NASA and ESA have jointly announced their plan to send the next big joint planetary exploration mission to Europa and Ganymede, two of the four planet-sized moons of Jupiter. The decision follows years of anticipation in the planetary science community, where the last such big decision was made back in 1988 when NASA and ESA agreed to work together on the Cassini-Huygens mission to Saturn and Titan. That completed its primary mission phase in 2008 and is now in the extended mission, still in orbit around Saturn.
The decision this time came down to a choice between two mission concepts. The plan that was not picked was another mission to the Saturn-Titan system, which capitalized on the momentum gained through the huge and continuing success achieved by Cassini-Huygens. The anticipation among planetary scientists was evident at formal meetings and in coffee rooms, where it has been a major topic of conversation for months. Even Nature weighed in last month and ran a two-page special report and an editorial on the subject, giving their push to the Saturn-Titan mission, arguing that the technological breakthroughs planned for the mission, including a hot-air balloon to float in the sky of Titan, will further open up frontiers of space exploration.
The final pick by NASA and ESA, called the Europa Jupiter System Mission (EJSM), involves two spacecrafts launched separately by NASA and ESA. The plan calls for sending NASA’s orbiter to Europa, and ESA’s to Ganymede. The probes are, for now, called Jupiter Europa Orbiter (JEO) and Jupiter Ganymede Orbiter (JGO). The decision was based on, among many factors, the maturity of the mission idea. NASA has been studying mission concepts for Europa since the late 1990s, the first of which was the Europa Orbiter, developed under the Faster, Better, Cheaper strategy but subsequently canceled after a series of FBC-mission failures.