Scientific and technical teams from NASA and the European Space Agency are fleshing out ideas for the next mission to fly to an outer planet — either to Jupiter or Saturn. A decision on which of those two exploration targets will be the destination for the space agency's next multibillion-dollar flagship mission is expected by year's end. "We have the outer planet flagship mission in the (NASA) budget ... I do believe it will happen," said Fran Bagenal, a professor of astrophysical and planetary sciences at the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder. "I couldn't have said that four years ago ... now I have great confidence that this will happen." Bagenal is chair of the Outer Planets Assessment Group, which was established by NASA in late 2004 to identify scientific priorities and pathways for exploration in the outer solar system. In 2007, NASA completed a series of studies for flagship missions, honing down the list to the two candidate missions that now are under further study by both NASA and ESA. During a two-day OPAG meeting in late March, officials provided a status report on the two outer planet exploration concepts now on the table: a Europa-Jupiter System Mission and a Titan-Saturn System Mission.
Each of those mission scenarios has multiple components with both ESA and NASA contributing to whichever outer planet investigation is down-selected. The Europa-Jupiter mission involves two orbiters with instruments designed to operate in the severe radiation environment of Jupiter. In addition to ESA and NASA, Russia also has expressed interest in the mission, proposing a Europa lander.