Today, the National Academies of Science have released the results of its Decadal Survey, entitled "New Worlds, New Horizons in Astronomy and Astrophysics." As the name implies, the survey happens every 10 years, and is intended to obtain input from the astronomy community regarding what science projects should be made funding priorities by the US government. The report places priorities on three main objectives—exoplanets, the formation of the first structures in the Universe, and the physics that have governed its evolution—and produced a list of missions that places a high priority on observatories that can help solve problems in more than one of these areas.

Generally, NASA and the National Science Foundation are the main participants in this survey, but Stanford's Roger Blandford, who chaired the committee that prepared the report, mentioned that the Department of Energy took part for the first time. The committee was divided into five panels (planetary systems and star formation, stars and stellar evolution, galactic neighborhood, galaxies across cosmic time, and cosmology and fundamental physics), which were asked to formulate a single key question, and four areas of science that address it.

The committee received input via 17 town halls held around the nation, and over 300 papers were submitted for its consideration. In the end, they chose to prioritize the three areas mentioned above. The cosmic dawn category focuses on the formation of the earliest objects in the universe, from the first stars and black holes they produced to the earliest galaxies. This era has been poorly studied so far, as it occurs after the microwave background, but is heavily redshifted by its extreme age.

This may partly overlap with the physics of the Universe priority, which will focus on studies of inflation, dark matter, and dark energy, areas where astronomy can help inform our general understanding of physics. The last priority, new worlds, is a direct product of the fact that we've gone from a handful of exoplanets during the last decadal survey to hundreds, with hundreds of Kepler candidates waiting in the wings.

As Blandford stated at the press conference that accompanied the report's release, these priorities were balanced against some severe budget constraints—the survey assumed that the agencies involved would have flat budgets for the indefinite future. As such, the priorities were to maximize returns per dollar and limit the risk involved in the technology. This ended up placing a priority on ground-based observatories and projects that were already on the drawing board, since many of these have a mature technological foundation.

That said, major new space-based observatories were hardly ignored. What follows is a rough outline of some of the missions that the survey endorses.

Large space missions

Wide Field Infrared Survey Explorer (W-First) This will contribute both to the search for exoplanets, since it can image the dusty disk around stars, and to improving our understanding of dark energy by imaging extremely distant objects. It's considered medium to low risk, and can be operated for about $1.6 billion over its lifespan.

International X-ray Observatory (IXO) On the other side of the light spectrum, this is a proposal to combine NASA and ESA proposals to produce a successor to the Chandra X-ray Observatory. It will be a general purpose scope, able to generate X-ray spectra of everything from the accretion disk of a black hole to the hot gasses between galaxies. The survey calls on the US to fund half of its $5 billion price tag.

Laser Interferometer Space Antenna (LISA) This would put three craft millions of kilometers apart in an Earth-trailing orbit, and use interferometry to detect the presence of gravity waves. In contrast to Earth-based equivalents like LIGO, LISA would be sensitive enough to pick up things like white dwarf binaries. This would also require ESA support, and the successful completion of a pathfinder mission.

More Explorer missions The committee thinks that these low-cost, higher-risk missions give great returns for their costs, and so wants to see the budget for them slightly more than doubled.

Medium space missions

Here, the report focuses on technology development in two areas. One is to develop and validate technology for getting high-precision measurements of the polarization of the microwave background, focusing on ground-based observations before preparing the hardware for space. The second item is to use the information that's coming in about exoplanets to design hardware to provide direct observations of their properties.

Large ground projects

Large Synoptic Survey Telescope (LSST) This is an 8.4m scope planned for Chile that will scan the entire sky every three days, eventually building an archive of images over 100PB (petabytes) large. It should shed light on what the report calls the "time variable Universe," including everything from gravitational lensing events to small near-Earth objects. It's ready to build now, and will cost $460 million to construct and $40 million a year to run.

Mid-scale Innovations The committee received a lot of compelling proposals for projects with price tags in the $5 million-135 million price range, and recommends the NSF expand its existing budget for efforts on this scale.

Giant Segmented Mirror Telescope (GSMT) Giant is in the area of 30m with adaptive optics in this case. Globally, three of them are in progress with private funds. The report recommends that the NSF pick one, and pay a third of its costs to ensure that the researchers it funds have time on hardware of this class.

Atmospheric Čerenkov Telescope Array Both the US and European consortiums are looking to build hardware that will track the arrival of gamma rays with energies in the TeraElectronVolt. The US is advised to fund one, as risk and construction and operations costs are relatively low.

Medium ground projects

Cerro Chajnantor Atacama Telescope A 25m telescope for sub-millimeter wavelengths, CCAT will complement an existing instrument (ALMA) by performing surveys to identify objects for follow-up observations.

Although the decadal surveys are highly influential, Congress and NASA administrators will ultimately make many of the final decisions on funding priorities, and the global economic situation may make an era of flat budgets overly optimistic well before the decade is out. There are also some significant missions, like Juno, the Mars Science Laboratory, and the James Webb Space Telescope, that are already well-advanced, and due to be launched within the decade in question.

Listing image by NASA/JPL/SSI