Juno Witnesses Extreme Compression of Jupiter's Magnetosphere

Abstract In October 2024, the Juno spacecraft observed an extreme compression of Jupiter's magnetosphere. This event pushed the magnetosheath into an unprecedented distance of only 30 Jupiter radii from Jupiter. This suggests an enhanced Solar Wind (SW) dynamic pressure (DynP), that was likely produced from a coronal mass ejection after an X1.8 class solar flare. The compression brought the magnetosheath, observed at a high southern latitude, to the closest distance ever observed from Jupiter. Using data from multiple instruments on Juno to identify magnetosheath signatures, it is shown that Juno had many encounters with the magnetosheath as it moved inward from apojove to perijove. This included many short‐lived encounters that were not readily identifiable from a single data set. From model estimates, a SW DynP of around 1.2 is suggested for this event, consistent with previous upper estimates observed in the vicinity of Jupiter's orbital path. Remote imaging suggests the magnetosphere remained compressed for several days after this event. The event raises the possibility that Jupiter's magnetosphere on the dayside could potentially shrink inside of Callisto's orbital path, and that if Callisto happened to be on the dayside of Jupiter at the time (although it was on the nightside during this event), it could find itself outside of the jovian magnetosphere and exposed directly to the SW.