…continuedSETI Searches Today
A lot of SETI action has been happening elsewhere than at Arecibo. In March 1998, a near-copy of the earlier SERENDIP III receiver began piggybacking on the 64-meter radio dish at Australia's Parkes Observatory, the largest radio-astronomy telescope in the Southern Hemisphere. Run by the SETI Australia Centre (University of Western Sydney Macarthur), Southern SERENDIP was upgraded in 1999 from 8.4 million to 58.8 million channels. Each channel is 0.6 hertz wide, for a total bandwidth of 35 MHz. This band can be tuned to listen at any frequencies between 1.2 and 1.5 GHz, while the rest of the telescope goes about its regular programs such as hunting for pulsars and surveying hydrogen clouds in the Milky Way.
The project has been ticking along ever since. In May 2008, SETI Australia Centre director Frank Stootman gave this update: "We are actually in the process of revamping the machine as I write. The machine is back from Parkes in our lab for maintenance and upgrading. We have added a new control computer and written modern control software running under Microsoft XP. Our hope is to bring it back online by July/August.
"The new software will improve the communication between Serendip and the outside world. We are producing client software which will allow a limited number of sites to have direct access to data as it is produced. This (hopefully) will interest museums particularly. We intend to add instantaneous data analysis to the client software to make the whole adventure more immediate."
Strengths: Southern SERENDIP is surveying a large fraction of the entire sky, including the southern half of the celestial sphere. It can therefore scan most of our Milky Way galaxy's enormous volume most of which lies south of the celestial equator and is out of Arecibo's sight.
Weaknesses: The antenna has a fifth the diameter (and thus 1/25 the collecting area) of Arecibo. And as with other piggyback programs, there is no real-time followup.
Starting in the early 1980s several sky surveys were carried out by Paul Horowitz of Harvard University and his graduate students, using a 26-meter dish in the town of Harvard, Massachusetts. The culmination of these efforts was Project BETA (Billion-channel Extra-Terrestrial Assay). Supported by The Planetary Society and private donors, Horowitz and his team systematically swept the sky from declination 30° to +60° four times from October 1995 until March 1999, when one of the antenna's mounting gears broke in a wind storm.
Project BETA scanned a very wide frequency band, from 1.40 to 1.72 gigahertz, at 0.5-hertz resolution. This frequency range has been dubbed the "water hole" because it is marked on either end by important emissions from hydrogen (H) and hydroxyl (OH), components of the water molecule. The hope is that extraterrestrials wishing to be noticed might also choose a frequency somewhere in this well-marked band, water being so important to life. Even if the ETs aren't thinking this way, this band is wide enough that it has some chance of catching a transmitter at a random frequency chosen for reasons we can't guess.
Following an appeal to its members, The Planetary Society raised funds toward repairing the dish and getting Project BETA back on the air. But straightening out the surface of the dish, a high-precision job, turned out to be more costly than expected, and so the repair project ended. Planetary Society executive director Louis Friedman says the society decided to shift funding from the dish repair to Horowitz's new optical SETI project, described below. Sadly, the historic but now useless radio telescope was finally dismantled in May 2007.
Strengths: BETA scanned 68 percent of the celestial sphere across a wide frequency band. This is the optimum kind of SETI strategy if, as seems most plausible, the alien transmitters that we might actually be able to hear are very rare but very powerful (see "Smarter SETI Strategy.") BETA also used elegant methods to check interesting signals, reject false alarms, and perform real-time followups of potential genuine signals before fading due to interstellar scintillation could take effect.
Weaknesses: A small, relatively insensitive dish.
META II becomes Southern SETI
BETA replaced the more limited Project META (Million-channel Extra-Terrestrial Assay), built by Horowitz and his students in 1985 and installed on the same Harvard radio telescope. From 1986 to 1991, META searched 60 percent of the celestial sphere in narrow, carefully chosen frequency bands very close to the 1,420 MHz hydrogen frequency and its second harmonic (2,840 MHz).
META's hardware was duplicated in the Southern Hemisphere by the Instituto Argentino de Radioastronomia (IAR), with funding from The Planetary Society. Called META II, this search used a pair of 30-meter antenna dishes near Buenos Aires, starting in 1990, to survey nearly half the sky repeatedly between declination 90° and 10°. Paralleling the first META, it monitored 8.4 million very narrow, 0.05-hertz channels close to the hydrogen frequency and its second harmonic. In 1997 it was upgraded to newer technology.
The director of META II, Guillermo Lemarchand, said in August 2004 that the project was then observing natural hydroxyl masers in interstellar gas clouds, in case ETs are using these as natural signal amplifiers. Literally "astronomical" signal-strength boosts of up to a trillion times are theoretically possible through this means, though only in fixed, extremely narrow pointing directions.
In 2009, thanks to another grant from The Planetary Society, the META II back end was being replaced with a state-of-the-art SERENDIP V system, designed by Dan Werthimer's team at Berkeley. The SERENDIP V receiver and signal processor will expand the Argentine search from 8.4 million to 128 million simultaneous channels, and from a total bandwidth of 0.42 MHz to 80MHz with wider channels. This is crucial; the old bandwidth was so narrow that a signal could have been detected only if the alien transmitter was carefully compensating for Earth's motions, hardly likely.
