NEWS NATURE|Vol 437|1 September 2005 NASA/SPL By Jupiter: the frosty satellite Europa features frequently in mission wish lists.

Designs on Europa unfurl

Mission designers at NASA may have found a allowed to send their plutonium-powered examine Europa’s icy face at high resolution way to explore Jupiter’s moon Europa without spacecraft past Earth and Venus to pick up from orbit. busting the agency’s budget — by flying past propulsive energy before heading into the Scientists who have been lobbying for a Earth first. outer Solar System. NASA has come under fire Europa mission after the cancellation of the Europa has long been of interest to plane- from activist groups in the past for launching Jupiter Icy Moons Orbiter (see Nature433, tary scientists because of the ocean that is radioactive material into space. 342; 2005) hope the Europa Geophysical thought to lie beneath its icy crust, which may The addition of Venus and Earth ‘gravity Explorer will make it into NASA’s budget be a possible habitat for life. The National assists’ makes the trip to Jupiter longer, but request as early as next year. This would allow Academy of Sciences and other advisory allows a heavier spacecraft, with a substantial work to begin in 2007. groups have consistently listed Europa among scientific payload, to launch on a single rocket. That may be optimistic, given competing the top destinations for future space missions. The Delta IV rocket in the financial demands from the belea- But sending a spacecraft there is complicated study would still be an expen- “NASA has eased guered space shuttle, the Moon– by Europa’s harsh radiation and the large sive ride — any Europa mission a key restriction Mars astronaut programme and amount of rocket fuel needed to brake into is expected to cost upwards of other science projects that have orbit. An earlier mission design from NASA’s $1 billion. But the mission may that was born of run into money troubles. Jet Propulsion Laboratory (JPL) in California now fit within NASA’s target political concerns.” But the mission could get back- foundered in 2001 owing to cost and technical budget for the first time. ing from NASA administrator difficulty. And plans for a more ambitious The Europa Geophysical Explorer, as the Mike Griffin, who told a Senate committee in nuclear-powered mission, the Jupiter Icy concept is dubbed, could launch as early as May that “You may look forward, in the next Moons Orbiter, have also been scrapped — at 2012, carrying 150 kilograms of payload, year or maybe even sooner, to a proposal for a least for the foreseeable future. including an ice-penetrating radar, a suite of Europa mission as part of our science line.” But a study completed by JPL this summer remote sensing instruments and perhaps a And international participation could help. has broken some of the previous barriers to small lander. The spacecraft would take more Expectations are still high that any Europa visiting Europa. Work on the suspended than six years to reach Jupiter and then spend mission will be done jointly with the Euro- nuclear mission led to progress in building a year-and-a-half orbiting the planet, includ- pean Space Agency (see Nature434,551; radiation-resistant spacecraft components. ing close fly-bys of Europa, Callisto and 2005). This is especially so after the successful And in setting ground rules for JPL’s study, Ganymede, before ending with a 30-day inten- cooperation on the Cassini–Huygens mission NASA eased a key restriction that was born of sive exploration of Europa. That would be long to Saturn. ■ political concerns: mission designers were enough to map the subsurface ocean and Tony Reichhardt

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