Auroral emission at Jupiter, through Juno's UVS eyes

Juno’s orbit insertion around Jupiter will take place in little bit more than one year (July 2016). After a 107-day capture orbit (Oct. 2016), it will perform a series of 33 eleven-day science polar orbits offering unprecedented views of the auroral regions of Jupiter. The science payload of Juno includes an UltraViolet Spectrograph (UVS) that will characterize the UV auroral emissions of Jupiter over all science orbits. It will obtain high-resolution images and spectra that will provide context for Juno’s in situ particles and fields measurements in the larger polar magnetosphere with Juno’s JADE and JEDI detectors. At the same time, the MAG instrument will accurately constrain magnetic field models, which will provide the connection between Juno and its field line footprint in the Jovian aurora.

The UVS instrument consists of a solar blind MCP detector with a “dog-bone” shape FOV of 0.2°x2.5°+0.025°x2°+0.2°x2.5° providing a spatial resolution of 125 km from 1RJ above the aurora and a spectral resolution of ~0.5 nm (~2 nm for extended sources). It is sensitive to EUV-FUV radiation ranging from 70 nm to 205 nm. Juno is a spin-stabilized spacecraft and is rotating at a frequency of 2 RPM. UVS will take advantage of this motion to scan the auroral regions in the direction perpendicular to the slit, while its steerable pickup mirror (±30° from the spin plane) will make it possible to point at specific regions of the aurora. Juno’s highly eccentric science orbits have a perijove close to 1.05 RJ (~5000 km above cloud deck) and an apojove at ~38 RJ. These orbits approximately lie in the Dawn meridian plane and are such that each successive pass is at a Jovian longitude displaced by 204° from the previous perijove. At perijove, Juno’s velocity will be ~60 km/s and about 20 km/s above the poles, meaning that the spacecraft will move over the northern and southern auroral regions in approximately two hours.

In this study, we are using existing HST STIS time-tag sequences of Jupiter’s UV aurorae in order to simulate the expected measurements through UVS FOV along Juno’s predicted trajectory. The simulations account for realistic instrumental specifications and pointing and for the temporal and spatial variability of the aurora. We show the results of image reconstruction obtained from scanning the auroral region with UVS slit and provide some limits on the expected data quality as a function of the location of Juno along its orbit. We also suggest portions of the science orbits for which supporting HST observations will be necessary.