Proton aurora are the most commonly observed yet least studied type of aurora at Mars. In order to better understand the physics and driving processes of Martian proton aurora, we undertake a multi-model comparison campaign. We compare results from four different proton/hydrogen precipitation models with unique abilities to represent Martian proton aurora: Jolitz model (3-D Monte Carlo), Kallio model (3-D Monte Carlo), Bisikalo/Shematovich et al. model (1-D kinetic Monte Carlo), and Gronoff et al. model (1-D kinetic). This campaign is divided into two steps: an inter-model comparison and a data-model comparison. The inter-model comparison entails modeling five different representative cases using similar constraints in order to better understand the capabilities and limitations of each of the models. Through this step we find that the two primary variables affecting proton aurora are the incident solar wind particle flux and velocity. In the data-model comparison, we assess the robustness of each model based on its ability to reproduce a MAVEN/IUVS proton aurora observation. All models are able to effectively simulate the data. Variations in modeled intensity and peak altitude can be attributed to differences in model capabilities/solving techniques and input assumptions (e.g., cross sections, 3-D versus 1-D solvers, and implementation of the relevant physics and processes). The good match between the observations and multiple models gives a measure of confidence that the appropriate physical processes and their associated parameters have been correctly identified, and provides insight into the key physics that should be incorporated in future models.

Dawn storms are among the brightest events in the Jovian aurorae. Up to now, they had only been observed from Earth-based observatories, only showing the Sun-facing side of the planet. Here we show for the first time global views of the phenomenon, from its initiation to its end and from the nightside of the aurora onto the dayside. Based on Juno's first 20 orbits, some patterns now emerge. Small short-lived spots are often seen for a couple of hours before the main emission starts to brighten and evolve from a straight arc to a more irregular one in the midnight sector. As the whole feature rotates dawn-ward, the arc then separates into two arcs with a central initially void region that is progressively filled with emissions. A gap in longitude then often forms before the whole feature dims. Finally, it transforms into an equatorward-moving patch of auroral emissions associated with plasma injection signatures. Some dawn storms remain weak and never fully develop. We also found cases of successive dawn storms within a few hours. Dawn storm thus share many fundamental features with the auroral signatures of the substorms at Earth. These findings demonstrate that, whatever their sources, mass and energy do not always circulate smoothly in planetary magnetospheres. Instead they often accumulate until the magnetospheres reconfigure and generate substorm-like responses in the planetary aurorae, although the temporal and spatial scales are different for different planets.

Juno’s arrival at Jupiter in 2016 revealed unprecedented details about Jupiter’s ultraviolet aurorae thanks to its unique suite of remote sensing and in situ instruments. Here we present results from in situ observations during Juno flybys above specific bright auroral spots in Jupiter’s polar aurora. We compare data observed by Juno-UVS, JEDI, JADE, Waves, and MAG instruments when Juno was magnetically connected to bright polar auroral spots during perijove 3 (PJ3), PJ15, and PJ33. The highly energetic particles observed by JEDI show enhancements dominated by upward electrons, which suggests that the particle acceleration region takes place below the spacecraft. Moreover, both brightness and upward particle flux were higher for the northern bright spot in PJ3 compared to the southern spots found in PJ15 and PJ33. In addition, we notice the intensification of whistler-mode waves at the time of the particle enhancements, suggesting that wave-particle interactions contribute to the acceleration of particles which cause the UV aurorae. The MAG data reveal magnetic perturbations during the PJ3 spot detection by Juno, which suggests the presence of significant field-aligned electric currents. While the stable position of the bright spots in System III suggests that the phenomenon is fixed with respect to the rotation of the planet, the presence of field-aligned currents leaves open the possibility of an origin rooted much farther in the magnetosphere.

Since 2016, the Juno-UVS instrument has been taking spectral images of Jupiter’s auroras during its polar fly-bys. These observations provide a great opportunity to study Jupiter’s auroras in their full extent, including the nightside, which is inaccessible from Earth. We present a systematic analysis of features in Jupiter’s polar auroras called auroral bright spots observed during the first 25 Juno orbits. Bright spots were identified in 16 perijoves (PJ) out of 24 (there was no available data for perijove 2), in both the northern and southern hemispheres. The emitted power of the bright spots is time variable with peak power ranging from a few tens to a hundred of gigawatts. Moreover, we found that, for some perijoves, bright spots exhibit quasiperiodic behavior. The spots, within PJ4 and PJ16, each reappeared at almost the same system III position of their first appearance with periods of 28 and 22 minutes, respectively. This period is similar to that of quasiperiodic emissions previously identified in X-rays and various other observations. The bright spot position is in a specific region in the northern hemisphere in system III, but are scattered around the magnetic pole in the southern hemisphere, near the edge of the swirl region. Furthermore, our analysis shows that the bright spots can be seen at any local time, rather than being confined to the noon sector as previously thought based on biased observations. This suggests that the bright spots might not be firmly connected to the noon facing magnetospheric cusp processes.