The Galileo spacecraft gave us so much information about Europa that we’re planning to return soon.
Although Galileo was the first spacecraft to closely observe Europa, it wasn’t the first look we’ve had of the moon. Pioneer 10 captured images, albeit fuzzy ones, from about 321,000 kilometres (200,000 miles) away in 1973. These showed some of Europa’s albedo features, but that’s about it. The two Voyager probes gave us better images of the moon in the late-Seventies, showing enough detail to make some believe that there was a liquid ocean under its icy surface. Astronomers on Earth had been observing Europa since its discovery, and the Hubble Space Telescope provided some crucial details about its atmosphere in 1995. That same year, the Galileo spacecraft entered Jupiter’s orbit. After finishing its main mission in 1997, it went on an extended mission called Galileo Europa and made numerous flybys, coming within 587 kilometres (365 miles) of the moon. It gave us the most detailed images of Europa’s surface to date, as well as revealing its atmospheric composition, magnetic field and further potential for a subsurface ocean. Galileo finished in 2003 with the Millennium Mission, during which it collected further data on Ganymede and Io. In 2007, New Horizons imaged Europa on its way to Pluto.
Europa’s ocean and its potential for life have made it a target for future space exploration. There have been several proposed missions that haven’t made it past the early stages. NASA commissioned a study in 2012 to explore lower cost options for missions to Europa. The European Space Agency has a planned three-year mission titled JUICE (Jupiter Icy Moon Explorer) to check out Jupiter as well as Callisto, Ganymede and Europa. JUICE is currently scheduled for launch in 2022.