"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, Caltech professor and lead author of one of two new research papers.
"Io’s sodium becomes very faint within 15 minutes of entering Jupiter’s shadow, but it takes several hours to recover after it emerges into sunlight," explains Carl Schmidt, astronomy professor at Boston University and lead author of the second paper. "These new characteristics are really insightful for understanding Io’s atmospheric chemistry. It’s neat that eclipses by Jupiter offer a natural experiment to learn how sunlight affects its atmosphere."