A UCLA-NRAO team has assembled the most extensive radar portrait of Europa's icy surface ever collected, spanning 13 years and two major radio facilities - and the dataset will serve as the benchmark for NASA's Europa Clipper when it arrives in 2030.
Ground-based radar observations spanning 13 years have produced the most detailed portrait yet of Europa’s ice shell - establishing a scientific baseline that NASA’s Europa Clipper mission will rely on to calibrate its own ice-penetrating radar data when the spacecraft begins detailed observations of the moon in 2030.
The findings were presented by UCLA graduate student Tunhui (Tina) Xie at a National Radio Astronomy Observatory press conference during the 248th meeting of the American Astronomical Society in Pasadena on June 16, 2026. The study was conducted by Xie and her supervisor, Professor Jean-Luc Margot at the University of California Los Angeles, with support from Will Armentrout at the NSF’s National Radio Astronomy Observatory.
“Radar delves below what is easily seen, because radio waves can penetrate into the ice and carry information about its internal structure and purity,” Xie said, according to the NRAO press release.
The campaign used 3.5-centimetre radio waves transmitted from NASA’s Goldstone Solar System Radar in California, with signals received simultaneously by both Goldstone and the NSF’s Robert C. Byrd Green Bank Telescope in West Virginia - a bistatic configuration that captured how Europa reflects radar energy from multiple viewing geometries. Observations ran from 2011 through 2024, spanning dozens of individual sessions and covering the moon across a range of orbital phases.
The previous comprehensive ground-based radar survey of Europa dates to the late 1980s and early 1990s. This new dataset is the most geometrically complete and temporally extensive since that era.
The results confirm that Europa’s radar albedo - a measure of how brightly the moon reflects radar energy - is substantially higher than typical planets and asteroids. According to the NRAO announcement, the returning signals show strong circular polarisation that matches the transmitted beam, a signature of what scientists call the coherent backscatter opposition effect.
The mechanism works as follows: transmitted radio waves penetrate into the ice and scatter multiple times within its granular, relatively porous structure before returning toward the telescope. Rather than scattering randomly in all directions, a portion of the reflected energy retraces the path of the incoming wave and returns with concentrated intensity. This behaviour, according to Xie and Margot, is characteristic of ice that is unusually pure and free of contaminants close to the surface.
Radar brightness across the 13-year span remained remarkably consistent - both over time and across different longitudes of the moon’s surface. That stability allowed the team to place new constraints on how deeply 3.5-centimetre radio waves penetrate the ice before their signal degrades. The dataset also revealed a tentative brightness asymmetry between Europa’s leading and trailing hemispheres, though the team noted this difference was not statistically conclusive and will require further observations to confirm.
The scientific payoff of the survey extends beyond its immediate results. NASA’s Europa Clipper spacecraft, launched in October 2024, is on course to begin detailed flybys of Europa around 2030. One of its primary instruments is REASON - Radar for Europa Assessment and Sounding: Ocean to Near-surface - an ice-penetrating radar designed to map the thickness and structure of Europa’s ice shell and search for evidence of any liquid water beneath it.
“Future planetary science and space flight missions could benefit from this radar science,” Armentrout said in the NRAO release. The 13-year ground-based characterisation, he noted, gives scientists the clearest possible picture of the radar properties that REASON will encounter from orbit.
The practical implication is straightforward: interpreting what REASON sees requires knowing what “normal” Europa ice looks like at radar wavelengths. The Xie-Margot dataset provides that reference.
Europa has been a sustained focus of astrobiological interest for decades. The moon is widely believed, based on magnetic field measurements by NASA’s Galileo spacecraft and theoretical modelling of tidal heating, to harbour a liquid-water ocean beneath several kilometres of ice. Tidal forces generated by Jupiter’s gravity repeatedly flex the moon’s interior, generating heat sufficient to maintain liquid water even in the outer solar system.
Whether that ocean - if it exists - could support conditions relevant to life is an open question. It is a question that Europa Clipper’s instrument suite is specifically designed to investigate. The newly assembled radar dataset represents the most complete characterisation of the target ice shell that scientists have had to work with before that investigation begins.
The AAS 248 presentation marks the formal public release of the 13-year observational record. The abstract, submitted to the 248th American Astronomical Society meeting, is listed as Abstract #481 in the conference programme.
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