A $1.6 billion that would study dark energy, hunt for Earth-like planets, and scrutinise stars and galaxies should be NASA's top space telescope priority in the coming decade, an expert panel says.
The recommendation comes from the US National Research Council. Every ten years, US science agencies task the organisation with canvassing the astronomical community and identifying the top research priorities. The final report of this decadal survey is the distillation of two years of work, 17 town hall meetings, and 324 papers submitted on future science opportunities.
The space mission that ranked highest is a telescope called Wide Field Infrared Survey Telescope (WFIRST), a 1.5-metre probe that would launch in 2020 and orbit a stable gravitational point about 1.5 million kilometres from Earth.
Like the James Webb Space Telescope (JWST), which will be sent to the same spot in 2014, WFIRST would be sensitive to infrared light. But the telescope would have a wider field of view, allowing it to take in large patches of the sky.
It would study dark energy, which seems to make up more than 70 per cent of the combined matter and energy of the universe and is causing the expansion of space to speed up; survey the galaxy's exoplanets; and work as a general-purpose instrument to investigate topics such as the structure of the Milky Way. "It's one set of hardware that can do three sets of observing jobs," says Marcia Rieke of the University of Arizona in Tucson, one of the committee's vice-chairs.
Wendy Freedman of the Observatories of the Carnegie Institution in Pasadena, California, who was not on the panel, agrees. "I think that the WFIRST mission is an imaginative solution to addressing both dark energy and exoplanets in one shot."
WFIRST would use three different techniques to study dark energy, all of which would measure how rapidly the universe grew in size over billions of years. During its baseline, 5-year mission lifetime, the telescope would find about 2000 distant stellar explosions to see how much their light has been stretched by the expansion of space. WFIRST would also look for telltale ripples in the distribution of matter on the sky that were set in place soon after the big bang. Finally, the telescope would snap some 2 billion galaxies to study how their light is bent by intervening mass, since the distribution of matter on a large scale can shed light on the balance between the competing effects of gravity and dark energy.
Such gravitational lensing would also be used to hunt for planets in the star-studded central region of the Milky Way. Light from a background star would be gravitationally bent and magnified in a telltale way by a planet around a foreground star. The technique, which is sensitive to small planets, could allow astronomers to get a measure of how common Earth-sized planets are at a variety of distances from their host stars.
WFIRST is based on the design for a NASA/US Department of Energy project called the Joint Dark Energy Mission. First conceived in 2003, the mission was set to start in 2009 but has been held up by unrealistic cost estimates and tight budgets.
Identifying the astronomical community's top priorities is only a first step. For the priorities to become realities, the recommendations would need to be implemented by the US science agencies that requested the report. Committee members will probably also brief members of Congress, who control the purse strings of agencies such as NASA.
Funding is likely to be a continuing source of uncertainty for astronomy missions in the coming decade. Unlike the previous decadal survey, the new study relied on an independent organisation to estimate the budget of potential missions. That could prevent the ballooning budgets that have plagued other missions, such as NASA's $5 billion JWST, whose soaring costs may make it difficult to implement new missions in the short term, Spaceflight Now reported on Thursday.
"The committee faced a very tight budget environment, and there is a lot of competition for resources," says Freedman. "I believe this report provides a clear roadmap forward."
While the committee's recommendations are designed to fit within NASA's projected budget, the agency must still determine how it wants to proceed. "We're not sure what will fit into the [astrophysics] programme yet," says NASA spokesman J. D. Harrington.
The committee's other recommendations for space missions include a boost in funding to a NASA programme that funds smaller missions, like the WISE infrared telescope currently in orbit (see Report slams NASA's neglect of small missions). It also gives high priority to the Laser Interferometer Space Antenna, a three-spacecraft gravitational wave detector that is also being considered by the European Space Agency (ESA). The committee also recommends support for technology to develop a high-resolution X-ray telescope called the International X-ray Observatory, which would be built with ESA and Japan's space agency, JAXA.
If you would like