New Delhi: There are spectacular displays of polar lights on Jupiter, just like the Earth, caused by interactions with solar wind. However, some of the emissions are because of interactions with the Galilean moons of Io, Europa, Ganymede and Callisto, the four largest moons interacting with the extreme magnetic environment around Jupiter. These emissions are called auroral fingerprints, and are unlike any on Earth, with emissions in ultraviolet, visible, infrared and radio frequencies. Since the 2000s, scientists have studied the auroral fingerprints of Io, Ganymede and Europa, using the Hubble space telescope. The aurora fingerprint of Callisto, the outermost of the Galilean moons, has proven to be elusive, so far.
The auroral signatures of the Galilean moons marked by the first alphabets in their names. (Image Credit: Rabia, Hue, Louis, André, Nénon et al. Nature Commun. 16, 7791 (2025).).
Since July 2016, the Juno mission began observing the auroral regions using its ultraviolet imager. Now, a new study published in Nature Communications demonstrates for the first time that the ultraviolet auroral signature of Callisto can be teased out from the data collected by the most distant planetary orbiter, Juno. The observations revealed that the main auroral emissions were displaced from their usual positions in September 2019, resulting from a global expansion of the gas giant’s magnetosphere, resulting from a shifting in properties of the solar wind, revealing the auroral signature of Callisto that was otherwise masked by the intense auroral emissions in the region.
A comprehensive understanding of the Jovian system
By confirming the existence of the auroral signature of Callisto, the researchers have completed the scientific understanding of the moon-planet couplings in the Jovian system. The research indicates that the auroral signatures of all the four Galilean moons are generated by similar underlying physical mechanisms. The Juno spacecraft is one of the many extended NASA missions that is under threat by the proposed ‘Skinny Budget’ of the Trump-Vance administration.