Published online 5 September 2007 | Nature | doi:10.1038/news070903-13
Corrected online: 10 September 2007

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Dark energy probe gets high praise

Independent panel prioritizes NASA programmes.

The Joint Dark Energy Mission could be flying by 2014.The Joint Dark Energy Mission could be flying by 2014.LBL

An independent panel asked to review a major set of NASA missions has given the thumbs up to a satellite designed to probe dark energy. Less lucky was a major X-ray observatory, which the panel recommends be deferred for now.

The report, by the US National Research Council (NRC), prioritizes the items of the Beyond Einstein programme, which was set up in 2002 to determine ways of studying exotic forms of matter and energy. The original programme list included five missions (see 'Waiting list'), which were meant to be spread out over the subsequent 25 years.

But a budget crunch at NASA, together with President George W. Bush's ambitious and costly plan to return astronauts to the Moon, has forced the delay of the Beyond Einstein programme. Last year, the US Congress asked the independent NRC to rank the projects on the basis of scientific importance and feasibility.

The panel's final ranking, released today, differs from that in previous NASA and NRC prioritizations. NASA is now determining how best to use the advice.

Top marks

The panel gives top marks to a Joint Dark Energy Mission (JDEM) to probe dark energy, a mysterious force that is pushing the Universe apart. "JDEM will significantly advance both dark energy and general astrophysical research," the report reads. In addition, the panel says, its billion-dollar price tag, to be split roughly equally with the US Department of Energy, makes it one of the cheaper options. The panel recommends starting the JDEM mission, for which the technologies are largely established, as early as 2009.

"That's great news," says Saul Perlmutter, an astrophysicist at the Lawrence Berkeley National Laboratory in California, who leads one of the JDEM concept design teams. Perlmutter says that the panel's findings may allow a dark energy mission to fly as early as 2014.

The panel also gives a high priority to the Laser Interferometer Space Antenna (LISA), a set of three spacecraft with a pricetag of US$2.3 billion. LISA would be used to probe gravity waves — ripples in the fabric of space time created by massive objects such as black holes and neutron stars. "LISA promises to open a completely new window into the heart of the most energetic processes in the universe," the report says.

However, it adds, the project should remain in the development phase until a European mission to test several critical components of the system returns its results. That is currently scheduled for late 2009 or early 2010, according to Oliver Jennrich, the LISA project scientist for the European Space Agency who is located in the Netherlands.

Tied for last

The result is that the remaining missions — a probe to study the inflation of the Universe, a black hole finder, and a giant X-ray telescope — are likely to be deferred, perhaps indefinitely. It suggests continuing research and development funding until the next astronomy decadal review, which will begin as soon as later this year.

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The finding is an especially bitter pill for X-ray astronomers, whose $2.1 billion Constellation-X telescope was given a high priority in the last decadal survey. "It's disappointing," says Harvey Tananbaum, director of the Chandra X-Ray Observatory Centre at Harvard University in Cambridge, Massachusetts. "Constellation-X makes a huge step forward in terms of X-ray spectroscopy," he says. He adds that he believes the programme will win a high-priority in the next decadal review.

"We are grateful to [the committee] for the hard work they've done," NASA spokesperson Grey Hautaluoma said in an e-mail. NASA declined to comment further about how they would treat the report at the time Nature went to press.

Additional reporting by Ewen Callaway.

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Corrected:

This article originally stated that the panel concluded three projects “must be deferred indefinitely”. This has been corrected to better reflect the wording of their report.