The top U.S. science advisory body says it's time to figure out what this dark energy stuff is, anyway. 
In an eagerly awaited report, the National Research Council laid out its recommendations Wednesday for which major space-science missions NASA should next pursue, as part of a long-term plan dubbed "Beyond Einstein." The conclusions will likely help guide the agency's investment for years to come.
Coming in at top of the list is a probe investigating the phenomenon of dark energy, and its presumed role in affecting the expansion rate of the universe over time.
Three different concepts for the proposed probe, known as the Joint
Dark Energy Mission, have been studied by NASA, but all three would attack the problem by focusing on supernovae created by the explosions of white dwarf stars.
Because these events are fairly regular in their properties, they can serve as good measuring posts for the size and expansion rate of the universe, astronomers say. Observing this kind of stars helped lead two separate sets of astronomers to the idea of dark energy in 1998.
However, the concept remains shrouded in speculation, with astronomers having a better sense for what dark energy does than for what it actually is. According to recent observations, the universe seems to be expanding at an accelerating rate, and scientists believe this mysterious dark energy – which could account for as much as 70 percent of the universe's total energy – is responsible.
The JDEM probe, scientists hope, would help fill in those gaping holes in our understanding.
The National Research Council wrote that a separate mission designed to observe gravitational waves should eventually take precedence within the Beyond Einstein family of projects, but noted that it was farther away from readiness.
(Photo: Supernova SN 2006dr, of the type that would be studied by the JDEM probe, shining brightly next to the central core of the spiral galaxy NGC 1288. Credit: European Organisation
for Astronomical Research in the Southern Hemisphere)
