Dark energy and exoplanets prioritized by decadal survey.

The proposed Large Synoptic Survey Telescope (LSST) was the number one choice for a new ground based astronomical facility in the 2010 decadal survey.Todd Mason, Mason Productions Inc. / LSST Corporation

In a report that marries cosmic curiosity with down-to-Earth pragmatism, an expert committee has delivered its game plan for the future of US astronomy.

The much-anticipated 'decadal survey', kept tightly under wraps until its release today, recommends which astronomy and astrophysics projects NASA, the National Science Foundation (NSF) and the Department of Energy (DOE) should fund over the next ten years (see 'Programmes recommended by the survey'). It also reflects how the landscape of astronomy has changed in the past decade, by placing heavy emphasis on dark energy, a mysterious phenomenon responsible for accelerating the expansion of the Universe, and extrasolar planets — two fields that barely existed at the time of the previous survey, in 2001.

"What we've seen over the last decade and can confidently expect for the next is unscripted discovery," says astronomer Roger Blandford of Stanford University in California, chair of the 23-person committee charged with writing the report for the National Academy of Sciences.

But although the scientific questions raised in the report are no surprise — what is dark energy, and how common are Earth-like worlds? — its strategy for answering them is likely to raise eyebrows. Constrained by a fiscal climate that is drastically different from the one their predecessors faced ten years ago, committee members have avoided recommending specialized projects to tackle astronomy's two biggest questions. Instead, they have given highest priority to a new space telescope that can go some way towards addressing both.

WFIRST, or the Wide Field Infrared Survey Telescope, is a proposed 1.5-metre imaging telescope that would map the sky in the near infrared — a wavelength range also accessible with the James Webb Space Telescope (JWST), scheduled for launch in 2014. The difference is that, whereas the JWST is designed to gaze deeper into the Universe than ever before, WFIRST would look more widely, acquiring a massive data set that spans the sky. Such data would contain subtle clues — in the distance-brightness relationships of supernovae, the weak gravitational lensing, or the bending of light, by background galaxies and the three-dimensional clustering of matter in space — that can independently measure the influence of dark energy on the expansion of the Universe.