Could Aliens Be Sending Us Laser Signals?

Over a decade ago SETI pioneer Jill Tarter and I had a dinner discussion about the protocol procedures for announcing to the world the first detection of a signal broadcast from an extraterrestrial civilization.

I expressed relief that I would never have to worry about publicizing such a discovery from Hubble Space Telescope. “Hold on Ray,” Jill said, “you never know, Hubble might conceivably pick up a signal that other telescopes can’t detect.”

Oh, my worst nightmare! Imagine keeping that information under a news release embargo!

Now, some readers will scratch their heads at this because SETI has been popularized in the 1997 movie Contact where actress Jodie Foster “listens” for radio signals from E.T. with the huge radio telescope array near Socorro, New Mexico.

But another communication strategy that aliens might use instead of radio signals is to send brief and intense bursts of laser light across the galaxy – sort of like a signal lamp between two ships. Some space telescopes would be ideally suited to pluck out such a signal from the sky background.

Why laser beams instead of radio transmitters? A directed beam across interstellar space would be unmistakable from the stellar background and could penetrate thousands of light-years. With each pulse of energy a signal from a big enough laser optics system could appear 1 million times brighter that the transmitting planet’s parent star. The thought is that an alien society would use an agile laser-transmitter to “paint” nearby target sunlike stars with a “searchlight beam.”

An advanced alien civilization would not have to bust its annual GNP to construct a super-laser. Ideally, they would build a telescopic mirror the width of 10 football fields. They’d shine a laser into it that is capable of pumping out a blinding 1 quadrillion watts of energy in brief bursts (just such a laser is already in operation at the University of Texas).

Now, a petawatt is 1,200 times the entire electrical generating capacity of the United States -- but the shots last for less than a trillionth of a second each. The laser could pulse at one blast per second or so.

The pulse sequence might have a mathematical pattern embedded in it. This could yield a complex and lengthy message, or simply repeat a shorter transmission for redundancy (so long as it does not decode into those sappy musical tones from the 1977 film Close Encounters of the Third Kind)

There have been numerous optical SETI (OSETI) searches with ground-based telescopes, going all the way back to the early 1970s. Ironically, the newly launched NASA Kepler space observatory might be capable of stumbling across just such a signal too. It has the light sensitivity, photometric precision, time resolution, and sample size (170,000 stars) to do, serendipitously, an unofficial (and unsanctioned) OSETI experiment from a space platform.

In addition to doing a census of stars with Earthlike worlds, it is not entirely impossible – however remote – that the observatory could stumble upon an artificial laser transmission. In fact SETI researcher Steve Kilston has gone so far as to assert that if Kepler doesn’t get laser-zapped, the result would statistically reduce the estimated number of actively laser-transmitting civilizations in the Milky Way Galaxy to less than one million (and of course it could also be "zero").

A variety of other space telescopes could be similarly adept at coming across an OSETI signal. The European Space Agency’s Gaia observatory (2011 launch) will map the position and velocities of one billion stars in our galaxy. Its onboard multi-color photometer is capable of serendipitous OSETI detections.

A wildly ambitious, spendthrift super-civilization – a million years more technically evolved that us -- might build a moon-sized laser mirror. They would tap a fraction of their star’s energy just to power a godzillion-watt laser capable of transmitting an intergalactic beacon across millions of light-years.

Perhaps a future space telescope might intercept such a signal. The question is, how long will it take the researchers to shake off their amazement and disbelief, and dare tell their colleagues?

Photo Credit: University of Texas, Adam Contos/Ball Aerospace