Early on February 11th, as dawn's rosy glow enveloped the summit of Mauna Kea in Hawaii, the domes of the Keck telescopes slid shut after a long night of observing. It had been a great run for Gerard van Belle (Lowell Observatory) and his small team. They'd used the two giant eyes together, pointing them in tandem at a handful of dim, cool dwarf stars scattered across the Hawaiian sky.
By carefully combining light beams from both telescopes, the observers had effectively transformed the two 33-foot-wide (10-m) primary mirrors into a single, much larger aperture 280 feet (85 m) across. This powerful pairing, called an interferometer, can discern the shape of a grape from 1,000 miles away. It enabled van Belle to resolve the disks of a few of his target stars — a feat not possible anywhere else.
Unfortunately, last week's all-nighter will be his team's final chance to harness the telescopes together. Last summer NASA managers quietly decided to stop funding the interferometer, and it will be mothballed in July. After that, the two Keck telescopes — which had been designed from the get-go to work together — will stare into the cosmic depths on completely separate schedules.
NASA's official position is that the interferometer has completed its primary task of revealing dusty disks surrounding nearby stars. Moreover, it's complicated and expensive to link the giant eyes through a system of optical pathways for just a few dozen nights each year. "This is tremendously bittersweet to me," van Belle laments. "I spent hundreds of nights on the summit from 1998 to 2001 getting this system to work."
For all its success, the Keck Interferometer has never lived up to its full potential. That's because it lacks a quartet of smaller telescopes, each with a 6-foot (1.8-m) primary mirror, that were to be installed alongside the towering twin domes atop Mauna Kea. These four "outriggers" would have given the interferometer the ability to image small patches of sky with unprecedented resolution — down to 30 micro-arcseconds, according to project scientist Rachel Akeson (Jet Propulsion Laboratory) — sufficient to spot Uranus-size planets circling nearby stars. It was designed to be the world's most powerful optical interferometer.
NASA gave the project a green light and funding in 1998. EOS Technologies in Tucson, Arizona, built the four telescopes years ago at a cost of about $15 million. But they never made it to the summit, victims of a sociopolitical struggle in Hawaii and NASA's shifting priorities in faraway Washington.
Mauna Kea, often translated as "White Mountain" because it's sometimes capped with snow, is a massive but dormant volcanic peak that rises 13,796 feet (4,205 m) from the Pacific Ocean. It provides what is arguably the premier site in the world for astronomical observations.
But it is also sacred to the Hawaiian people, and the stark, other-worldly summit — known locally as wao akua ("realm of the gods") is dotted with shrines, altars, and hidden burial grounds. Although professional astronomy is a strong driver of the Big Island's economy, lots of Hawaiians are nonetheless unhappy about having their sacred mountain peppered with gleaming observatory domes.
Tensions between the Big Island's native inhabitants and the University of Hawaii, which manages Mauna Kea's observatory complex, have simmered and occasionally boiled over for decades.
A master plan, approved in 1983, allows for no more than the 13 domes that exist there now. Whereas astronomers saw the outriggers as a extension of the existing facility, and thus part of Keck's two-dome footprint, native and environmental groups saw them as a cap-busting series of new structures. A revised master plan, agreed to in 2000 by the University of Hawaii and the Office of Hawaiian Affairs, would have permitted the construction of up to six Keck outriggers, but opponents challenged NASA's environmental assessment for the project.
The beginning of the end came in 2006. First, NASA withdrew its funding for the outriggers. The space agency had hoped to use the full-up interferometer as a pathfinder for two future efforts called Space Interferometry Mission and Terrestrial Planet Finder. But when these expensive, challenging missions foundered, so did enthusiasm for the funding Keck's interferometer.
The second and final straw followed a few months later, when a judge ruled that the expansion permitted by the revised master plan — and construction of the Keck outriggers in particular — could not go forward until a comprehensive assessment addressed environmental concerns for the entire summit. With funding withdrawn and a long legal battle looming, project proponents retreated.
NASA continued to fund the interferometer that linked the existing Keck telescopes, but the facility's scientific utility had been crippled. "The decision [to end funding] has been coming for years," Akeson explains. "The reality is that the interferometer has had to compete against all the other capabilities of Keck, and it requires the use of both telescopes."
A Second Chance?
Despite all the drama and disappointment, the effort and money expended on the outriggers might not go to waste. Keck officials have already turned the telescopes over to the U.S. Naval Observatory, which hopes to integrate them into its existing Navy Optical Interferometer in northern Arizona.
According to program director Don Hutter, adding the Keck cast-offs would be a huge boon to the NOI, which currently has seven telescopes with 20-inch (0.5-m) apertures in a Y-shaped array. If the Navy provides funding (and a decision on that is imminent), the NOI could be expanded from its current 80-m baseline to 100 m in just two years, improving its current 0.5-milliarcsecond resolution by a factor of two or three. Eventually the baseline could grow to 437 m — which would make NOI the world's largest optical interferometer.
In fact, van Belle has already hedged his bets. He recently left the Very Large Telescope Interferometer, close competition for Keck, and joined the staff of Lowell Observatory, which manages the Anderson Mesa site on which the NOI sits.
One last point: For a behind-the-scenes taste of Keck operations, be sure to check out Andrew Cooper's "Keck in Motion" time-lapse video, which includes shots of the interferometer's optical components running back and forth on precision rails. Cooper is an engineer, photographer, amateur astronomer, and telescope maker who lives and works on Mauna Kea.