The US space agency NASA and the European Space Agency (ESA) would conduct missions to Jupiter, Saturn and many moons that circle the planets, the agencies announced.
The missions include sending multiple spacecraft to the Jupiter and Saturn systems to explore the planets and their unique satellites, such as Jupiter's ice-covered Europa and Saturn's shrouded moon Titan.
The first mission to fly would be aimed at Jupiter. Dubbed the Europa Jupiter System Mission, it would send two orbiting spacecraft to study the planet and its large moons Io, Europa, Ganymede and Callisto in unprecedented detail, NASA officials said on Wednesday.
NASA would build one orbiter, the Jupiter Europa, while ESA would provide the other, Jupiter Ganymede. The spacecraft would launch in 2020 from different spaceports with the goal of reaching Jupiter by 2026 and spending three years studying the planet and its moons, NASA said.
"The decision means a win-win situation for all parties involved," said Ed Weiler, NASA's associate administrator for science missions at the agency's headquarters in Washington.
"Although the Jupiter system mission has been chosen to proceed to an earlier flight opportunity, a Saturn system mission clearly remains a high priority for the science community."
Like the proposed Jupiter mission, the Saturn expedition would consist of both NASA and European spacecraft.
Dubbed the Titan Saturn System mission, the flagship flight would include a NASA-built orbiter to study Saturn and its moons, as well as European lander and research balloon to continue the exploration of the planet's cloud-covered moon Titan. Saturn's moon
Enceladus, which harbours ice-spewing geysers, is also a major target for that mission.
Several technical hurdles must be overcome before the Saturn expedition can launch, and will require more study and technology development before the mission can move forward, NASA said.
Meanwhile, the Cassini orbiter managed by NASA, ESA and the Italian Space Agency is currently in orbit around Saturn, where it has been studying the planet and its many moons since it arrived in June 2004. The orbiter's European-built Huygens lander successfully touched down on Titan's surface in January 2005.
Mission managers are pushing to extend Cassini's flight by seven years to 2017.