Post-eclipse brightening of io confirmed

For about 15 minutes after Jupiter's satellite Io emerges from the planet's shadow after an eclipse, it unaccountably brightens far beyond its normal level. Observing Io with a spectrophotometer in 1978, F.C. Witteborn et al measured a brightness increase in the 4.7-5.4 micron range that was three to five times the brightness at other phase angles. Long a controversial phenomenon, this confirmation of Io's post-eclipse brightening has led to a search for possible explanations. Witteborn et al suggest that the transient flare-up is a complex thermoluminescent effect excited by interaction with Jupiter's magnetosphere, followed by solar heating as Io emerges from the shadow.

(Witteborn, F.C. et al; "Io: An Intense Brightening near 5 Micrometers," Science, 203:643, 1979.)

Comment. Io also modulates Jupiter's microwave emissions.