SETI@Arecibo: Bigger is Better

March 12, 2001

by Seth Shostak - Senior Astronomer

Project Phoenix is back at Arecibo, checking out nearby stars for signs of intelligent life. Astronomer Seth Shostak is reporting from the observatory once again, and will be home to his Arecibo Diaries. This is the second installment.

"Arecibo interface is up and running," I bark from a computer console.

"OK, I’m taking control…" Jill Tarter replies flatly. "Check the IF levels, would you?"

It’s 6:00 p.m., and Project Phoenix is once more checking out nearby star systems, listening for a radio tone that would betray an alien society. Every night, from 6:00 p.m. to 6:00 a.m., we take over the world’s largest antenna and aim it at Sun-like stars.

"Truly amazing," notes Robert Ackermann, a software scientist at the SETI Institute, as he peers down at the telescope’s imposing aluminum dish. "This is some weird hybrid of locomotive and battleship. Look at all the steel. It’s hard to believe you can point this beast to within 6 seconds of arc."

That’s one-six hundredth of a degree – roughly the size of a lunar crater seen from Earth – or if you prefer, like hitting a dime from 350 yards. Not bad for an instrument whose moving parts weigh in at 340 tons.

Rob is here with Gerry Harp, another software scientist. Their day jobs, back at the institute, are to construct the systems that will drive and point the new Allen Telescope Array – an instrument that, when completed in 2005, will be used 24-seven for SETI observations. This is their first trip to Arecibo, and they’re still gasping at the size of the antenna. "It’s really hard to appreciate how big this thing is," Gerry says. "I don’t want to sound like a teenager, but let’s face it -- it’s awesome."

"You might get lucky and find the aliens" signal your first night out," I venture. "But it"s not this one."

"Awesomeness" has its rewards, because when SETI is your bread and butter, bigger is really better. The bottom line of using an awesome antenna is that Project Phoenix can detect signals as weak as 0.8 Jansky. Now if you happen to be a radio astronomer, that number may mean something to you. If not, let me put it this way: imagine a tiny, downy, duck feather dropped from your hand onto the floor. When that fallen feather slams into the linoleum, the energy released is 100 trillion times greater than that collected by the entire Arecibo dish during a five-minute observation of a 0.8-Jansky signal.

It boils down to this (something noted in my last diary piece): radio technology is good – which is to say, it’s remarkably sensitive. That’s why it makes sense to try and find evidence of aliens from a distance of 100 light-years (580 trillion miles; 933.4 trillion kilometers) or more. It takes an enormous amount of energy to travel such distances. But a transmitter no more powerful than your favorite TV station could easily bridge the gap with a fast-moving signal.

We’re observing star 4791 in our list. It’s a G0 star (i.e., fairly similar to the Sun), 111 light-years from downtown Arecibo. Typical. We’ve been at it for 25 minutes when Ackermann and Harp begin chattering. "Hey, we’ve got a hit!"

A signal found in Arecibo has been given the thumbs-up by its sibling ‘scope in Jodrell Bank, England. It might be extraterrestrial. The Phoenix software calmly stops its regular observing routine and points the Arecibo antenna away from 4791. The idea is to see if the suspicious signal goes away or not.

Within a few minutes we know the answer. The signal’s still there, marked by a thin, gently curved line on the screen. It’s some sort of low-orbit satellite whose signal is bouncing around the telescope structure and looking (at least for a few minutes) like ET’s call. Jill and I are sympathetic to the newbies’ disappointment. "You might get lucky and find the aliens’ signal your first night out," I venture. "But it’s not this one."

The evening wears on. Around midnight, we scramble to point Arecibo at the Moon, and look for a test signal bounced off it. It takes sweat, frustration and 20 minutes of pounding on keyboards, but finally we find the 10-watt signal that the SETI League in New Jersey has sent skyward for our benefit. It’s weaker than I had expected, but there’s no doubt about it – the bounced signal is definitely there. This technique may soon be an effective scheme for checking our system.

The Moon drops to the west, and we’re onto a new star system. "Like watching grass grow," says Harp, as he fills in the logbook. Yes, perhaps. Growing grass. But one of these nights a bloom could appear.