NASA and the European Space Agency are going forward with both outer planet exploration missions that were presented at a competitive review at ASU last month. Arizona scientists (including Jonathan Lunine at UA and Ron Greely at ASU) are key players in each mission.
The Europa Jupiter System Mission was found to be more technically feasible to launch first and it will be followed by the Titan Saturn System Mission.
The Europa Jupiter System Mission would use two robotic orbiters to conduct detailed studies of the giant gaseous planet Jupiter and its moons Io, Europa, Ganymede and Callisto. NASA would build one orbiter, initially named Jupiter Europa. ESA would build the other orbiter, initially named Jupiter Ganymede. The probes would launch in 2020 on two separate launch vehicles from different launch sites. The orbiters would reach the Jupiter system in 2026 and spend at least three years conducting research.
Europa has a surface of ice, and scientists theorize it has an ocean of water beneath that could provide a home for living things. Ganymede, the largest moon in the solar system, is the only moon known to have its own internally generated magnetic field and is suspected to have a deep undersurface water ocean.
The orbiters would spend nearly a year orbiting Europa and Ganymede. NASA's probe would investigate whether Europa might harbor life, and ESA's spacecraft would orbit Ganymede to conduct investigations of the surface and interior of this satellite, to better understand the formation and evolution of the Jovian system.
I worked on the Voyager project in 1979-80 and published some of the early interpretations of the tectonics of Ganymede, and it continues to fascinate me, so I'm personally excited about this decision.
The Titan Saturn System Mission would consist of a NASA orbiter and an ESA lander and research balloon.
[Parts of this post are taken from the NASA press release]