It’s a good time to be a fan of Europa: scientists continue to announce new insights into this distant, icy world. And this time, the results come from more than a decade of radio study of Europe.
The findings, presented at the 248th meeting of the American Astronomical Society, suggest that the way Europa’s surface scatters radio waves is clearly different from those observed on rocky worlds. In general, the data are consistent with the important radar study of Europe, which took place between the years 1980 and 1990. However, the latest observations are “more numerous and cover a much broader rotational phase of Europe,” Tunhui Xie, a doctoral student at the University of California, Los Angeles, who participated in the work, explained during the presentation.
Distant frozen worlds
Jupiter, the largest planet in our solar system, has a whopping 101 moons. But of particular interest to scientists are Europa, Ganymede and Callisto, which researchers suspect host underground oceans beneath their icy crusts. Naturally, astronomers have been paying close attention to any information they could glean from these moons. As of now, NASA’s Europa Clipper and ESA’s Juice are en route to study this neighborhood closely.
That said, there are a limited number of geological features that can tell us about something much below the surface, the National Radio Astronomy Observatory (NRAO) noted in a statement about the findings. And that’s where things like radar come in, Xie added in the NRAO statement, saying that “radio waves can penetrate ice and carry information about its internal structure and purity,” Xie added.
As the waves bounce
The new study analyzed 13 years of data collected between 2011 and 2024. One fascinating observation concerned Europa’s radar albedo, which is a measure of how bright the moon appears on radar. Specifically, Europa’s radar albedo was much higher than that of planets and rocky worlds. The way Europa scattered the radar signal looked a lot like a “distinctive multiple scattering signature within clean, porous ice,” the NRAO explained.
Additionally, the team confirmed that Europa’s radar brightness remained more or less constant, even with changes in the viewing angle between the transmitter, Europa and receiver. This trend allowed the team to effectively set a new limit on how transparent Europa’s ice will be and therefore how far below the surface radio telescopes will be able to see, the statement added. This knowledge will be key to ensuring that current and future missions to Europa make the most of their time studying the distant moon.
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