What is OPAL? OPAL (Outer Planet Atmospheres Legacy) is a project to obtain long time baseline observations of the outer planets in order to understand their atmospheric dynamics and evolution as gas giants. The yearly observations from OPAL throughout the remainder of Hubble’s operation will provide an important legacy of time-domain images for use by planetary scientists. Viewers might notice that some of the images of the same planets appear to be different colors. This is due to the fact that over the years, from Voyager to Hubble, many different instruments, and many different filters have been used.