Time series of Io's total 3.8 μm endogenic brightness values for both eclipse and sunlit observations (where the estimated contribution from reflected sunlight has been subtracted). The outburst events are the points above 150 GW sr⁻¹ μm⁻¹. Despite the larger uncertainty in the sunlit observations, the events in 2018 May and 2021 August stand out. The gray shaded regions show the periods of Jupiter's solar conjunction when Io is not visible from Earth.