OPAL—the Outer Planet Atmospheres Legacy program—is a Hubble Space Telescope (HST) imaging program that maps the four giant planets every year. The program cements the long-term legacy of HST by ensuring a regular cadence of giant planet observations to fill temporal gaps between individual programs. The main goal of OPAL is to study long-term trends tied to seasonal or other evolutionary cycles (including storm activity, wind field variability, and changes in aerosols) in the highly dynamic atmospheres of the giant planets.
At almost 400 orbits by the end of 2024, OPAL is the largest and longest-running solar system program ever conducted with HST.