Glenn Research Center – NASA
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What are Icy Satellites?
Icy Satellites or call them icy rocks, that orbit around Jupiter and Saturn have made scientists curious and perplexed due to their difference in features and properties from the rocky worlds and the ice here on Earth. Their unique radar signatures have sparked questions in the brains of scientists regarding the composition of those icy satellites.
Research by Jason Hofgartner
The Co-Author of a new study on these icy satellites namely Jason Hofgartner has said that six different models have been used to explain the unusual radar signatures that emanate from the icy satellites. He added that the way these icy satellites emanate and scatter radar is very much different from rocky worlds like earth and mars, and also very different from other celestial bodies like asteroids and comets.
Dr. Hofgartner said that when we look up to see the moon it is a circular disk even if we know that it is a sphere. Planets and other moons similarly look like disks when observed through a telescope. He said that while making radar observations the edges of the disk are dark and the center of the disk is very bright. The change from center to edge is very much different for those icy satellites than for rocky worlds.
Coherent Backscatter Opposition Effect (CBOE)
Scientists think these unusual radar signatures could be due to Coherent Backscatter Opposition Effect or CBOE. Hofgartner the Co-Author of the study said that when you’re in opposition, the sun is positioned directly behind you in the line between you and the target object of observation when this happens he said that the surface of the target object appears much brighter than it should. This is called the opposition effect, the transmitter stands in place of the sun, and a receiver in place of your eyes in the case of radar observations.
This effect is strengthened due to the ice present on the rocks. The light is scattered by the ice when it bounces through it which in turn makes the icy satellite even brighter.
Dr. Hofgartner said that the above-mentioned effect in icy surfaces tells us that the surfaces and the subsurfaces of these objects are very tortured. He said that the surfaces are not very uniform and the surfaces look very chaotic like how they look after a landslide. He said this explains the light bouncing off in different directions yielding very unusual signatures.
This work was published in Nature Astronomy. It is built on the work done in the 1990s that stated the CBOE was the possible reason for unusual radar signatures from the icy satellites. But then, scientists suggested other possible reasons for these unusual signatures. The new work is built on the model of that theory and the scientists say that CBOE is the only possible explanation that can be made to comprehend the unusual radar signatures from the icy satellites orbiting Jupiter and Saturn and explain their unique and unexpected properties.
Dr. Kevin Hand Co-Author of the study from NASA’s Jet Propulsion Laboratory and Dr. Jason Hofgartner used Arecibo Observatory to make their observation for the study. That observatory was one of only two telescopes that made radar observations on Icy satellites before it was damaged due to the collapse of its support structure destroying its antenna and dome, and it was then decommissioned. The scientists hope to make follow-up observations and also study archival data to understand more about icy satellites and CBOE as well as make observations and study the ice present on the poles of Mercury, Moon, and Mars.
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