Here, we provide an overview of the phenomenon called the H Ly-α bulge at Jupiter, which manifests itself as a brightening in hydrogen emissions at low latitudes at around 100° longitude. We present observations of H Ly-α and molecular hydrogen emissions on the body of Jupiter obtained during the Cassini flyby in late 2000 and early 2001. The H Ly-α emission is highly organised by System III longitude and latitude, peaking at a brightness of 22 kR between 90 and 120° longitude, confirming the presence of the bulge. These observations add to a number of previous studies, showing that the feature is very long- lived, present over several decades. We show that there is a strong correlation between the prevailing solar H Ly-α flux (measured at Earth) and the peak brightness of the H Ly-α bulge at Jupiter, which supports the idea that it is primarily driven by solar resonance scatter. However, the primary source of this emission feature remains unknown, and we discuss a number of potential solutions.
Henrik Melin & Tom Stallard (University of Leicester)
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