Sunny Priyan
This composite image reveals the Saturn Lyman-alpha bulge—an unexpected hydrogen emission excess observed by Voyager 1, Cassini, and Hubble between 1980 and 2017.
A 2017 Hubble near-ultraviolet image from Saturn’s northern summer serves as a reference for sketching the planet’s Lyman-alpha emission, with its rings appearing darker due to lower UV reflectivity.
Above Saturn’s rings and dark equator, the Lyman-alpha bulge appears as a 30° latitudinal band, shining 30% brighter than its surroundings, while the southern hemisphere shows dimmer emission.
North of the Lyman-alpha bulge, brightness gradually fades with latitude toward the bright aurora, where a dark spot marks the footprint of Saturn’s spin axis.
Icy ring particles raining onto Saturn’s atmosphere, combined with seasonal effects, are believed to cause heating that boosts hydrogen’s Lyman-alpha reflectivity in the bulge region.
The unexpected ring–atmosphere interaction is now being studied to develop diagnostic tools for detecting extended Saturn-like ring systems around distant exoplanets.