Astronomers using W. M. Keck Observatory on Maunakea in Hawaiʻi have discovered that aurorae at visible wavelengths appear on all 4 major moons of Jupiter: Io, Europa, Ganymede, and Callisto.
Using Keck Observatory's High-Resolution Echelle Spectrometer (HIRES) as well as high-resolution spectrographs at the Large Binocular Telescope and Apache Point Observatory, a team led by Caltech and Boston University observed the moons in Jupiter's shadow so that their faint aurorae, which are caused by the gas giant's strong magnetic field, could be spotted without competition from bright sunlight reflected off of their surfaces.
"These observations are tricky because in Jupiter's shadow the moons are nearly invisible. The light emitted by their faint aurorae is the only confirmation that we've even pointed the telescope at the right place," says Katherine de Kleer, assistant professor of planetary science and astronomy; Hufstedler Family Scholar; and lead author of one of two new research papers published today in the Planetary Science Journal describing the discovery.
