2024-08-04 06:00:08
Jupiter has the brightest auroras in the solar system. One of the peculiarities of this planet, which it shares with Saturn, is also to have auroral emissions caused by three of its largest moons: Io, Europa, and Ganymede.
© The Watchers – M. Flouriot
These distinct emissions called “auroral fingerprints” are visible locally in several wavelength domains. These are created by charged particles, mainly electrons, which propagate along the magnetic field lines connecting the moons to Jupiter. By precipitating in the atmosphere of the giant planet, these electrons induce characteristic auroras, studied since the 2000s thanks in particular to observations of Hubble Space Telescope in the field ultraviolet. Since July 2016, the Juno probe has been flying over Jupiter’s poles at an altitude of only a few thousand kilometers, allowing for a detailed characterization of the structure of the moons’ auroral imprints. The combined analysis of data obtained on board Juno by the UVS spectrograph and the spectrometer JADE for which IRAP contributed to the optical system electrostaticallows us to probe both the properties of these emissions and also those of the charged particles which induce them.
By focusing their study on the auroral imprint of Ganymede, the largest moon in the solar system and the only one generating its own magnetic field, a team including scientists from CNRS Terre & Univers, in close collaboration with the Juno mission teams (SwRI, Princeton University), has, among other things, highlighted the influence of Ganymede’s mini-magnetosphere on its auroral imprint.
They thus confirmed that the size of the flux tubes, these tubular-shaped magnetic field lines connecting the moons to Jupiter’s atmosphere and in which electromagnetic waves and charged particles propagate, is significantly larger than those reported for Io and Europa by previous studies.
Juno’s observations of the auroral imprint thus provide a new method for studying Ganymede’s mini-magnetosphere, which will be explored in situ in an unprecedented way by ESA’s JUICE mission currently en route to Jupiter.
Juno (orbit in white at left) crosses a flux tube of the moon Ganymede. At Jupiter’s south pole, the auroral imprints of all three moons are observed simultaneously in ultraviolet by the Juno/UVS instrument and shown here in false color. These consist of two bright spots appearing white, followed by a diffuse emission called the auroral tail.
© CDPP-Inetum / NASA / SwRI / Juno-UVS / ESA / STScI / Jonas Rabia / Vincent Hue
References:
Rabia, J., Hue, V., André, N., Nénon, Q., Szalay, JR, Allegrini, F., et al. (2024).
Properties of electrons accelerated by the Ganymede-magnetosphere interaction: Survey of Juno high-latitude observations.
Journal of Geophysical Research: Space Physics, 129, e2024JA032604.
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