Study suggests explanation for unusual radar signatures of icy satellites in the outer solar system

A examine co-authored by Southwest Analysis Institute Senior Analysis Scientist Dr. Jason Hofgartner explains the weird radar signatures of icy satellites orbiting Jupiter and Saturn. Their radar signatures, which differ considerably from these of rocky worlds and most ice on Earth, have lengthy been a vexing query for the scientific neighborhood.

“Six totally different fashions have been printed in an try to clarify the radar signatures of the icy moons that orbit Jupiter and Saturn,” stated Hofgartner, first creator of the examine, which was printed this month in Nature Astronomy. “The way in which these objects scatter radar is drastically totally different than that of the rocky worlds, equivalent to Mars and Earth, in addition to smaller our bodies equivalent to asteroids and comets.”

The objects are additionally extraordinarily brilliant, even in areas the place they need to be darker.

“After we lookup at Earth’s moon it seems like a round disk, though we all know it is a sphere. Planets and different moons equally seem like disks by means of telescopes,” Hofgartner stated. “Whereas making radar observations, the middle of the disk could be very brilliant and the sides a lot darker. The change from middle to edge could be very totally different for these icy satellites than for rocky worlds.”

In collaboration with Dr. Kevin Hand of NASA’s Jet Propulsion Laboratory, Hofgartner argues that the extraordinary radar properties of those satellites, equivalent to their reflectiveness and polarization (the orientation of sunshine waves as they propagate by means of space) could be very prone to be defined by the coherent backscatter opposition impact (CBOE).

“Whenever you’re at opposition, the Solar is positioned immediately behind you on the road between you and an object, the floor seems a lot brighter than it might in any other case,” Hofgartner stated. “This is called the opposition impact. Within the case of radar, a transmitter stands in for the Solar and a receiver on your eyes.”

An icy floor, Hofgartner defined, has an excellent stronger opposition impact than regular. For each scattering path of sunshine bouncing by means of the ice, at opposition there’s a path within the actual other way. As a result of the 2 paths have exactly the identical size, they mix coherently, leading to additional brightening.

Within the Nineteen Nineties, research had been printed stating that the CBOE was one rationalization for the anomalous radar signatures of icy satellites, however different explanations may clarify the information equally properly. Hofgartner and Hand improved the polarization description of the CBOE mannequin and in addition confirmed that their modified CBOE mannequin is the one printed mannequin that may clarify all the icy satellite radar properties.

“I believe that tells us that the surfaces of those objects and their subsurfaces all the way down to many meters are very tortured,” Hofgartner stated. “They are not very uniform. Icy rocks dominate the panorama, maybe trying considerably just like the chaotic mess after a landslide. That may clarify why the sunshine is bouncing in so many alternative instructions, giving us these uncommon polarization signatures.”

The radar observations Hofgartner and Hand used had been from the Arecibo Observatory, which was considered one of solely two telescopes making radar observations of icy satellites till it was severely broken by the collapse of its help construction, antenna and dome meeting and subsequently decommissioned. The researchers hope to make follow-up observations when doable and plan to check further archival knowledge which will shed much more mild on icy satellites and the CBOE, in addition to radar research of ice on the poles of Mercury, the Moon, and Mars.

The paper “An icy-satellite radar-properties continuum that requires the coherent backscatter impact,” seems in Nature Astronomy.