Can We Hear Them Now?
Speak up, space aliens. These 42 new radio telescopes are all ears.
- By Tony Reichhardt
- Air & Space magazine, July 2007
IN The Cascade Mountains of northern California, within sight of Mt. Shasta’s snow-topped, 14,000-foot peak, lies the high valley of Hat Creek, where they say the fishing is good. People come here in the summer for a little R&R among the tall trees, away from modern technology and its discontents. Strange, then, that the valley should also be home to one of the most futuristic projects on the planet—the Allen Telescope Array, the first radio observatory built expressly for the Search for Extra-Terrestrial Intelligence. The late physicist Philip Morrison, one of the founding fathers of SETI, called the search “the archaeology of the future,” an attempt to learn whether civilizations more advanced than ours exist. Some might call that possibility unlikely. Then again, so may be the long-term survival of humanity. And we still hold hope in that.
On this warm day in March, Jill Tarter is sitting at a desktop computer, studying sensitivity data from telescope 2H as it pans slowly across the sky. Outside, visible through the glass doors of this modest office/utility building, are 42 identical dish telescopes, each the size of an apple tree. Only 2H is moving. The orchard’s pattern appears random, with dishes facing all directions. In fact, the arrangement is as random as a computer program can make it.
Tarter writes something down, then goes into an adjoining room to pull one cable from an electronic console and plug in another. Telescope 2H is done; time to test another. If you didn’t know better, you might guess this is the IT department for a satellite radio company, and that Tarter is the head geek. Look around, though, and you’ll see something else is afoot. In the electronics room, one of the refrigerator-size computers sports a bumper sticker with the question, “Are We Alone?” and a Web address for the SETI Institute in Mountain View, California, where Tarter is the director for SETI research, “chief cheerleader” (her words) for the Allen Telescope Array (ATA), and the leading figure in her small and peculiar field of science (as well as a contributing editor of Air & Space/Smithsonian). Paul Horowitz of Harvard, probably the second most prominent SETI-ologist, remarked in 1988: “Jill Tarter has been plugging away at SETI for at least a decade, rebutting bad ideas, going around actually doing SETI on the world’s telescopes instead of talking about it, basically calling everyone’s bluff and keeping the subject from becoming too theoretical.”
To “do SETI,” scientists like Tarter use radio telescopes (usually) to either scan the sky or point at selected sun-like stars, listening for signals that would be recognizably artificial in origin. The rationale is that some extraterrestrial society more advanced than ours, with more powerful transmitters, might be broadcasting a signal—perhaps a series of dots and dashes, or a continuous tone—that would stand out from the natural radio emissions of stars and galaxies. Radio waves are a logical choice for interstellar communication because they cut through the gas and dust between stars. It’s called the search for extraterrestrial intelligence, though it isn’t really. “We look for evidence of somebody else’s technology,” Tarter has said. “I don’t know how to find intelligence.”
She is good-humored and friendly, if slightly brisk in manner, as though constantly aware she’s behind in her work. She likely is: These are busy days.
Tarter has driven the five hours from her SETI Institute office in Silicon Valley to Hat Creek (the license plate of her Saab sedan reads “SETI”) to spend a week running checks on the ATA telescopes. She and her husband, Jack Welch, a radio astronomer at the University of California at Berkeley and a key figure in designing this array, often make the trip in his Cessna 210 to save time. She flies too, but didn’t on this trip.
Tarter worked on her first SETI project, Berkeley’s SERENDIP 1, as a grad student at Hat Creek in the 1970s. She had grown up reading science fiction, and can’t remember ever not believing in the possibility of extraterrestrial life. What prompted her to make it the focus of her career was a 1971 NASA study called Project Cyclops, which outlined a practical approach to building an observatory for radio SETI. Although Cyclops’ array of 1,000 telescopes was deemed too expensive to build, the idea had great appeal to Tarter, and it set her on an unusual course for a scientist, where the chance of getting solid results (an alien signal!) would remain slim, but there would always be plenty of work to do improving detection methods. Like almost every search conducted to date, Tarter’s first venture into SETI 30 years ago had to piggyback on another radio astronomy project. Now, at 63, she finally has a dedicated observatory in the Allen array, like a lifetime renter moving up to buy.
More than 100 SETI searches have been conducted since 1960, with no signal detected. That sounds conclusive, but it’s not. Most searches have been very limited—a patch of sky here, a narrow slice of the radio spectrum there. It’s as though a driver going cross-country had tuned to a single radio channel for a few seconds, heard nothing, tried two more channels the next day, heard nothing, and concluded that the United States has no radio stations.
With Tarter in the lead, the privately funded SETI Institute (Congress cut all NASA funding for SETI in 1993) conducted the most comprehensive search to date, called Project Phoenix, from 1995 to 2004. Phoenix targeted about 1,000 sun-like stars, spending a few minutes listening for radio signals from each. “There wasn’t a transmitter pointed our way when we looked,” says Tarter. “Does that mean there’s no technological civilization? I don’t know. That’s a much harder conclusion to draw.”
