Astronomers at the University of California, Los Angeles, have utilized NASA’s Goldstone Solar System Radar and NSF’s Green Bank Telescope to confirm that the icy surface of Jupiter’s moon Europa scatters radio energy in an unusually strong and complex manner, a phenomenon not observed on rocky worlds.
This artist’s impression illustrates radar waves from NASA’s Goldstone Solar System Radar penetrating Europa’s icy surface and bouncing back to be collected by the NSF’s Green Bank Telescope on Earth. Image credit: NSF/AUI/NSF’s NRAO/P.Vosteen.
Three of Jupiter’s Galilean moons, Europa, Ganymede, and Callisto, are of immense scientific interest due to their icy shells and believed subsurface oceans.
However, the radar properties of these icy satellites have not been examined since initial observations conducted from 1987 to 1991.
Since radio waves can penetrate pure ice to considerable depths, radar observations serve as a powerful tool for characterizing subsurface properties, offering crucial insights into the evolution of these celestial bodies.
“Radio waves can penetrate ice and reveal internal structure and purity, allowing radar to explore what is not easily visible,” explained Tung-Hui (Tina) Shi, a graduate student at UCLA.
To fill a long-standing research gap, Dr. Xie and Professor Jean-Luc Margot conducted observations of Europa from 2011 to 2024 using the Goldstone Solar System Radar in conjunction with the Green Bank Telescope.
These observations revealed that Europa’s radar albedo (a measure of brightness in radar) is significantly higher than that of typical planets and asteroids.
The returning radar signal exhibited the same circular polarization as the transmitted beam, a characteristic indicative of multiple scattering within clean, porous ice.
These findings lend strong support to the coherent backscattering opposition effect, which allows radio waves to bounce within the ice before returning to the telescope, greatly enhancing the echoes.
By employing a bistatic configuration—where the Goldstone radar transmits while both the Goldstone and Green Bank telescopes receive—the researchers tested how the coherent backscatter effect fluctuates with the angles between the transmitter, moon, and receiver.
The team observed that Europa’s radar brightness remained nearly consistent as the angle increased. This indicates that the bright backscatter “peak” must be wider than the sampled range of angles, thus imposing a limit on how deeply radio waves can penetrate before being absorbed.
This depth limit yields new constraints on the transparency of Europa’s ice, aiding scientists in interpreting future ice-penetrating radar data from upcoming spacecraft missions aimed at studying the moon in greater detail.
“Future planetary science and spaceflight missions, such as NASA’s Europa Clipper, could greatly benefit from these radar advances,” commented Dr. Will Armentrout, a research scientist at the NSF National Radio Astronomy Observatory supporting the radar project.
“As radar capabilities at the Green Bank Telescope continue to evolve with emerging technologies, we are excited to provide enhanced radar solutions to the scientific community.”
Authors present their findings in a result at the 248th American Astronomical Society (AAS) General Meeting taking place in Pasadena, California.
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Xie Tunhui and Jean-Luc Margot. 2026. European radar observations from 2011 to 2024: new insights into radar scattering characteristics. AAS248 Abstract #481
Source: www.sci.news