This story was updated at 5:50 p.m. EST.
NASA and the European Space Agency (ESA) are pushing ahead with proposals to send ambitious new missions to explore Jupiter, Saturn and the many moons that circle both planets, the two space agencies announced Wednesday.
The proposed missions call for sending multiple spacecraft to the Jupiter and Saturn systems to explore the gas giant planets and their unique satellites, such as Jupiter?s ice-covered Europa and Saturn?s shrouded moon Titan.
?It?s just a remarkable effort that I see,? said Jim Green, director of NASA?s planetary science division, in a teleconference with reporters. ?The communities have really come together on both sides of the pond.?
NASA and ESA officials announced plans for the flagship mission proposals and a rough schedule for the first to fly - the Jupiter-bound expedition - on Wednesday after a meeting between the two space agencies in Washington, D.C., last week. NASA envisions launching its Jupiter and Saturn probes atop expendable Atlas 5 rockets, U.S. space agency officials 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, D.C. "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."
Return to Jupiter
Dubbed the Europa Jupiter System Mission, the Jupiter-bound expedition would send two orbiting spacecraft to study the planet and its large moons Io, Europa, Ganymede and Callisto in unprecedented detail, NASA officials said.
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 officials said.
NASA?s share in the mission could cost up to $3 billion, while Europe has set aside about 850 million euro (about $1 billion) for its next flagship mission. The European Jupiter probe is also known as Laplace at ESA. While neither mission is currently fully funded, NASA is setting aside about $10 million to continue studying design challenges for its Jupiter Europa orbiter, Green said.
NASA?s last dedicated mission to Jupiter was Galileo, which spent eight years studying the planet and its moons before intentionally plunging into the gas giant in 2003 to end its flight. The next probe slated to fly to the planet is NASA?s Juno, which is scheduled for an August 2011 launch.
?For the Jupiter Europa mission, the overarching goal is to investigate the emergence of potentially habitable worlds around gas giants,? said Curt Niebur, NASA?s program scientist for the outer planets. ?We?ll take a close look at Europa, to better define its habitability.?
Jupiter?s moon Europa is covered with a thick crust of ice that hides what astronomers believe to be a vast liquid ocean beneath its frozen exterior. In addition to studying Jupiter itself and flying by its other large satellites, NASA?s Jupiter Europa spacecraft would be able to orbit Europa and build global maps of the moon?s surface, topography and composition. A ground-penetrating radar and gravity-measuring sensors would also probe Europa?s interior to obtain definitive proof whether the underground ocean exists.
?We all firmly believe that there?s an ocean under the ice of Europa,? Niebur said. ?This mission is going to verify that using three different lines of inquiry.?
Europe?s Jovian probe would mirror NASA?s in-depth scrutiny of Europa at Ganymede, which is the largest of Jupiter?s moons, as well as the largest natural satellite in the solar system. The moon is larger than the planet Mercury. While NASA?s spacecraft will end its mission in orbit around Europa, Europe?s would do so circling Ganymede, NASA officials said.
Sailing to Saturn
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 harbors ice-spewing geysers, is also major target for that mission. ESA officials have referred to their mission to Saturn and Titan as Tandem.
The daunting technical hurdles involved in assembling the mission will require more study and technology development before the flight can go forward, NASA officials said. Those hurdles, which include trying to keep spacecraft trim enough to fit on their rockets, led NASA and ESA officials to propose flying the Jupiter mission first, they added.
?Titan will not be forgotten,? Green said.
Under NASA?s current plan, the Titan Saturn System mission would take about 10 1/2 years to reach Saturn if it launched in the 2020 timeframe. NASA?s orbiter would spend about two years circling Saturn to study the planet, Enceladus and other moons, and then spend about 1 1/2 years in orbit around Titan, Niebur said.
Niebur said Titan?s major draw is its chemistry, which appears to have many parallels to what the early Earth may have been like in the ancient past. Images and data from the Cassini orbiter have found evidence of liquid methane lakes and rain on the cloudy Saturnian moon.
?Titan is felt to be a very Earth-like world in terms of the processes going on,? Niebur 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.
"This joint endeavour is a wonderful new exploration challenge and will be a landmark of 21st century planetary science," said David Southwood, ESA?s director of science and robotic exploration. "What I am especially sure of is that the cooperation across the Atlantic that we have had so far and we see in the future, between America and Europe, NASA and ESA, and in our respective science communities is absolutely right. Let's get to work."
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