The hunt for planets orbiting other stars and capable of harboring life has reached a crossroads.
Never has the young field of "exoplanet" research been so ripe with promise, its practitioners say, with dozens of new planet candidates emerging every year. But now, with scientists ready to take the next step and discern whether any of these planets might have the potential conditions for life, the rug has been pulled from beneath them.
Two orbiting observatories seen as crucial to taking the measure of exoplanets and their atmospheres in detail have been scrapped. Budget cuts are one reason, but infighting within the scientific community made those cuts easier, according to several accounts. It leaves exoplanet hunters seeking creative solutions, such as retrofitting one space telescope with a special shade or sending up shoebox-size mini-observatories to nibble away at the job.
But some in the field can't help but feel concern that their dreams of one day being heralded as discoverers of new solar systems that later generations will explore may be slipping away.
"We really want to be the first generation to find planets" like Earth, says Sara Seager, an astrophysicist at the Massachusetts Institute of Technology (MIT) in Cambridge. "Now, it's not clear to me anymore that it will."
Part of the frustration is born of the field's unbridled success in the face of initial, deep skepticism.
When Wesley Traub prepared to head for his first exoplanet meeting in Colorado in 1990 – five years before the first confirmed exoplanet discovery – "I didn't tell anybody I was going because I was embarrassed," he says. "This was something you didn't talk about then" in the company of other astrophysicists.
Now he is the chief scientist for the National Aeronautics and Space Administration's exoplanet exploration program, and with each passing month, fresh detections from dozens of research teams point to a Milky Way galaxy teeming with solar systems utterly unlike our own.
More discoveries are in the pipeline. NASA's Kepler mission has added at least 1,235 planet candidates to the list for confirmation.
While detecting new planets is important, astronomers add, the field has reached a point where it must begin to study the atmospheres of exo-planets and comb them for gases that signify the presence of life.
The study of stars was at a similar point a century ago, notes Geoff Marcy, a pioneer of planet-hunting at the University of California, Berkeley. At first, scientists simply fit stars into categories based on their color and intrinsic brightness. But eventually they began to use starlight to understand a star's chemical compositions, which gave clues about their stage of evolution.
Similarly, it's now time to begin to understand the nature of exoplanets using the same tools – chemical fingerprints captured in light as it passes through or is reflected from an exoplanet's atmosphere.
Without these measurements, "studying the constitution of stars or planets is virtually impossible," Dr. Marcy says.
To get these measurements, however, planet hunters were relying on the two observatories no longer on the books.
One project, the Space Interferometer Mission, was supposed to launch in 2005. But budget cuts forced the date to slip. The project, which was included in two surveys intended to set NASA's priorities for the coming decade, eventually disappeared from the 2010 Decadal Survey as the community faced even tighter budget constraints.
The fact that $600 million was spent to develop a project that never came to fruition is "the most embarrassing, humiliating thing I've seen in my life," says NASA's Dr. Traub.
The second major loss is the Terrestrial Planet Finder (TPF), whose demise can be traced to flip-flops at NASA over the observatory's design, say Marcy and others.
It, too, had a high priority in previous decadal surveys and was expected to be launched as early as 2015. But internal bickering among the planet-hunting community over which design to support prompted its removal from NASA's to-do list for this decade.
Faced with the collapse of two keystone projects, researchers are becoming more inventive.
For instance, one space telescope that remains on the books, the James Webb Space Telescope, in principle could perform spectra-gathering duties on nearby exoplanets – something no one envisioned at the time the telescope was planned, says Matt Mountain, director of the Space Telescope Science Institute in Baltimore.
If less than 10 percent of the telescope's observing time is dedicated to exoplanets – and if the project adds a "star shade" flying in formation with the telescope to block light from an exoplanet's host star – studies suggest that the telescope could detect and characterize at least five Earth-like planets around nearby stars during five years of observing.
"This looks remarkably like what TPF-C would do," Dr. Mountain says, referring to one of the designs for the TPF.
Other researchers are busy thinking small.
Dr. Seager and Shawn Murphy, from the Draper Laboratory in Cambridge, Mass., are working with undergraduate and graduate students at MIT to develop a fleet of shoebox-size orbiting telescopes that would focus their attention on one or two nearby stars each. NASA is supporting the project, whose first prototype could launch on a space-station resupply mission as early as late 2012.