Ganymede, Jupiter’s largest moon, is the only moon in our solar system with a magnetic field. The intrinsic magnetic field penetrates the surrounding space environment, creating a magnetosphere embedded in the magnetic field and sub-Alfvenian plasma current of Jupiter’s magnetosphere.

NASA’s Juno spacecraft made a brief flyby of Ganymede and flew through its magnetosphere on June 7, 2021, including an outgoing crossing of Ganymede’s upstream magnetopause. During this flyby, the spacecraft observed evidence of magnetic reconnection.

A team led by the Southwest Research Institute used Juno data to examine the electron and ion particles and magnetic fields as the magnetic field lines of Jupiter and Ganymede merged, snapped and reoriented due to heating and acceleration of the region’s charged particles.

Magnetic reconnection is a fundamental plasma physical process by which magnetic field lines can merge and reorient. In addition, this process transforms stored magnetic energy, which can heat and accelerate local ions and electrons.

Dr. Robert Ebert, lead author of a Geophysical Research Letters paper detailing the findings, said: “We interpreted the presence of accelerated electrons traveling along the magnetic field at Ganymede’s magnetopause as evidence that magnetic reconnection occurred there during the Juno flyby. These observations further support the idea that magnetic reconnection at Ganymede’s magnetopause may be a driver of dynamical processes in the local space environment around this moon of Jupiter.”

Aboard Juno, the SwRI-designed Jovian Auroral Distributions Experiment (JADE) saw increased electron fluxes, including accelerated, magnetic field-aligned electrons. It is believed that the reconnection Juno saw was related to the generation of Ganymede’s aurora.

Dr. Stephen Fuselier, a co-author of the article, said: “The accelerated electrons observed by JADE are similar to those observed by NASA’s Magnetospheric Multiscale (MSS) spacecraft during reconnection at Earth’s magnetopause. That’s one of the exciting results of the Ganymede flyby: despite the vast differences between Ganymede and the earth, we find similarities in the universal process of magnetic reconnection.”

Thomas Greathouse, a Juno scientist from SwRI, said: “Nothing is simple – or small – when you have the largest planet in the solar system as a neighbor. This was the first measurement of this complicated interaction at Ganymede. This gives us a very early tantalizing taste of the information we expect to learn from ESA’s JUICE mission.”

Magazine reference:

  1. RW Ebert et al. Evidence for magnetic reconnection at the upstream magnetopause of Ganymede during the PJ34 Juno Flyby. Geophysical Survey Letters. DOI. 10.1029/2022GL099775