Some researchers want to use big radio dishes like the 305-meter Arecibo Observatory in Puerto Rico to announce our presence to intelligent aliens.

Is it time to take the search for intelligent aliens to the next level?

For more than half a century, scientists have been scanning the heavens for signals generated by intelligent alien life. They haven't found anything conclusive yet, so some researchers are advocating adding an element called "active SETI" (search for extraterrestrial intelligence) — not just listening, but also beaming out transmissions of our own designed to catch aliens' eyes.

Active SETI "may just be the approach that lets us make contact with life beyond Earth," Douglas Vakoch, director of interstellar message composition at the SETI Institute in Mountain View, California, said earlier this month during a panel discussion at the annual meeting of the American Association for the Advancement of Science (AAAS) in San Jose. [13 Ways to Hunt Intelligent Alien Life]

"Whenever any of the planetary radar folks are doing their asteroid studies, and they have an extra half an hour before or after, there's always a target star readily available that they can shift to without a lot of extra slough time," he said.

The content of any potential active SETI message is a subject of considerable debate. If it were up to astronomer Seth Shostak, Vakoch's SETI Institute colleague, we'd beam the entire Internet out into space.

"It's like sending a lot of hieroglyphics to the 19th century — they [aliens] can figure it out based on the redundancy," Shostak said during the AAAS discussion. "So, I think in terms of messages, we should send everything."

While active SETI could help make humanity's presence known to extrasolar civilizations, the strategy could also aid the more traditional "passive" search for alien intelligence, Shostak added.

"If you're going to run SETI experiments, where you're trying to listen for a putative alien broadcast, it may be very instructive to have to construct a transmitting project," he said. "Because now, you walk a mile in the Klingons' shoes, assuming they have them."

Cause for concern?

But active SETI is a controversial topic. Humanity has been a truly technological civilization for only a few generations; we're less than 60 years removed from launching our first satellite to Earth orbit, for example. So the chances are that any extraterrestrials who pick up our signals would be far more advanced than we are. [The Search for Intelligent Life: 4 Key Questions (Video)]

This likelihood makes some researchers nervous, including famed theoretical physicist Stephen Hawking.

"Such advanced aliens would perhaps become nomads, looking to conquer and colonize whatever planets they could reach," Hawking said in 2010 on an episode of "Into the Universe with Stephen Hawking," a TV show that aired on the Discovery Channel. "If so, it makes sense for them to exploit each new planet for material to build more spaceships so they could move on. Who knows what the limits would be?"

Astrophysicist and science fiction author David Brin voiced similar concerns during the AAAS event, saying there's no reason to assume that intelligent aliens would be altruistic.

"This is an area in which discussion is called for," Brin said. "What are the motivations of species that they might carry with them into their advanced forms, that might color their cultures?"

Brin stressed that active SETI shouldn't be done in a piecemeal, ad hoc fashion by small groups of astronomers.

"This is something that should be discussed worldwide, and it should involve our peers in many other specialties, such as history," he said. "The historians would tell us, 'Well, gee, we have some examples of first-contact scenarios between advanced technological civilizations and not-so-advanced technological civilizations.' Gee, how did all of those turn out? Even when they were handled with goodwill, there was still pain."

Out there already

Vakoch and Shostak agreed that international discussion and cooperation are desirable. But Shostak said that achieving any kind of consensus on the topic of active SETI may be difficult. For example, what if polling reveals that 60 percent of people on Earth are in favor of the strategy, while 40 percent are opposed?

"Do we then have license to go ahead and transmit?" Shostak said. "That's the problem, I think, with this whole 'let's have some international discussion' [idea], because I don't know what the decision metric is."

Vakoch and Shostak also said that active SETI isn't as big a leap as it may seem at first glance: Our civilization has been beaming signals out into the universe unintentionally for a century, since the radio was invented.

"The reality is that any civilization that has the ability to travel between the stars can already pick up our accidental radio and TV leakage," Vakoch said. "A civilization just 200 to 300 years more advanced than we are could pick up our leakage radiation at a distance of several hundred light-years. So there are no increased dangers of an alien invasion through active SETI."

But Brin disputed this assertion, saying the so-called "barn door excuse" is a myth.

"It is very difficult for advanced civilizations to have picked us up at our noisiest in the 1980s, when we had all these military radars and these big television antennas," he said.

Shostak countered that a fear of alien invasion, if taken too far, could hamper humanity's expansion throughout the solar system, an effort that will probably require the use of high-powered transmissions between farflung outposts.

"Do you want to hamstring all that activity — not for the weekend, not just shut down the radars next week, or active SETI this year, but shut down humanity forever?" Shostak said. "That's a price I'm not willing to pay."

So the discussion and debate continues — and may continue for quite some time.

"This is the only really important scientific field without any subject matter," Brin said. "It's an area in which opinion rules, and everybody has a very fierce opinion."

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