123Compute.Net |
|
|
|
|
|
|
Tools |
|
September 29, 1998
By William J. Broad
RECIBO , P.R. -- "Sorry guys," Jill C. Tarter said, cutting off chitchat around the control panel, eager to hunt for alien civilizations. "We have the telescope."
Outside in the fading light, surrounded by dense jungle, the receiving dome on the world's largest radiotelescope wheeled into position. It fixed on Barnard's star, a scant six light-years away, the closest star to Earth in the Northern Hemisphere. Closeness meant it had been searched before. But now, the great dish antenna of the Arecibo observatory began to gather in a riot of faint signals, giving the star its most discriminating look yet for hints of invisible planets and intelligent life.
Tense with concentration, Tarter, 54, closely examined the colored spikes that slowly materialized on her monitor. Each was a candidate, a possible hello from afar. But in the next hour and a half, she, a colleague and a nearby supercomputer rejected them, one by one. The signals turned out to be cosmic static and earthly interference.
She showed no sign of frustration -- no sigh, joke or frown. A true believer, she just plowed ahead to examine a night full of stars, sure that some day there would be proof that humans were not alone in the universe.
The search for extraterrestrial intelligence, or SETI, is at a turning point after nearly four decades of hard work. With the arrival here of Tarter and her crew from the SETI Institute in Mountain View, Calif., the field has reached a high point in terms of telescope sensitivity, a top goal of the alien hunters.
But it has found no extraterrestrials so far, despite forecasts that they should have been discovered by now. Instead, it has probed the heavens with regularity and heard nothing but a dead silence.
While pressing the hunt here at Arecibo, Tarter and her peers around the globe are engaged in quiet debate and soul searching over how to proceed. New ideas and strategies are being weighed, including expansions that would enhance telescope sensitivity and widen the hunt to more stars -- perhaps 100,000 rather than the 1,000 now targeted.
"When you get far into a project and haven't found what you're looking for, it gives you pause," Seth Shostak, a SETI Institute scientist, said as he trudged down a hillside into the lush bowl that holds the telescope's huge receiving dish, the size of 26 football fields.
Does the silence bother him?
"It's a funny thing," Shostak replied. "You'd think it gets old. But it doesn't. The equipment keeps getting better and the odds keep getting better, which never happens in Vegas. Also, there are always new ideas. This is a field with new papers, new meetings, new people -- which is remarkable considering there is no data. So for me, it's not discouraging at all."
Close up, the great antenna was a grayish sea of thousands of perforated aluminum panels. High overhead, a cable car hauled engineers to the central receiving dome to do maintenance. Shostak strode under the dish into dim sunlight and surprisingly dense foliage.
Any boa constrictors down there?
"The worst thing is the mud," he called back confidently.
Like most SETI enthusiasts, Shostak and Tarter believe it is just a matter of time before earthlings use such antennas to make contact with aliens. Their faith is rooted in numbers, big ones. The Milky Way is estimated to have 400 billion stars, including the Sun. SETI scientists believe that many of these stars have planets orbiting them as well as advanced forms of life -- an idea skeptics deride.
Alien civilizations in the galaxy are likely to number anywhere from 10,000 to one million, SETI enthusiasts say. If the higher density is right, that means advanced beings would inhabit about one in every 400,000 stars. The implication is that even a slow, detailed, comprehensive search from Earth would be mostly a wasteland of late nights, false leads and frustration.
"It may look empty, but it's not," Shostak said as he sipped a root beer in the observatory's cafeteria, eager to cool off from the wet heat outside.
"O.K., maybe this is a hopeless task, maybe it's impossible," he conceded. "On the other hand, maybe it's like discussing the possibility of whether there's a continent between Europe and Asia in the cafes of Segovia in the 1400's. Until you do the experiment, you don't know."
The first SETI hunt began in humble circumstances in the Allegheny Mountains of West Virginia. In 1960, Dr. Frank D. Drake, a young scientist at the National Radio Astronomy Observatory there, used an 85-foot antenna to listen around a few stars for alien transmissions. Ever since, a main SETI strategy has been to wield increasingly big radiotelescopes, their size allowing them to gather increasingly faint signals. The dish antenna at Arecibo, 1,000 feet wide, is the biggest of them all.
SETI work started here with a bang. In 1974, at the urging of Drake, who then ran the observatory, the newly upgraded dish at Arecibo was used to beam a powerful, three-minute message at M13, a dense cluster of hundreds of thousands of stars orbiting the Milky Way. The message was a simple graphic showing the telescope as well as facts about the solar system and humans. The message is still zooming outward. At the speed of light, it will reach M13 in about 21,000 years. A reply from any aliens in that neighborhood would presumably take a similarly long time.
