  Jupiter's moon Io is the most volcanically active body in the Solar System
with hundreds of active volcanoes varying in intensity on different timescales.
Io has been observed during occultations by other Galilean moons and Jupiter
since the 1980s, using high-cadence near infrared photometry. These
observations encode a wealth of information about the volcanic features on its
surface. We built a generative model for the observed occultations using the
code starry which enables fast, analytic, and differentiable computation of
occultation light curves in emitted and reflected light. Our probabilistic
Bayesian model is able to recover known hotspots on the surface of Io using
only two light curves and without any assumptions on the locations, shapes or
the number of spots. The methods we have developed are also directly applicable
to the problem of mapping the surfaces of stars and exoplanets.
