermal infrared measurements, such as topography, albedo variations, and thermophysical properties varying at sub-km scales. Jupiter eclipses are included, as are reflected solar and emitted infrared radiation from Jupiter. We use the global Bond albedo map of Europa from [5], interpolated to match the mesh resolution. Our model implements advanced computational features, such as hardware-accelerated ray tracing using Intel Embree, SIMD/AVX-512 vectorization, and multiprocessing. Benchmark tests indicate speeds ~104 times faster than earlier versions of the model without these features. Global models with ~1 km spatial resolution (107 triangular mesh elements) can be run over a complete 3.55-day Europa diurnal cycle on a 24-core Intel Xeon workstation in < 10 minutes. This computational efficiency enables rapid exploration of the model parameter space, which will be needed to fit the E-THEMIS data by constraining thermophysical properties (e.g., thermal inertia, regolith thickness, porosity, heat flow). 

Preliminary model results (Figs. 1 & 2) demonstrate the capabilities of the model and highlight several important results: 1) Europa’s maximum surface temperatures are strongly influenced by albedo variations, 2) Peak temperatures on the sub-Jovian hemisphere drop by up to ~30 K during eclipses, and 3) The polar regions remain colder than ~90 K regardless of albedo or thermal inertia variations. Dark lineaments (i.e., the double-ridges) are among the more prominent features in the thermal maps, indicating possible feedback, which could lead to thermal segregation of dark non-ice materials [6]. Our model results also indicate that granular deposits of plume particles surrounding inactive vents may also be detectable due to their anomalous thermal emission. We will present these and other results, highlighting the possible thermophysical variations E-THEMIS and other instruments on Europa Clipper may detect.

Figure 1: Perspective view of modeled surface temperatures on Europa’s trailing hemisphere for a global thermal simulation with ~10 km/pixel resolution. The color scale ranges from 83 to 152 K. Pwyll crater (88.6°E, 25.2°S) and its ejecta are visible at the lower left in this view, which highlights the effects of albedo on surface temperatures: the brighter ejecta regions reach maximum temperatures of ~115 K, compared to ~135 K for the lower-albedo background terrain. 

Figure 2: Example diurnal surface temperature curve for the sub-Jupiter point. The ~20 K dip near local noontime is due to the solar eclipse by Jupiter, which occurs every orbit at a similar local time on the sub-Jovian hemisphere. 

References: 

[1] Abramov, O., Rathbun, J. A., Schmidt, B. E., & Spencer, J. R. (2013). Detectability of thermal signatures associated with active formation of ‘chaos terrain’on Europa. Earth and Planetary Science Letters, 384, 37-41. 

[2] Howett, C. J. A., Spencer, J. R., Hurford, T., Verbiscer, A., & Segura, M. (2012). PacMan returns: An electron-generated thermal anomaly on Tethys. Icarus, 221(2), 1084-1088. 

[3] Schaible, M. J., Johnson, R. E., Zhigilei, L. V., & Piqueux, S. (2017). High energy electron sintering of icy regoliths: Formation of the PacMan thermal anomalies on the icy Saturnian moons. Icarus, 285, 211-223. 

[4] Christensen, P. R., Spencer, J. R., Mehall, G. L., Patel, M., Anwar, S., Brick, M., ... & Rathbun, J. A. (2024). The Europa Thermal Emission Imaging System (E-THEMIS) investigation for the Europa Clipper Mission. Space Science Reviews, 220(4), 38. 

[5] Mergny, C., Schmidt, F., Andrieu, F., & Belgacem, I. (2025). A Bond albedo map of Europa. Astronomy & Astrophysics, 693, L21. 

[6] Sorli, K., & Hayne, P. (2023). Thermal Segregation as a Mechanism for Darkening Ridge Troughs on Europa. In AAS/Division for Planetary Sciences Meeting Abstracts# 55 (Vol. 55, No. 8, pp. 210-03).