A composition of images captured by the Hubble Space Telescope brings together the solar system’s giant planets on a grand tour of the outer planets. Jupiter, Saturn, Uranus, and Neptune are among the targets of periodic observations in programs such as OPAL (Outer Planets Atmospheres Legacy) to keep an eye on the changes that occur over time in their atmospheres. Along with other instruments, which in some cases include space probes, Hubble is an important contributor to studies of gas planets. Programs such as OPAL are also useful in developing models for studying gas exoplanets in other star systems.