Planetary Aurorae

The radio frequency properties of Jupiter make it an ideal source for bistatic sounding of the ice shells of Jupiter's icy moons. The Jovian DAM emissions are produced near Jupiter’s magnetic pole via cyclotron emission resulting in strong (~4 MJy average) bursts of emission below the cutoff frequency of 35 MHz. The source is compact producing wideband emission in the 300 kHz - 35 MHz band and 100% polarized. The times of the strongest emissions are predictable based on the orbit phase of Io and Central Meridian Longitude of Jupiter. Observation opportunities for reflected signals off Jupiter's icy moons account for 20% of the time Jupiter is observable. Our approach is to use continual monitoring capabilities of the LWA-OVRO radio telescope to statistically probe the effect of reflections from the icy moon. Additionally, the LWA-OVRO provides calibrated Stokes V polarization measurements, which serve to disambiguate between spurious direct and reflected Jovian decametric emissions as well as characterize the dielectric properties of Jupiter’s Galilean moons.

This technique is a straightforward extension of the ground-based 2.4 GHz radar of Jupiter's Galilean satellites that began in the 1970’s. The advantage of the proposed technique is that Jupiter provides a natural "transmitter" of both higher power and lower frequency than is feasible from the ground. The lower frequencies available to LWA-OVRO are also close to the HF and VHF radar instruments proposed for JUICE and Europa Clipper mission providing valuable information or constraints on surface reflection losses. Since the source is at Jupiter and not on Earth, using the Jovian DAM provides a unique opportunity for bistatic sounding of the ice shells of Europa and Ganymede. The surface roughness and fracturing could be constrained from variations in polarization fraction as a function of incidence angle and frequency. Further insight can be gained by comparing the reflections observed from Europa, Ganymede, and Callisto.