Scientists identify possible source of ‘unusual radar signatures’ at the edge of the Solar System

The objects are also extremely bright, even in areas that would be expected to be dark

Andrew Griffin
Friday 24 March 2023 06:18 GMT
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Scientists believe they have found an explanation for “unusual radar signatures” found at the edge of the solar system.

Icy satellites that are in orbit around Jupiter and Saturn have perplexed scientists because they are so different from both rocky worlds and most ice on Earth. The markedly different radar signatures have led to questions about how they are composed.

The objects are also extremely bright, even in areas that would be expected to be dark.

“Six different models have been published in an attempt to explain the radar signatures of the icy moons that orbit Jupiter and Saturn,” said Jason Hofgartner, a co-author of the new study. “The way these objects scatter radar is drastically different than that of the rocky worlds, such as Mars and Earth, as well as smaller bodies such as asteroids and comets.”

Now scientists believe that a specific effect, known as the coherent backscatter opposition effect or CBOE, is likely to explain the extraordinary radar signatures coming back from the satellites.

“When you’re at opposition, the Sun is positioned directly behind you on the line between you and an object, the surface appears much brighter than it would otherwise,” Hofgartner said. “This is known as the opposition effect. In the case of radar, a transmitter stands in for the Sun and a receiver for your eyes.”

On an icy surface, that effect is even stronger. Light is scattered as it bounces through the ice, which brightens it further.

“I think that tells us that the surfaces of these objects and their subsurfaces down to many meters are very tortured,” said Dr Hofgartner. “They’re not very uniform. Icy rocks dominate the landscape, perhaps looking somewhat like the chaotic mess after a landslide. That would explain why the light is bouncing in so many different directions, giving us these unusual polarization signatures.”

The work is described in an article, ‘An icy-satellite radar-properties continuum that requires the coherent backscatter effect’, published in Nature Astronomy today.

It builds on work published in the 1990s that suggested CBOE as an explanation for those unusual radar signatures. Then, researchers suggested other explanations could account for the strange data.

But the new work builds on the model behind that theory and the researchers claim it is now the only process that would explain all of the different and unexpected properties of the satellites.

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