Bruce Murray Space Image Library
Io's crescent
![Io's crescent](https://planetary.s3.amazonaws.com/web/assets/pictures/_266x266_crop_center-center_line/20130327_lor_0035208179_0x630_sci_1.png 266w)
The plume of the giant volcano Tvashtar is brightly backlit by the Sun. On the sunlit limb, there is a bright flash off of the smooth surface of the flat lava flows of Loki Patera; these flows look quite dark when seen with the Sun overhead, but in this lighting geometry the sunlight glances off the smooth surface as off a mirror, producing a flash of light.