Ever since its debut in October 2007, I've wanted to visit a curious collection of 42 radio dishes in northern California called the Allen Telescope Array.
Nestled in an arid, remote valley a few miles from volatile Lassen Peak, the ATA is the first radio "ear" built specifically to listen for broadcasts from alien civilizations. Searches for extraterrestrial intelligence (SETI) have been done before, but never on this scale.
Operated by the Radio Astronomy Laboratory (University of California, Berkeley), the ATA exists thanks to the generosity of Microsoft cofounder Paul G. Allen, whose foundation donated half of the $50 million start-up costs. The rest came from the SETI Institute (which managed fundraising for construction), the State of California (through UC Berkeley), National Science Foundation, and private donations. About half of the observing time has been dedicated to searches for extraterrestrial intelligence (SETI), while astronomers use the remaining time to study cosmic radio sources.
"We've been doing surveys to understand the transient and variable radio sky," explains Geoffrey Bower (UC Berkeley), who is the ATA's project director. "We search for new events such as radio-bright supernovae and gamma-ray-burst afterglows, and so far we've produced catalogs of radio sources over more than 10% of the sky. Moreover, he adds, the ATA is valuable as a platform for testing new instruments and observing techniques in ways that can't be done at larger facilities.
But keeping the array pointing skyward — let alone expanding to the 350 dishes envisioned for the full array — has been been problematic. The poor economy caused state and private funds to dry up, and expected long-term support from the NSF hasn't materialized. So on April 15th the ATA began a "hibernation," as project managers try to find the $1½ million per year needed to resume operations.
In a letter to SETI supporters issued on April 22nd, Institute CEO Thomas Pierson detailed the predicament. "Hibernation means that, starting this week, the equipment is unavailable for normal observations and is being maintained in a safe state by a significantly reduced staff."
The timing couldn't be worse. Radio astronomers had just started using the array to study dozens of tantalizing exoplanet systems discovered recently by NASA's Kepler spacecraft. "We'd like to extend this reconnaissance to the other more-than-a-thousand star systems that might have planets, of course," explains Seth Shostak (SETI Institute). "But more than that, we want to increase the frequency coverage of the best candidates." So far, Shostak says, they've mostly been examined only at the 21-cm wavelength known to SETI buffs as the "water hole".
The ATA's 42 anteannas, each 20 feet (6.1 m) across, have a combined collecting area equivalent to a single dish 65 feet (20 m) across. But because they're spread out over 1,000 feet, they can resolve the sky down to just a few arcminutes when used together as an interferometer — a big plus when trying to home in on individual stars and their planet systems.
One glimmer of hope for short-term funding might come from the U.S. Air Force, which could enlist the ATA for tracking orbiting satellites and large chunks of space debris. Unlike optical telescopes, the ATA can observe day and night — and when it's cloudy.
But something more robust is needed for the long term. "Right now, we are trying to raise $5 million to cover a two-year search of the Kepler worlds by [SETI pioneer] Jill Tarter and her team," Pierson writes. "This fabulous opportunity represents a fundamental shift to be able to point our instruments at known planetary systems, rather than at stars that might or might not host planets."
Beyond that, Bower estimates it'd take another $10 million to double the array's size and perhaps $50 million to get all 350 dishes built.