Energetic neutral atoms from a trans-Europa gas torus at Jupiter

The space environments--or magnetospheres--of magnetized planets emit copious quantities of energetic neutral atoms (ENAs) at energies between tens of electron volts to hundreds of kiloelectron volts (keV). These energetic atoms result from charge exchange between magnetically trapped energetic ions and cold neutral atoms, and they carry significant amounts of energy and mass from the magnetospheres. Imaging their distribution allows us to investigate the structure of planetary magnetospheres. Here we report the analysis of 50-80 keV ENA images of Jupiter's magnetosphere, where two distinct emission regions dominate: the upper atmosphere of Jupiter itself, and a torus of emission residing just outside the orbit of Jupiter's satellite Europa. The trans-Europa component shows that, unexpectedly, Europa generates a gas cloud comparable in gas content to that associated with the volcanic moon Io. The quantity of gas found indicates that Europa has a much greater impact than hitherto believed on the structure of, and the energy flow within, Jupiter's magnetosphere.     

Transient aurora on Jupiter from injections of magnetospheric electrons

Energetic electrons and ions that are trapped in Earth's magnetosphere can suddenly be accelerated towards the planet. Some dynamic features of Earth's aurora (the northern and southern lights) are created by the fraction of these injected particles that travels along magnetic field lines and hits the upper atmosphere. Jupiter's aurora appears similar to Earth's in some respects; both appear as large ovals circling the poles and both show transient events. But the magnetospheres of Jupiter and Earth are so different---particularly in the way they are powered---that it is not known whether the magnetospheric drivers of Earth's aurora also cause them on Jupiter. Here we show a direct relationship between Earth-like injections of electrons in Jupiter's magnetosphere and a transient auroral feature in Jupiter's polar region. This relationship is remarkably similar to what happens at Earth, and therefore suggests that despite the large differences between planetary magnetospheres, some processes that generate aurorae are the same throughout the Solar System.