![(Top) Measured OC albedo values from Goldstone (from Table 4) and (bottom) measured OC albedo values from the GBT (from Table 5). The horizontal dashed lines indicate the weighted means of the albedos, which is 0.90 for Goldstone and 0.80 for GBT. The error bars on our albedo values are taken to be the total uncertainty calculated in Section 4. The color bar on the right shows the dates of our observations in YYMMDD. The x-axis is the subradar point west longitude. -- [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/08/Radar-observations.png?fit=1200%2C711&ssl=1)
[astro-ph.EP] Three of Jupiter’s Galilean satellites – Europa, Ganymede, and Callisto – are of particular scientific interest due to their icy shells and suspected subsurface oceans.
However, the radar properties of the icy satellites have not been measured since observations in 1987-1991. Because radio waves can penetrate pure ice to considerable depths, radar observations provide a powerful means of characterizing the subsurface properties of the icy shells of these satellites, offering key insights into planetary evolution.
We have observed Europa using the Goldstone 3.5-cm Solar System Radar and the Green Bank Telescope (GBT) in 2011-2024 in order to address a longstanding gap in the radar studies of these moons. In this paper, we present the most longitudinally comprehensive set of radar measurements of Europa to date and describe its disk-integrated radar properties.
On the basis of monostatic Goldstone data, we find radar albedo values in two circular polarizations of σ̂ OC = 0.92 ± 0.11 and σ̂ SC = 1.35 ± 0.13 (unweighted mean and root-mean-square dispersion), with a circular polarization ratio of μc = 1.44 ± 0.12 (weighted mean and root-mean-square dispersion). Values obtained bistatically at the GBT are similar.
The μc values suggest a leading-vs-trailing side dichotomy in radar scattering properties on Europa. Our results support the existence of the coherent backscatter opposition effect (CBOE), currently the most widely accepted physical mechanism that explains the unusual radar scattering properties of the icy Galilean satellites.
Because we observed Europa with a bistatic configuration, we can place a lower bound on the width of Europa’s CBOE peak equal to 36 arcsec, which provides an upper bound of 32 m (∼1000 wavelengths) on the penetrating depth of X-band radar waves at Europa.
Tunhui Xie, Jean-Luc Margot, Sebastiano Padovan, Frank Ghigo, Will Armentrout, Joseph S. Jao, Jon D. Giorgini, Joseph Lazio
Comments: 31 pages, 17 figures, 8 tables, supplementary figures for the figure set and CSV files for the spectra are included as ancillary files. Accepted for publication in PSJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2608.17689 [astro-ph.EP] (or arXiv:2608.17689v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2608.17689
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Submission history
From: Tunhui Xie
[v1] Tue, 18 Aug 2026 12:02:59 UTC (4,789 KB)
https://arxiv.org/abs/2608.17689
astrobiology, astrogeology,
