Various researchers have proposed that the atmosphere of Io freezes onto the surface when it passes into the shadow of Jupiter. Evidence for this is a "post-eclipse brightening", where the moon sometimes appears a bit brighter as if covered with frost immediately after eclipse. After about 15 minutes the brightness returns to normal, presumably because the frost has disappeared through sublimation. Besides being seen through ground-based telescopes, post-eclipse brightening was found in near-infrared wavelengths using an instrument aboard the "Cassini" spacecraft. Further support for this idea came in 2013 when the Gemini Observatory was used to directly measure the collapse of Io's atmosphere during, and its reformation after, eclipse with Jupiter.