It’s sort of the "Academy Awards" for deep space astronomy, except it only happens once every 10 years.
Last Friday a blue-ribbon National Academy of Sciences (NAS) committee released its recommendations for what types of telescopes astronomers should be building over the next decade. This offers to Congress, NASA and the National Science Foundation an exploration roadmap sanctioned by our nation’s top researchers.
What’s fascinating is that a decade ago, it would have been hard to predict what would have made it to the top of the list of cosmic mysteries now confronting astronomers.
In the 2001 NAS Decadal Survey report, the big questions were about the age, history and expansion of the universe; understanding the formation and evolution of black holes of all sizes; studying the formation of stars and their planetary systems; and understanding how the astronomical environment affects Earth. Significant inroads were made into some of these areas, or are awaiting pursuit by telescopes now under construction.
Taking a closer look at the top science goals for the upcoming decade, it seems that the fundamental physics of the universe takes center stage.
The top-ranked space mission, called the Wide Field Infrared Survey Telescope (WFIRST), would use three types of observations to characterize dark energy. Dark energy, an unimaginably weak energy field from the vacuum of space, is pushing the universe apart at an ever-faster rate. This “dark force” is so far from what would have been predicted that Mike Turner of the University of Chicago calls it “the most embarrassing number in physics.” Therefore, it arguably is the most perplexing phenomenon ever to confront modern science.
As monumentally profound as this mystery is, I find it dissatisfying. Scientists are delighted at putting ever-tighter error bars around their observations. If built and launched for an estimated $1.5 billion, WFIRST will help physicists eliminate some theories for dark energy. We’ll know what dark energy isn’t. But the resulting dataset might never explain exactly what dark energy is. Turner has even confessed that we simply may never know.
WFIRST will also look for Earth-like planets in the far reaches of the galaxy using a technique called microlensing. This will build up the knowledge base for the abundance of Earth-sized planets in space. But, again, it’s just statistics and error bars.
I also find this dissatisfying because the newfound planets won’t be close enough to us for follow-on observations to see if they have habitable conditions. Such a telescope will not take us any closer to answering the “L” world: Life in space. The mega-space telescopes needed for that task won’t be technologically ready for at least another decade, and the 2020 NAS survey report.
A brave new frontier that could burst open by the end of the decade is the ghostly realm of gravity waves. Spacetime should be ringing like a bell as black holes collide and supernova cores implode. Though gravity waves have not yet been detected in ground-based experiments, the NAS highly ranked the Laser Interferometer Space Antenna (LISA) because it would open up a whole new discovery space by detecting these whispers from massive objects gone wild.
But it will need a technological demonstrator precursor mission before anyone is willing to pony up approximately $3 billion for LISA. Planned for 2012 is the European Space Agency’s LISA Pathfinder mission that will test a series of ultra-high precision technologies on a small single spacecraft.
The front-runner in recommended new ground-based telescopes is the Large Synoptic Survey Telescope LSST (which also was on the to-do list in the last Decadal Survey). This machine is truly astronomical in every sense of the word. It will essentially survey the entire sky on a weekly basis.
For the first time ever astronomers will have a time-lapse color movie of the universe. It will capture wayward asteroids and comets, erupting stars, and anything else that moves or flashes in the night. Untold wonders await. The resulting 1,000-terabyte data archive will be a “treasure trove,” the NAS report predicts.
Ranked lower on the space observatory list, and a disappointment to the aspirations of high-energy astrophysicists, is the proposed $5 billion International X-Ray Observatory (IXO). Previously called Constellation-X, it ranked higher than the LSST in the last Decadal Survey. The IXO would probe gravity in the extreme, as it behaves around distant black holes. The IXO would also offer unique observational tests of dark energy and dark matter.
X-Ray astronomy has had a bumpy history. The first space observatory, Uhuru, opened up the X-ray universe in 1970. A series of high-energy observatories followed in the late 1970s. But X-ray astronomers had to wait another 20 years for the prolific Chandra X-Ray Observatory to come along. But a member of the 2010 Decadal Survey stated that IXO had a “limited potential for great discoveries.” Ouch!
Based on this history, what will the next Decadal Survey rank in 2020? I expect that by then the upcoming James Webb Space Telescope will fill in the opening chapter of the birth of stars and galaxies, by taking us back to within 200 million years of the Big Bang. But, given the fast pace of discoveries in exoplanets, I think the overarching quest will be for finding habitable worlds. I’m also sure that facilities like LSST will uncover remarkable new phenomena that need follow-up observations.