Phoenix took 10 years because the SETI-ologists had to borrow observing time, a week here and a month there, on other people’s radio telescopes, including the 1,000-foot-diameter Arecibo dish in Puerto Rico and the 210-foot dish at Parkes, Australia. Tarter’s new array of telescopes will do SETI operations all day, every day. It will also be used by scientists for conventional radio astronomy—Berkeley is partnered with the SETI Institute on the project—but this time, they’re the ones who will be along for the ride.
Phoenix listened for signals over a range of three gigahertz—a wide swath of radio spectrum by SETI standards. The ATA will monitor 10 gigahertz continuously, targeting 1 million stars with enough sensitivity to detect an Arecibo-size transmitter broadcasting from 1,000 light-years away. That is, if the array grows from the current 42 to the planned 350 telescopes. Any radio telescope’s sensitivity to faint signals depends on its total collecting area, whether it’s a giant single dish like Arecibo or lots of little ones. The ATA philosophy is to build many small dishes as cheaply as possible, then rely on sophisticated software to process the signals.
Economy is a necessity for the project, which has only seven people working at the Hat Creek site. They buy off-the-shelf when they can, invent when they must. The small secondary reflector attached to the front of each dish, along with the telescope’s electronics, is covered with a shroud that’s fabric on top, aluminum below. The project’s engineers had to test all kinds of fabrics before they found one that kept out water but let in radio waves.
Tarter opens the shroud from the aluminum bottom and we poke our heads up inside, where we’re hit by a blast of hot air. Temperatures in the valley routinely top 100 in summer, and the sensitive electronics have to be kept cool (mini-refrigerators used in cell phone towers turned out to work nicely).
Inside the shroud is a spiky, silver-gold device that looks like an artificial Christmas tree. This is the telescope feed, which Tarter says reminds her of something from Flash Gordon. This particular design is another ATA innovation, and a crucial one. The feed is where radio energy collected by the dish is focused and converted to a signal containing the multi-frequency SETI data, which is then sent via fiber-optic cable to computers for processing.
The brains of the telescope array are inside the computer building. That’s where digital signals from the individual telescopes are sorted and manipulated, turning this field of small dishes into a large and powerful phased array (see “How Things Work: Phased-Array Radar,” June/July 2006). Because radio waves from a target star reach any two telescopes at slightly different times, the peaks and troughs of the waves are slightly out of synch, or phase. The SETI computers can artificially shift the phases to match up, effectively combining the waves and boosting the signal. Or, equally useful, a signal can be canceled out by phasing up the troughs in the waves. That enables the team to filter out, for example, an annoying, beeping satellite known to pass over Hat Creek every night, which otherwise might be mistaken for a broadcasting alien. For a computationally intensive program like SETI, that’s huge.
The more antennas, and the more random their pattern (hence the deliberately scattered placement), the better the technique works. “It’s a lot of vector algebra, that’s all,” says Tarter. Her bachelor’s degree from Cornell was in engineering physics, and she’s very much a hands-on experimentalist. I ask her if, despite the workload, she likes all the tinkering and testing. “Sure,” she says. “The frustrating thing is, I want it now. There are observations I want to make.”
In fact, now that the first section of the array is in place (the 42nd antenna was installed in February), the ATA will make its first observations this summer. The dishes will be pointed toward the center of the Milky Way galaxy, which is thick with stars. The bad news is that most of them are extremely far away—the most distant extraterrestrials would need a transmitter 20,000 times more powerful than Arecibo’s to be heard. It’s a long shot, but worth trying while the array is still under construction, partly because such a broad survey has never been done.
Meanwhile, the catalog of candidate stars (those most likely to be orbited by habitable planets) has grown to 250,000, and will eventually reach 1 million by the time the array is finished. As for when that might be, it depends on money.
“We’re struggling, absolutely struggling,” Tarter says on the subject of fundraising. So far, the man for whom the array is named, Microsoft co-founder Paul Allen, has bankrolled the project to the tune of $25 million. His last donation came in the form of a challenge grant, which would fund the array through 206 dishes if the SETI Institute could raise $16 million on its own. It fell $7 million short. The deadline was extended, but the institute is still about $30 million away from financing the full 350-dish array. And the longer it takes to raise the money, the longer the delays in construction, and the more expensive it all becomes.
Between the telescope testing, the software debugging, and the money worries, Tarter doesn’t have a whole lot of time to think about alien contact. That’s another odd thing about SETI: Even though a positive result would be among the most exciting discoveries in human history, there’s a good chance that the content of any message would be indecipherable. We’d know only that someone is out there, trying to communicate. And that would begin a whole new field of inquiry.
It’s hard to predict if or when that day will come. But should the ATA scientists ever hear a signal and verify independently (and in confidence) that it’s not from Earth, here’s what would happen: First they’d have their own private celebration. Every time the Phoenix team lugged its equipment to a radio telescope in Puerto Rico or Australia, says Tarter, “we always brought along champagne and kept it on ice.” Then, as a courtesy, they would inform the major ATA donors. After that, they’d e-mail an official notice to the scientific community describing the discovery. They’d also send off a scientific paper to an astrophysics journal. Much of that paper is already written; only the details are missing.
Then they’d call a press conference.