The icy shell of one of the most promising targets in the search for extraterrestrial life has turned out to be even more intriguing than previously thought. A 13-year radar study of Jupiter’s moon Europa has confirmed that its surface scatters radio waves with unusual intensity and complexity—quite unlike typical rocky bodies in the Solar System.
The Longest Radar Survey
Graduate student Tunhui Xie of the University of California, Los Angeles (UCLA) and her advisor, Professor Jean-Luc Margot, used NASA’s Goldstone Solar System Radar together with the National Science Foundation Green Bank Telescope (NSF GBT). From 2011 to 2024, they illuminated Europa with 3.5-centimeter radio waves and recorded the reflected signals.
The findings were presented at the 248th meeting of the American Astronomical Society in Pasadena on June 16, 2026, according to the National Radio Astronomy Observatory (NRAO). The project represents the most extensive ground-based radar survey of Europa ever conducted, filling a 30-year gap since the previous observing campaign carried out between 1987 and 1991.
A Mirror of Ice
Europa’s radar albedo—that is, the ability of its surface to reflect radio waves—turned out to be significantly higher than that of typical planets and asteroids. The reflected signal retained the same circular polarization as the transmitted beam. This is a sign of multiple scattering within pure, porous ice.
This behavior is explained by the coherent backscattering effect. Radio waves are reflected multiple times inside the icy shell before returning to the receiver, and this process dramatically amplifies the echo. Similar radar properties have been observed in Jupiter’s two other Galilean moons, Ganymede and Callisto, consistent with models of very pure water ice and increases the likelihood of ice shells and potential subsurface oceans on all three bodies.
Bistatic configuration
The researchers used a bistatic observation setup. The Goldstone antenna transmitted the signal, which was received simultaneously by both the Goldstone antenna and the Green Bank telescope. This made it possible to test how the coherent backscattering effect varies depending on the angle between the transmitter, the satellite, and the receiver.
Europa’s radar brightness remained roughly constant even as the angle increased. This means that the peak of backscattering is broader than the range of angles that could be covered during the observations. This result sets a new limit on the depth to which radio waves penetrate the ice before being absorbed and provides new insights into the internal structure of Europa’s icy shell.
Stability Over Decades
The new measurements are in good agreement with the results of the 1987–1991 campaign, which was conducted using the Goldstone radar and the now-demolished Arecibo Observatory. This stability in radar properties over decades provides a basis for interpreting ground-based and space-based measurements within a single physical framework.
The team also checked whether the radar brightness of Europa’s leading and trailing hemispheres differs. They found no statistically significant difference, but did detect a hint that the rear hemisphere might be slightly brighter in one polarization state. If confirmed, this effect could be linked to the influence of charged particles from Jupiter’s magnetosphere on the structure of the ice.
Ground-based radars provide only an averaged signal from the entire visible disk of Europa, whereas the REASON radar aboard the Europa Clipper spacecraft will be able to probe the icy crust to a depth of up to 30 km and construct a three-dimensional map of subsurface structures during each of its 49 planned flybys. As Universe Today notes, the spacecraft will arrive in the Jupiter system in April 2030 and begin its scientific mission in the spring of 2031.
