Scientists decode radar signatures of moons of Jupiter and Saturn

A senior scientist at the Southwest Research Institute, Dr. A joint study led by Jason Hofgartner sheds light on the startling radar signatures of icy moons orbiting Jupiter and Saturn. The distinctive radar features of these celestial bodies, which differ significantly from the characteristics of the rocky planets and most of Earth’s ice, have long puzzled researchers.

“Six different models have been published to explain the radar signatures of icy moons orbiting Jupiter and Saturn,” said Hofgartner, first author of the study, published in Nature. Astronomy. “The way these objects scatter radar is significantly different from rocky worlds like Mars and Earth, and smaller objects like asteroids and comets.”

“When we look at Earth’s moon, it looks like a round disk, even though we know it’s a sphere. Planets and other moons also look like disks in telescopes,” Hofgartner said. “During radar observations, the center of the disk becomes very bright and its edges much darker. The changes from center to edge are very different from rocky worlds for these icy moons.”

Hofgartner of NASA’s Jet Propulsion Laboratory, Dr. He says, in collaboration with Kevin Hand, the extraordinary radar properties of these satellites, such as reflectivity and polarization (the direction of light waves as they travel through space), are very likely to be explained. using the coherent backscatter effect (CBOE).

“When you’re in the opposite position, the surface appears much brighter than it would normally be when the Sun is directly behind you, in the line between you and the object,” Hofgartner said. “This is known as the opposition effect. When it comes to radar, the emitter replaces the Sun and the receiver replaces your eyes.”

Hofgartner explained that an icy surface has a stronger opposing effect than a normal surface. For every scattering path of light reflected from ice, there is a path in the opposite direction in the opposite direction. Since the two paths are exactly the same length, they combine in harmony to provide additional lighting.

In the 1990s, studies were published that claimed the CBOE was the explanation for the anomalous radar signatures of icy satellites, but that other explanations could explain the data equally well. Hofgartner and Hand developed the polarization definition of the CBOE model and also showed that the modified CBOE model is the only published model capable of describing all ice satellite radar characteristics.

“I think this shows us that the surfaces and meters of depth of these objects are very damaged,” Hofgartner said. “They’re not so monotonous. Icy rocks dominate the landscape, perhaps like the chaotic mess after a landslide. This explains why the light is reflected in so many different directions, giving us these unusual polarization signatures.”

Hofgartner and Hand used radar observations from the Arecibo Observatory, one of two telescopes that conducted radar observations of icy satellites until its support structure, antenna, and dome were severely damaged by collapse, after which it was decommissioned. The researchers hope to make more observations as possible and plan to examine radar studies of polar ice on Mercury, the Moon and Mars, along with additional archival data that may shed more light on icy moons and the CBOE.