Science News - April 24, 2010

or antimatter-matter annihilation as a power source might produce such rays. But standard SETI strategy does not embrace such “speculative” scenarios.

“We are very conservative at SETI,” Drake says. “We assume in our searches the existence of only things we ourselves have and know how to make.”

5,000

0 Digital Predigital Digital switch when sutro tower in san Francisco converted to digital broadcasts in 2009, its radiated power dropped by more than half —a sobering sign for setI researchers.

no human-produced light could have been detected at interstellar distances.

“In the ’50s, if you wanted a bright
search light, you’d go to GE,” Horowitz
says; the brightest light came from bulbs.
“We couldn’t have predicted the laser.”
Today, powerful lasers can create light
pulses that would outshine their nearest
stars for a billionth of a second. Astrono-
mers observing a momentary burst of
extra light from a distant star could infer
that it came from ET, since most light
from natural sources lasts much longer.

Though such searches are ongoing, Horowitz says optical SETI programs should really look at infrared frequencies, just lower than those of visible light.

“Stars are darker in the infrared and lasers are brighter and the smog goes away,” Horowitz says. Infrared allows astronomers to see into the galactic center, where dust scatters visible light.

For the most part, infrared channels have been off-limits, but technologies from other fields may soon make these searches possible. The communications industry, for example, has developed detectors sensitive enough to spot just a few photons of high-frequency infrared light. And solid-state photodetectors are sensitive at all infrared wavelengths.

Other scientists, and SETI enthusiasts, have proposed hunting in different electromagnetic realms — like gamma rays. Spacecraft that rely on nuclear fusion

Detectable and recognizable

There are people, however, who try to imagine what life could be like thousands of years from now. They’re called science fiction writers, and in their worlds a roving researcher can travel the galaxy, interstellar civilizations can chitchat via music and light shows and, yes, antimatter-matter annihilation can fuel the Enterprise.

SETI researchers, some say, should also contemplate what technologies supersmart aliens might possess and seek out the corresponding signals. In a paper posted at arXiv.org in 2008, John Learned of the University of Hawaii at Manoa suggested that ET could be sending beams of neutrinos Earth’s way. These elementary particles travel close to the speed of light and pass through ordinary matter undisturbed. Energy requirements for such a beam make that scenario seem implausible, but not necessarily impossible.

Detectors currently under construc-
tion—such as IceCube at the South
Pole — could spot unexpected stray neu-
trinos. If a few with the same energy came
from the same direction, astronomers
would know something screwy was up.

Unheard channels major radio searches for extraterrestrial intelligence conducted in the past 50 years have covered just a small portion of possible radio frequencies, mostly focusing on the range between 1 and 3 gigahertz. ongoing and future searches conducted with the Allen telescope Array will cover more channels by simultaneously searching the 0.5 to 11 gigahertz range. researchers also hope to scan more sky, and improve sensitivity, to search deeper into space. SETI frequency coverage so far