Published online 18 February 2009 | Nature | doi:10.1038/news.2009.109

Corrected online:

News

Space agencies target Jupiter system for orbiters that will launch in 2020.

NASA and the European Space Agency (ESA) have chosen Jupiter's moons as the destination for their upcoming joint outer planet flagship mission. A trip to Saturn's moon Titan needs further study, the agencies decided.

The Europa Jupiter System Mission will launch two orbiters, one built by NASA and the other by the ESA, in 2020, with a scheduled arrival time in the Jupiter system of 2026. The NASA orbiter will study the icy shell of Jupiter's moon Europa, which may harbour an ocean capable of supporting life. The ESA orbiter will investigate Ganymede, the largest moon in the solar system, which has a unique magnetic field.

Europa, as imaged by the New Horizons spacecraft on its way to Pluto. NASA/JHUAPL/SwRI

"I'm thrilled", says Robert Pappalardo, a planetary scientist at the Jet Propulsion Laboratory in Pasadena, California, who has worked on Europa mission studies for more than a decade. "We've been working long and hard on this. It's the right place to go to understand the potential habitability of icy satellites."

Although the Europa mission was deemed more technically ready, NASA and the ESA did not close the door on a Titan mission. "Titan will not be forgotten", says Jim Green, director of the planetary science division at NASA headquarters in Washington DC. The Titan studies will provide "very important" input to an upcoming ranking of potential planetary missions, he says.

The Europa mission will help scientists investigate the emergence of habitable worlds around gas giants, says Curt Niebur, a programme scientist for outer planets research at NASA. A Titan mission would have sent a lander and a balloon to explore the moon's organic chemistry, which may be similar to that of the early Earth.

Jonathan Lunine, a planetary scientist at the University of Arizona in Tucson who supported the Titan mission, says the decision is not entirely surprising. The Europa mission was given top priority in a 2002 community survey of solar system exploration. "To imagine that it would turn the decadal survey process upside down was unrealistic", he says. Lunine says the real question is when the postponed Titan mission might occur, an issue left open by NASA. "I'd like to see Titan again before I die", he says.

The NASA portion of the Jupiter mission will cost at least $2.5 to $3 billion, says Green. The European portion of the mission, called Laplace, still needs to compete with two other missions to secure a slot within ESA's Cosmic Vision programme.

With reporting by Eric Hand.