For nearly a decade, officials at NASA and the European Space Agency (ESA) have discussed a shared mission to study dark energy. But any substantive collaboration on Europe's dark energy mission, Euclid, now appears to be dead.
Last month, ESA green-lighted Euclid as a medium-class mission to be launched in 2019. After the decision was announced, NASA officials met with their ESA counterparts to discuss how NASA could contribute to the project. Such a partnership was seen as advantageous for U.S. astronomy, especially in light of an impending budget squeeze that could delay NASA's own dark energy mission until 2025 or later. Although no formal agreement was reached, the two sides agreed that NASA would contribute a piece of hardware such as detectors or reaction wheels—which help turn a space observatory in a desired direction—and, in turn, gain a seat on Euclid's 12-member science team.
That contribution is likely to be $20 million or less, said Geoffrey Yoder, acting director of NASA's astrophysics division, at a 21 November telecom of a NASA advisory panel. The figure represents a little over 3% of the $600 million project cost.
Last year, the U.S. astronomy community's decadal survey report recommended that the United States take a "leading role" in any U.S.-Europe joint dark energy mission. Such a partnership was thought to mean a 50% contribution. But by the time the committee expressed its view, ESA officials had already developed detailed plans for Euclid's design, instrumentation, and science and was loathe to adjust them. NASA officials also weighed the merits of a 20% contribution.
The recent talks confirm that ESA officials have made up their minds to launch Euclid as an all-European mission, with negligible support from the United States.
A hardware contribution to Euclid, Yoder said, will give U.S. scientists access to about "10% of the whole science available" during the mission's limited access period, before the observed data are made public. He said ESA is weighing a similar hardware contribution to the Wide-Field Infrared Survey Telescope (WFIRST), NASA's own dark energy mission that is still in the conceptual stage. In return, Yoder said, ESA would like an opportunity to "drive some of the science on WFIRST."