Observability of Callisto's Inductive Signature During the JUpiter ICy Moons Explorer Mission

• Published in: Journal of geophysical research. Space physics 2018-11, Vol.123 (11), p.9045-9054
• Main Authors: Liuzzo, Lucas, Simon, Sven, Feyerabend, Moritz
• Format: Article
• Language: English
• Subjects: Alfvén wings; Callisto; Current sheets; Electric currents; Flyby missions; Icy satellites; Ionosphere; JUICE mission; Jupiter; Jupiter magnetic field; Jupiter probes; Jupiter satellites; Jupiter's icy moons; Magnetic fields; Magnetic induction; Magnetic signatures; Magnetometers; Moon; moon‐magnetosphere interactions; Ocean currents; Oceans; Perturbation; Planetary magnetic fields; Planetary magnetospheres; Plasma currents; Plasma interactions; subsurface oceans
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2018JA025951

Using hybrid simulations and analytical calculations, we investigate the observable magnetic perturbations during the 12 planned Callisto flybys of the JUpiter ICy moons Explorer mission. During four of these encounters, Callisto will be embedded within Jupiter's magnetospheric current sheet. In these cases, Callisto's Alfvén wings and ramside magnetic field pileup will partially obscure any magnetic signatures associated with induction in a conducting layer at the moon, thereby severely complicating attempts to further constrain properties of a possible subsurface ocean. During one of these flybys, the plasma interaction will even generate magnetic signatures that are qualitatively similar to an induced field from the moon's interior. In this case, highly accurate measurements of the upstream flow parameters and Callisto's ionosphere are required to disentangle the induction signal from plasma effects. For the remaining eight encounters, Callisto's plasma interaction is expected to be sufficiently weak for an unobstructed observation of the moon's inductive signature. Plain Language Summary Jupiter's moon Callisto may possess a salty water ocean beneath its icy surface. Due to time variations of Jupiter's magnetic field near Callisto's orbit, electric currents would be induced in such an ocean, generating magnetic field perturbations detectable outside of the moon. Therefore, magnetometer observations near Callisto can be used to prove the existence and constrain the properties of such a subsurface ocean. However, Callisto is also embedded within Jupiter's magnetosphere and is continuously exposed to a flow of plasma particles that rotate synchronously with the planet. The deflection of this plasma around Callisto generates additional electric currents and associated magnetic perturbations that may obscure the induced field from Callisto's interior. Based on modeling of these plasma currents, we demonstrate that during several flybys of the upcoming JUpiter ICy moons Explorer mission, Callisto's induction signal will be buried by plasma effects beyond recognition. These plasma signatures may even look similar to induced fields and may therefore lead to a false positive identification of the ocean. Our work constrains flyby geometries that are suitable to detect water reservoirs beneath the surfaces of Jupiter's icy moons and is highly relevant for the successful planning of synergistic measurements during the JUpiter ICy moons Explorer mission. Key Points