Tarter got hooked on the field in the mid-1970's, soon after the message was sent. She was then a young astronomer at the University of California at Berkeley. After reading a SETI report, she teamed up with another astronomer to hunt for aliens with the university's 85-foot telescope.
"It was brave of Jill," Drake said in his autobiography, noting that SETI work back then could hurt a developing career.
By 1985, Tarter was a senior SETI scientist at the National Aeronautics and Space Administration. She and her colleagues built powerful computers to sift through cosmic and earthly interference and lined up many radiotelescopes, including Arecibo. Their goal was to survey 1,000 nearby stars, all within 200 light-years of Earth.
In 1992, the big search was ready to start. And Drake, the SETI pioneer, gave it a drum roll in his autobiography, "Is Anyone Out There?" (Delacorte Press, 1992, written with Dava Sobel), saying the find of all time was imminent.
"This discovery," he wrote, "which I fully expect to witness before the year 2000, will profoundly change the world."
But the plug was pulled suddenly in 1993 when Congress decided that SETI was a waste of public money.
Undeterred, Drake and Tarter took the hunt private at the SETI Institute. They won substantial support from a handful of silicon moguls, capitalized on the $58 million the Government had invested in gear and forged ahead with the planned search. In 1995, they began roving from telescope to telescope.
Tarter, who heads Project Phoenix, as the hunt is known, is famous for her zeal. She was the role model for Ellie, the heroine of the 1997 movie "Contact," based on Carl Sagan's novel, starring Jodie Foster. The two met when it was filmed at Arecibo.
"She's a fantastic person," Tarter said of Foster. "She wanted to know what astronomers are like, and do they have big egos." She laughed.
Wearing sandals, her hair tied in a ponytail, Tarter along with her institute colleagues started observing here Sept. 9. It was the team's first return since the Federal plug was pulled. A new agreement gives them 2,000 hours of observing time, or about a half-year's worth of 12-hour night shifts, which they plan to spread over the next few years.
A big lure is the new sensitivity of the telescope at Arecibo, which is run by Cornell University in cooperation with the National Science Foundation. Last year, work here was finished on a five-year, $27 million face lift that quadrupled the telescope's ability to pull in faint signals.
As always, the hunt focuses on close stars, since signals from their inhabited planets would be strongest. And it concentrates on ones similar to the Sun, the only star known to support life. Lastly, it tends to search older stars, since it assumes advanced life takes time to evolve.
At Arecibo, candidate alien signals are compared with readings from a radiotelescope nearly halfway around the world at Jodrell Bank in Britain. The comparison helps identify and rule out local earthly interference, which is exploding with the rise in satellites and cell phones.
"That is some hellacious thing," Tarter said as she glared at an interference spike. "It produces system indigestion."
Around midnight on Sept. 15, Tarter and Shostak were searching for aliens around EQ Pegasi, an unremarkable star 21 light-years away. Suddenly, the team's automatic search program started moving the telescope off the star, seeking to find out if a strong incoming signal was simply interference.
The signal died away, as it would if it originated from the star. And it returned when the telescope refocused on EQ Pegasi.
Rising out of their chairs, electrified by the drama, the two astronomers studied the signal's high rate of drift. That suggested the transmitter was based on either a spinning satellite or a rapidly turning planet.
"Had Jill and I stared any harder at that display screen, we would have bored holes in the phosphor," Shostak recalled.
Again, the telescope was moved off target as the computer sought to double-check the signal's place of origin. This time the signal stayed on, meaning it was from a satellite.
"It was a big disappointment," Shostak admitted the next day. "I thought, 'Hey, this is the big one.' " Only a few times before had the team had such a sense of being on the verge of discovery.
Days later, on Sept. 21, Hurricane Georges slammed into the area, uprooting trees, hurling debris that damaged some antenna panels and temporarily disrupting the alien hunt, now set to resume Thursday.
Their faith apparently intact, despite the long hours and decades of failure, the alien hunters are planning in their spare time a new generation of strategies and gear. A committee based at the SETI Institute, including Tarter, Shostak and 31 other experts, began meeting last year to chart a path into the future.
At the controls of the Arecibo search, Tarter became quite animated as she described futuristic arrays of hundreds and perhaps even thousands of small dish antennas tied to one another electronically, scanning the sky for the advanced civilizations she knows are out there.
"We have to grow this," she said of untried gear that one day might dwarf Arecibo in sensitivity. "You have to crawl before you walk."
Her ultimate dream is to build an observatory on the far side of the Moon, free of earthly interference, scanning the heavens for an unfamiliar hello. She wants to be there herself, at the controls.
Created 9/29/98.
Email comments and questions to webmaster@123compute.net.
Tools