At the same time, LeMarchand was working with international partners to develop the optimal software for operating the system. As of 2008, The Planetary Society was estimating that the SERENDIP V upgrade would be on the air in summer 2009.
The Argentine project is currently named Southern SETI; the META II moniker has been retired. "If anyone is hailing us from the center of our galaxy, chances are that it will be the new Southern SETI that will hear the call," wrote Amir Alexander in the Nov.-Dec. 2008 issue of The Planetary Society's magazine, The Planetary Report.
Strengths: Southerly location, which allows most of the Milky Way's bulk to be scanned, not just the Northern Hemisphere's fringe. State-of-the-art signal detection and processing (once the SERENDIP V upgrade is online).
Weaknesses: The small antenna aperture means low sensitivity.
Other projects have been carried out around the world in recent years. Radio astronomers in Italy piggybacked a 24-million-channel version of the SERENDIP IV spectrum analyzer onto a 32-meter dish in Medicina, run by the Institute of Radioastronomy in nearby Bologna. SETI Italia covers 15 MHz of bandwidth at 0.6 Hz resolution. "It is planned, within a period of less than six years, to survey at least 50 percent of the sky observable from Medicina," wrote Stelio Montebugnoli, chief engineer of the Medicina station, in 2002. In addition, says Montebugnoli (August 2004), "At present I am developing a low-cost spectrum analyzer with 64 million channels and 50 MHz of input bandwidth."
SETI Italia is using a new signal-processing algorithm that can recognize a wide variety of complex artificial signals, not just the simple, narrowband ones that most SETI programs listen for. The so-called KLT transform "is able to detect any kind of radio signals embedded in the noise," Montebugnoli told a Spanish interviewer (August 2004). "We still have a lot of work to do to make this transform efficient. . . . When we will have it working more efficiently I am planning to distribute it free." Radio engineers at the institute are also developing better algorithms for separating interstellar signals from Earthly noise in piggyback SETI data.
And More. . .
In April 2010 the European agency ASTRON in the Netherlands announced that its LOFAR array (designed for high-resolution radio astronomy at poorly explored, relatively lowfrequencies) would embark on a SETI project targeting nearby stars. LOFAR was still under construction but already producing science images. "The first phase of this SETI program will study how contamination from terrestrial transmitters can be weeded out and show the sensitivity of LOFAR for SETI work," according to a press release. "An extended program of looking at the nearby stars is then planned. The first high-spectral resolution spectrum in the test program has just been obtained."
At NASA's Jet Propulsion Laboratory, a small, internally funded group has carried out a pilot study for a wide-sky SETI survey in hopes of getting back in the game years after Congress pulled the plug on the original NASA SETI projects. Steven Levin and a few others at JPL worked on a proposal for a new, updated version of NASA's wide-sky survey the project that the SETI Institute did not pick up after federal funding for it ended in 1993.
The potential power of such a survey has grown greatly since then, what with a decade of signal-processing advances. "We're working on a pilot study now," Levin told Sky & Telescope in September 2004. Using a spectrometer loaned by Dan Werthimer (University of California, Berkeley), the group was using a 34-meter dish to scan along the galactic plane with a 2.5-megahertz bandpass, "to learn what we could do with a 20-gigahertz bandpass," Levin says. The scan covered the star-dense band of sky within 2° or 3° of the galactic equator. Its spectral resolution was 2.4 hertz per channel. Levin said at the time that the group hoped to follow up with a 100-MHz-wide survey, with the ultimate hope of listening to the entire microwave spectrum from 2,000 to 22,000 MHz a vastly greater range of frequencies than any survey has yet attempted.
The sensitivity axis is scaled in units that indicate the relative volume of space (number of stars) examined in a given direction for an alien transmitter of a given power. The graph shows, for instance, that SETI@home I (a narrow extension of Project SERENDIP IV) listened only near a frequency of 1.420 gigahertz, but that it surveyed a greater volume of space at this frequency than was ever looked at before.
There are more parameters to consider than the three graphed here for example a signal's frequency drift, on-off duty cycle, and polarization. Plotting them all, says Jill Tarter of the SETI Institute, would require a 9-dimensional graph. The 'haystack' to be searched for the 'needle' of an alien signal is huge indeed."
Since the early 1960s, according to a count by Jill Tarter of the SETI Institute, there have been 101 much more fragmentary or limited SETI projects of one type or another. Many of these were run by astronomers who had access to spare time on radio-astronomy gear and a particular brainstorm to try out. Others looked at data that were collected for other purposes for signs of anything artificial. Tarter has posted her list of historical SETI programs.
And yet, estimates Guillermo Lemarchand, all the searches to date have looked at only 1014 that's a hundred-trillionth of the "cosmic haystack" of frequencies, sky directions, and other parameters that need to be sifted for the "needle" of an artificial signal.
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