SM057-07
Observations of Small Scale Structures in the Footprint of the Galilean Satellites by JIRAM
Observations of Small Scale Structures in the Footprint of the Galilean Satellites by JIRAM
Wednesday, 16 December 2020: 10:24
Virtual
Abstract:
The Jovian Infrared Auroral Mapper (JIRAM) on board Juno is a spactro-imager mainly designed to inspect
the atmosphere of Jupiter and its auroral emission. It includes two imagers in the L (3.3-3.6μm) and M bands
(4.5-5.0μm) and a spectrometer operating at 2-5 μm.
The orbit of Juno and the high resolution of the JIRAM imager allowed to acquire images of moon-related
aurorae in great detail. These images show a rich morphology including a main spot, a potential precursor,
a sequence of trailing spots and a fading tail. The phenomenon is due to the jovian magnetic field sweeping
past the Galiean moons, which generate Alfven waves travelling towards the ionosphere and set up field aligned
currents. When the associated electrons reach the ionosphere, they interact with the hydrogen and make it to
glow.
Here we focus on the small scale structure close to the main spot acquired using the L-band of the imager
from perijove 7 to perijove 26. This feature extends for aboout 4000 km and the typical distance between the
spots in the southern emisphere lies between 250 and 600km for both the Io and Ganymede footprints. This
distance decreases to 150km in the northern emisphere, which is the same scale length observed for the Euorpa
footprint in the South Pole. So far we found no correlation with orbital parameters such as the longitude of the
moons, which suggest us that such morphology is almost purely due to ionospheric processes.
A puzzling feature is the stillness of the secondary spots observed during PJ13 (Fig.1). The brightness of
the highlighted spots fades as time goes by, but their position remains the same, as can be noticed by contrast
with the moving main spot. This behaviour is consistently observed also during orbits 14, 16 and 26.
The characteristics of these spots are incompatible with multiple reflection of Alfven waves between the two
emispheres. Instead, we are currently investigating ionospheric processes like the feedback instability (FI) as a
possible candidate to explain the generation of the observed small scale structure. This process relies on local
enhacement of conductivity in the ionosphere, which is affected by electron precipitation. Besides, we are also
considering the interplay between the ionospheric resonator and the FI as a possible underlying mechanism.
the atmosphere of Jupiter and its auroral emission. It includes two imagers in the L (3.3-3.6μm) and M bands
(4.5-5.0μm) and a spectrometer operating at 2-5 μm.
The orbit of Juno and the high resolution of the JIRAM imager allowed to acquire images of moon-related
aurorae in great detail. These images show a rich morphology including a main spot, a potential precursor,
a sequence of trailing spots and a fading tail. The phenomenon is due to the jovian magnetic field sweeping
past the Galiean moons, which generate Alfven waves travelling towards the ionosphere and set up field aligned
currents. When the associated electrons reach the ionosphere, they interact with the hydrogen and make it to
glow.
Here we focus on the small scale structure close to the main spot acquired using the L-band of the imager
from perijove 7 to perijove 26. This feature extends for aboout 4000 km and the typical distance between the
spots in the southern emisphere lies between 250 and 600km for both the Io and Ganymede footprints. This
distance decreases to 150km in the northern emisphere, which is the same scale length observed for the Euorpa
footprint in the South Pole. So far we found no correlation with orbital parameters such as the longitude of the
moons, which suggest us that such morphology is almost purely due to ionospheric processes.
A puzzling feature is the stillness of the secondary spots observed during PJ13 (Fig.1). The brightness of
the highlighted spots fades as time goes by, but their position remains the same, as can be noticed by contrast
with the moving main spot. This behaviour is consistently observed also during orbits 14, 16 and 26.
The characteristics of these spots are incompatible with multiple reflection of Alfven waves between the two
emispheres. Instead, we are currently investigating ionospheric processes like the feedback instability (FI) as a
possible candidate to explain the generation of the observed small scale structure. This process relies on local
enhacement of conductivity in the ionosphere, which is affected by electron precipitation. Besides, we are also
considering the interplay between the ionospheric resonator and the FI as a possible underlying mechanism.