Karl G. Jansky Very Large Array (VLA) Plains of San Augustin, west of Socorro, New Mexico		Atacama Millimeter/submillimeter Array (ALMA) Atacama Desert, Chile

VLA RADIO MAPS OF SATURN WITH THE UPGRADED VLA

a) Radio image of Saturn at a wavelength of 2 cm (Ku band, 12- 18 GHz). The color range is set from 100K to 160K to highlight Saturn's radio bands. b) The same image as in panel a), but here the color is set from -3 K to 20 K to show the structure of the rings. The yellow ellipses on the lower left of each panel indicate the synthesized beam sizes and corresponding position angles. (Zhang, Z., Hayes, A. G., de Pater, I., Dunn, D. E., Janssen, M. A., Nicholson, P. D., Cuzzi, J. N., Butler, B., Sault, R.J., Chatterjee, S., 2019. VLA multi-wavelength microwave observations of Saturn's C and B rings. Icarus, 317, 518-548.)

Images of Saturn's microwave emission reveal, in addition to the planet itself, its rings. Using data from the upgraded VLA,this figure shows the rings and planet in exquisite detail. The planet itself is visible through its thermal emission, and displays zones and belts as on Jupiter. Surrounding the north pole one can discern a hexagonal pattern, which has been seen at many other wavelengths, and both by the Voyager (1981) and Cassini (2004-2017) spacecraft. This pattern is the meandering path of an atmospheric jet stream. The hexagon itself remains nearly stationary in the rotating frame of Saturn, and has been interpreted as a westward (retrograde) propagating Rossby wave (Allison et al. 1990). The emission from the planet's rings is dominated by Saturn's thermal radiation reflected off the ring particles. Only a small fraction of the radiation at centimeter wavelengths is thermal emission from the rings themselves. Water ice comprises the bulk of Saturn's rings, yet it is the small fraction of non-icy material that is key in reveal- ing clues about the system's origin and age. Using the Monte Carlo Simrings package (Dunn et al. 2002) to fit multi-wavelength (0.7-13 cm) VLA and 2-cm Cassini/RADAR data of the rings, Zhang et al. (2017, 2018) show that the non-icy fraction of the rings varies from 0.1-0.5% in the B ring, to 1-2% in the C ring, and that the particles overall are quite porous (75%-90%, depending on location in the rings). They further showed that there is a band in the middle C ring where the intrinsic thermal emission is almost constant with wavelength, and which has an anomalously high non-icy material frac- tion (6-11%), This has been interpreted by the presence of large particles, composed of rocky cores covered by porous, icy mantles. Assuming that the non-icy fraction is due to continuous impacts by micrometeorites, the rings have been estimated to be no older than 200 Myr, while the middle C ring might have been hit by a rocky Centaur 10-20 Myr ago.

a) Image of Saturn taken by the Cassini spacecraft on 25 February 2011 about 12 weeks after a powerful storm was first detected in Saturn's north- ern hemisphere. This storm is seen overtaking itself as it encircles the entire planet. (NASA/JPL/Space Science Institute, PIA12826). b) VLA longitude-resolved map from May 2015, after subtraction of a uniform disk. As in the figure above, bight features indicate a high brightness temperature, or low NH3 abundance. Observations at X (8-12 GHz) and Ku (12-18 GHz) were combined; together they cover almost a full rotation of the planet. (Sault & de Pater; see de Pater et al., 2018.)