Astronomers in the US have identified the highest priority research activities in astronomy and astrophysics for the coming decade. The decadal survey, released today by the National Research Council, says understanding the nature of dark energy, studying the formation of galaxies and black holes, and seeking nearby habitable planets are the most important science objectives for the next 10 years and beyond. Their decisions are influenced by the opportunity of international collaboration and for the first time the decadal survey also takes into account the project’s technical feasibility as well as its cost and current schedule

The survey, which included the input of over 200 scientists, prioritizes projects in four categories – large and mid-size space-based missions, as well as large and mid-size ground-based telescopes.

Two projects that will study dark energy – a mysterious substance that accounts for 74% of the total mass-energy of the universe and is causing its rate of expansion to increase – are given the highest priority in the large space-based and the large ground-based categories.

The search for alien worlds

The Wide-Field Infrared Survey Telescope (WFIRST), which has an estimated cost of $1.6bn and is scheduled for launch in 2020, is given top priority in the large space-based class. WFIRST will take measurements of supernova distances, gravitational lensing and measure baryon acoustic oscillations – clustering of matter due to acoustic waves that propagated in the early universe – to determine the effect of dark energy on the evolution of the universe.

The committee chose WFIRST, which is a collaboration between NASA and the US Department of Energy, as top priory as it offers a chance for international participation. It also presents a relatively low technical and cost risk making its completion "feasible within the decade, even in a constrained budgetary environment". The telescope is based on a design for the planned $650m Joint Dark Energy mission, which will now be amalgamated with a mission to search for exoplanets.

"WFIRST not only gets at all the dark energy [priorities], but it also has significant capability in exoplanet science and will do outstanding work in infrared survey science," Michael Turner, a cosmologist at the University of Chicago and the Kavli Institute for Cosmological Physics told physicsworld.com. Turner, who served on the 23-member committee for the decadal survey, also notes that the survey did not reject the idea of a possible collaboration with the European Space Agency (ESA) to combine its planned Euclid dark-energy mission with WFIRST.

Top priority for large ground-based missions is given to another telescope that will attempt to study the nature of dark energy and dark matter. The $465m Large Synoptic Survey Telescope (LSST), which when complete in 2015 will survey the entire sky every three nights with an 8.4 m optical telescope in Chile. The telescope came top in the ground-based category due to its "capacity to address so many of the science goals" of the decadal survey.

"This is extremely good news for the project, and a great relief," says astronomer Andrew Lawrence from the University of Edinburgh who was attending a meeting about the LSST in Arizona this week. "It does not guarantee that it will now get the rest of its funding, but it is a very good bet." Construction of LSST is due to begin in 2013, which will take around two years. After a year of testing, science operations are then set to begin in 2015.

Setting priorities

Studying gravitational waves and the nature of black holes make up the other priority missions in the large space-based category. After WFIRST, second priority is given to the "explorer programme", which supports small- and medium-scale missions such as the Wide-Field Infrared Survey Explorer that launched in December to probe the coolest stars in the universe and the structure of galaxies. These missions are launched within five-year time scales and the survey recommends that the budget for this programme is increased from $40m to $100m per year by 2015.

The Laser Interferometer Survey Telescope (LISA), a joint mission between NASA and the European Space Agency (ESA), is third priority for large space-based missions. To be launched in 2025 and costing roughly €2.4bn, LISA will consist of three identical spacecraft flying five million kilometres apart from each other in a triangular formation. Laser beams directed between each of the three pairs of spacecraft will measure minute changes in the distances between the craft caused by the passage of gravitational waves.

The fourth priority for large space-based missions is the $5bn International X-ray Observatory (IXO), which is planned for launch in 2021 and will study black holes and hot gas associated with galaxies and stars. The report says that there are still some cost and technical uncertainties concerning the IXO, which is reflected in the mission’s lower priority.

Astronomy from the ground

In the large ground-based category, the "mid-scale innovations programme" that will study new telescope and instrumentation designs and fund telescopes in the $4m to $135m range gets second priority after LSST with a recommended funding of $40m per year. While third priority is given to a large optical and near-infrared telescope – a Giant Segmented Mirror Telescope (GSMT) – to be built in the coming decade at a cost of around $1bn. Two telescopes – the Giant Magellan Telescope and the Thirty Metre Telescope – are currently being developed as a GSMT and the committee says that a choice between the two projects should be made "as soon as possible for a federal partnership at a level of about a 25% investment in one of them".

Fourth priority in the large ground-based projects is the $400m Advanced Gamma-ray Imaging System (AGIS), which will study high-energy gamma rays from black holes and seek indirect evidence for dark matter annihilation.

At a glance: Decadal survey priorities

Space based

Large-scale: (in priority order): WFIRST; Explorer programme; LISA; and IXO.

Medium-scale: The "new worlds technology development programme" to design a future mission to study nearby Earth-like planets; "inflation probe technology development programme" to prepare for a potential cosmic microwave-background mission to study the epoch of inflation; and the Space Infrared telescope for Cosmology and Astrophysics (SPICA).

Ground based

Large-scale (in priority order): LSST; Mid-scale Innovations Programme; GSMT; and AGIS.

Medium-scale: The Cerro Chajnantor Atacama Telescope – a millimetre/submillimetre telescope that will study galaxies, stars, and interstellar gas.