Average Ultraviolet and X-ray Auroras at Jupiter from Juno-UVS and Chandra-HRCI Data

Abstract:

The Juno spacecraft’s polar orbit provides an excellent vantage point for observing Jupiter’s auroral emissions. These emissions often include flares at far-ultraviolet (FUV) wavelengths, which have been associated with X-ray bursts. During 2017-2019, coordinated Juno-UVS and Chandra HRC-I observations were acquired during nine Juno perijoves to further investigate the connection between Jupiter’s FUV and X-Ray auroras. The X-rays are found to generally correspond with the so-called “active region” of the FUV aurora. As the X-rays are thought to represent tracers of ion precipitation, it is likely that they, and the active region of FUV emissions, are a signature of the return current that is the counterpart to the outward current (from Jupiter) associated with electron precipitation in Jupiter's main auroral oval. Simultaneous in-situ observations of precipitating O⁺ ions made by Juno-JEDI along Juno’s magnetic footprint provide support for this connection. Using the best UVS data from each of Juno’s completed perijoves, we have created average maps for the northern and southern auroras of Jupiter. While individual maps for each perijove exhibit a great variety of auroral forms and represent many different levels of activity, the average maps allow fainter (but persistent) features to stand out. The average FUV auroral brightness maps use ~1000 minutes of near-perijove Juno-UVS observations at each pole, from a wide variety of local times. Similarly, we also created average X-ray aurora maps, using ~137 hours of HRC-I observations, but only from a local time near noon. From these data we find that the average total northern FUV (X-Ray) aurora is 1.11 (1.40) times brighter than the average total southern aurora, while for the fraction of FUV (X-Ray) emissions poleward of M=30, the northern aurora is 1.33 (1.76) times brighter than the southern aurora. In the northern aurora, FUV (X-Ray) emissions poleward of M=30 account for 49.6% (63.2%) of the total northern emissions, while in the southern aurora, FUV (X-Ray) emissions poleward of M=30 account for 41.3% (50.5%) of the total southern emissions. These and other results will be compared with previous estimates of average Jovian auroral properties.