What Is Dark Energy? 'Beyond Einstein' Program Aims To Investigate

Beyond Einstein is NASA's research roadmap for five proposed mission areas to study the most compelling questions at the intersection of physics and astronomy.

The committee that wrote the report added that another proposed mission to detect gravitational waves using the Laser Interferometer Space Antenna (LISA) should eventually become the flagship mission of Beyond Einstein, given that it is likely to provide an entirely new way to observe the universe. However, LISA needs more testing before a launch can be planned, whereas the Joint Dark Energy Mission is ready now for a competitive selection of mission concept proposals.

Prompted by Congress and the Office of Science and Technology Policy, NASA and DOE asked the committee to assess the five proposed mission areas and recommend one for first development and launch. NASA's Beyond Einstein program, set to begin in 2009, is comprised of two astronomical observatories, Constellation-X and LISA, as well as a series of probes: the Inflation Probe (IP), the Black Hole Finder Probe (BHFP), and JDEM.

"All of the mission areas in the Beyond Einstein program have the potential to fundamentally alter our understanding of the universe," said committee co-chair Charles F. Kennel, distinguished professor and director of the Environment and Sustainability Initiative at the University of California, San Diego. "But JDEM will provide direct insight into a key Beyond Einstein science question, and is the most technically feasible option for immediate development."

Of particular interest to researchers is whether the acceleration of the expansion of the universe varies over time. So far, three specific mission plans have been studied in this area: the Supernova Acceleration Probe (SNAP), the Dark Energy Space Telescope (DESTINY), and the Advanced Dark Energy Physics Telescope (ADEPT), but the eventual JDEM could be any one of the three or be based on a different option altogether.

The committee found that the underlying technology for a dark energy mission is, for the most part, in the prototype phase, and will require less development than most of the other missions. The potential gains for JDEM also outweigh its scientific risks, such as the possibility that the mission may not provide substantial insight beyond that provided by telescopes on the ground. The report recommends that NASA and DOE proceed immediately with a competition for mission proposals that will investigate the nature of dark energy with high precision.

The committee also recommended that NASA invest additional Beyond Einstein funds in technology development of the LISA program. LISA, which is funded through a partnership between NASA and the European Space Agency (ESA), is designed to detect gravitational waves arising from, among other phenomena, the merging of black holes.

The committee found that LISA will open up new ways of observing the universe, but must await results from ESA's "LISA Pathfinder" mission first. Scheduled for launch in 2009, LISA Pathfinder will test many of the new technologies required for the LISA program. Yet, some critical technologies, such as extended use of micro-Newton thruster technology, will not be tested. The report recommends that the development of these technologies should be a high priority for the Beyond Einstein program.

The report indicates that the three elements of Beyond Einstein that are not being recommended for immediate implementation are still important endeavors that should receive continued support. The committee found that because the Constellation-X mission is a general-purpose x-ray observatory capable of broad contributions to astrophysics, it should be funded and assessed in a broader context than the Beyond Einstein program.

The Black Hole Finder Probe and Inflation Probe missions will also make important scientific contributions; however, because of scope and technical readiness issues, they fell behind JDEM and LISA. The committee recommended that Constellation-X, Black Hole Finder Probe, and Inflation Probe receive continued support to prepare them for the next decadal survey of astronomy and astrophysics.

The study was sponsored by the U.S. Department of Energy and NASA. The National Academy of Sciences, National Academy of Engineering, Institute of Medicine, and National Research Council make up the National Academies.