Io may have a bright dawn terminator

A test of the thermoluminescence properties of Io is proposed which can be performed with the unique optical observations programmed for Voyager 1's close flyby of that Jovian satellite. It is suggested that if Io's surface is thermoluminescent with a characteristic post-eclipse-brightening time of the order of 10 min, there should be a characteristic bright rim on the sunlit side of the satellite's dawn terminator. It is noted that the spatial resolution of six-color pictures to be taken by Voyager 1 should be sufficiently adequate to reveal the bright dawn terminator if it exists and is bright enough. A mathematical model illustrating the bright-dawn-terminator effect is presented.