Why the Search for Life Drives Space Exploration
October 14, 2004
by Seth Shostak, Senior Astronomer, SETI Institute
They don’t wear coonskin caps, but they’re traipsing the wilderness nonetheless, working the margins of the Final Frontier.
The accomplishments, plans, and dreams of today’s space industry are showcased every year at a mammoth event known as the International Astronautics Congress (IAC). For an entire week, thousands of rocket engineers, space agency types, and satellite builders swarm like psychotic ants within the IAC’s cavernous convention halls, seeking the most exciting panels and plenaries. Furry fedoras and Bowie knives are out, while Italian suits and cell phones are in. Fact is – sartorial distinctions aside -- exploration today is not much different than when the pioneers slogged the west: difficult, dangerous, and oddly seductive.
Since 1971, SETI has been part of the IAC, and is usually celebrated with an entire day of presentations on the latest data, the technology, and the social implications of the search for intelligent life beyond Earth. This year’s Congress was in Vancouver, a Canadian city that crouches like a spangled jewel caught hard in the grip of mountains and sea. Appropriately enough, Vancouver bears the name of one of the 18th century’s most accomplished explorers.
The gamut of the SETI presentations ran from the latest telescope engineering to the language ET would use to signal. A comprehensive review of this material would likely exceed both reader patience and permitted word count, so I have cherry-picked a few items of note below.
The University of California’s SETI efforts continue to be expansive and ambitious. Graduate student Aaron Parsons described how the Berkeley group’s optical SETI search, which uses the Leuschner 30 inch telescope (situated on a hill a few dozen miles east of San Francisco), has so far checked out 7,500 star systems and 132 galaxies. Like other optical projects, the scheme looks for nanosecond flashes (one-billionth of a second or less) that momentarily outshine the light from a star.
Another effort to find pulses – of radio, rather than light -- is being initiated by the Berkeley team. It’s called Astropulse, and will rely on heavy compute power to correct for the unfortunate fact that the thin, hot gas of interstellar space smears radio pulses in time, turning them from short, sharp peaks into long, gentle hills, rendering them less obvious to a receiver.
Berkeley’s flagship SETI effort is SERENDIP V, the project that runs on the large Arecibo radio telescope, and the one supplying data for the SETI@home screen saver. SERENDIP V’s receivers boast nearly a billion channels (no doubt trumping your local cable service), and eventually will span 300 MHz of the radio dial. For comparison, that’s about 50 times more spectral space than a single TV broadcast.
About 1% of the SERENDIP data are distributed for number crunching by SETI@home. More than 5 million people have loaded up their computers with this popular screen saver, and every day two thousand more join the ranks.SETI@home’s collective reckoning power is that of a 65 teraflop machine, making it the biggest computer in the world. The distributed computer platform underpinning the screen saver is about to be opened up to other worthy projects such as cancer research, protein folding, and weather modeling.
Dave DeBoer, of the SETI Institute, gave an update on the Allen Telescope Array, now under construction in northern California. Within a few months, the antenna count of the ATA will grow to 32, a number that is sufficient to start some serious observing projects. Aside from a short laundry list of important astronomical studies, the ATA-32 will begin its SETI duties with a scan of the central plane of the Milky Way. This is where the apparent density of stars is highest of course, making it an obvious place to check out.
Thanks to its specialized beam-forming hardware and software, the ATA-32 will be able to look at 16 spots on the sky simultaneously. In other words, unlike SETI experiments of the past, this telescope will be able to examine many celestial targets at once. Eventually, the ATA, grown to hundreds of antennas, will be a screamer: at least two orders of magnitude faster than previous SETI searches.
Another approach to finding ET is to hunt for construction projects rather than signals. An idea that has intrigued the SETI community for decades is the thought that a truly advanced society might create a giant solar-cell array around its home star, providing an incredibly large energy source to fuel the good life. An array that completely surrounds the star is called a Dyson sphere, as it was physicist Freeman Dyson who first suggested the idea.
But the point is this: no energy converter, including solar cells, is ever 100% efficient. The array will warm up and its back side will disgorge infrared (heat) radiation into space. If you trip across a star that’s putting out more infrared than normal, well, you may have found a civilization that’s living large.
Richard Carrigan, of Chicago’s Fermi Lab, has been searching the data collected years ago by the IRAS infrared satellite, looking for such stars. He hasn’t found any good candidates yet, but this idea (which has been pursued by others) is obviously both intriguing and bound to benefit from better infrared telescopes to be launched in the near future.
The SETI sessions of the IAC were, as they always are, popular and provocative. But that’s no surprise. After all, what’s most alluring about the universe is the possibility that it’s not just 30 million trillion trillion cubic light-years of sterile real estate.