Washington

Sending a spacecraft to Pluto and the distant Kuiper Belt should be the United States' top priority in Solar System exploration, according to a 'decadal survey' of planetary science — the most thorough attempt yet to set a long-term agenda for research in the field.

NASA already is heeding the advice, released on 11 July by the National Academy of Sciences, and hopes to fund the on–off New Horizons mission (see Nature 414, 571; 200110.1038/414571b) to reach Pluto by 2020, according to Colleen Hartman, who heads the agency's Solar System exploration office.

The review is meant to build on the successful tradition of decadal reports for astronomy and astrophysics, which have been influential in guiding US government funding (see Nature 405, 381–382; 200010.1038/35013206).

The proposed agenda for 2003 to 2013 calls for three classes of planetary missions. Small (less than $325 million) missions would essentially continue NASA's existing Discovery programme, which has sent spacecraft to study asteroids and comets. The medium-sized (up to $650 million) category roughly matches the agency's New Frontiers line introduced this year, and would include the mission to Pluto and the Kuiper Belt, as well as a spacecraft to return samples from the Moon's south pole.

The most controversial recommendation is to revive the kind of large, expensive (more than $650 million) flagship missions that NASA abandoned in the 1990s. The panel, chaired by planetary scientist Michael Belton of Belton Space Exploration Initiatives in Tucson, Arizona, picked a spacecraft to explore Jupiter's moon Europa as the first entry in this category. Belton says that NASA's projected budget should allow for one such project every ten years or so. But Hartman says that the money isn't there.