Volume 4, Issue 32 October 2007
Listening for Alien Life
The Allen Telescope Array, dedicated on Oct. 11, 2007, is designed to conduct traditional astronomy and to search for signs of intelligent life elsewhere in the universe. Photo: courtesy of UC Berkeley
In a quiet valley north of California's Mount Lassen stands a peculiar manmade forest. Here, 42 metal dishes, each roughly the height of a two-story building, tilt their bowls toward the sky amid a landscape of green pines and yellow brush. This futuristic assemblage, scattered across UC Berkeley's Hat Creek Observatory, is humanity's leading effort to find intelligent life in outer space.
The Allen Telescope Array (ATA) is the first astronomical observatory designed to search for alien beacons full time. Day and night, its broadband radio receivers scan the skies for "we are here" messages from other solar systems.
The array is the culmination of years of work by husband and wife astronomers Jack Welch and Jill Tarter. A UC Berkeley radio astronomer and professor of the graduate school, Welch served as director of the Hat Creek Observatory for more than 24 years. Tarter leads the SETI Institute, the world's most rigorous search for extraterrestrial intelligence.
Jack Welch examines the feed of an ATA antenna alongside a former student. Photo credit: Rick Forster
Both Welch and Tarter decided early in their careers that the universe might be home to other forms of life. In 1968, Welch helped discover the fact that water molecules are scattered throughout the universe, bolstering the chances of encountering beings elsewhere. "Water is the molecule of life," he says.
Tarter got hooked while still a graduate student at Cal. A professor suggested she read NASA's Project Cyclops study, a plan for building a vast array of large radio telescopes to search for extraterrestrial intelligence. "It's a very dense engineering document, but it was a page turner for me. I learned something I had never thought about before-after all the millennia of asking the priests and philosophers whether we are alone, I lived in the first generation of humans that could try and do an experiment to answer that question. How could I pass up a chance to work on such a profound problem?"
This mutual interest led Welch and Tarter to meet. Welch was asked to fly a guest from NASA Ames Research Center to Hat Creek in his small plane. Tarter came along for the ride. The two have collaborated in work and life ever since.
Astronomer Jill Tarter of the SETI Institute at Arecibo Observatory in Puerto Rico, where she conducted observing campaigns several times a year until 2004. Photo: courtesy Jill Tarter
Tarter spent the first decades of her career relying on scraps of observing time on other people's radio telescopes. It made her research frustratingly slow. She had compiled a list of hundreds of thousands of stars that might harbor life, stars similar in longevity and temperature to the sun, but had managed to examine only 1,000 or so.
Then, in the late 1990s, the SETI Institute held a series of workshops to chart the course of future extraterrestrial intelligence research. The idea for the ATA first arose from these meetings.
The ATA's design balances scientific utility and economy. At 20 feet wide, each dish is a fraction of the size of big radio telescopes, and relatively inexpensive to build. But as a group, they are spread over a square kilometer of real estate. Together, the dishes produce an exquisitely detailed image of a broad swath of the radio sky in any given instant, and promise to make the search for extraterrestrial intelligence hundreds of times faster than before.
Jill Tarter explains the SETI signal processing hardware on the ATA to Steve Trimberger of Xilinx Inc., a generous telescope supporter. Photo: courtesy Jill Tarter
Though inspired by the search for otherworldly civilizations, a partnership between the SETI Institute and UC Berkeley's Radio Astronomy Laboratory has turned the ATA into a multi-tasking radio astronomy facility. Because the array detects signals at an extremely wide range of frequencies, it can perform SETI's searches and collect data for traditional astronomy projects at the same time. These projects include creating a map of local interstellar hydrogen that could shed light on the evolution of the universe, and locating transient radio sources that have been predicted but not yet found.
The 42 dishes in the ATA start observing this month. With additional funding, the project will eventually total 350 dishes. Tarter and Welch know it could take some time to complete the array. But both are convinced it's just the right tool for their search.
Says Welch, "There's got to be life out there in some form. We just have to keep looking for it."