Quirks & Quarks·Analysis

Famous Arecibo telescope was the first to send a signal to alien civilizations

Bob McDonald's blog: Damage to historic instrument means it will be dismantled

Bob McDonald's blog: Damage to historic instrument means it will be dismantled

The Arecibo Observatory has determined that damage to their massive radio telescope is not safely repairable. (Arecibo Observatory/ The Associated Press)

After almost six decades of cutting-edge research — and having survived hurricanes and earthquakes — the world's most famous radio telescope is to be decommissioned. Part of its legacy is a little known experiment that used the telescope to send a message from Earth to places where there might be other potential civilizations in our galaxy. 

Nestled in the highlands of Puerto Rico, the 305-metre-diameter dish of Aricebo made it the largest radio telescope in the world, unique in its design when it was built in 1963.

Unlike other radio telescopes that are mounted on enormous movable platforms, the Arecibo dish was laid out in the bottom of a natural circular hollow, which allowed it to reach such enormous proportions. Because it remains stationary and points straight up, it uses the rotation of the Earth to scan the skies as the stars pass overhead. 

Sadly, the structure became unsafe after supporting cables holding the 900-tonne instrument platform let go this summer and fall, sending debris crashing through the dish to the ground. The damage makes the huge telescope too dangerous to repair, and so the U.S. National Science Foundation has announced that the facility will be closed and the structure dismantled. 

The Arecibo radio telescope in Puerto Rico. (Seth Shostak/SETI Institute/Associated Press)

During its lifetime, the Arecibo telescope made numerous discoveries, detecting planets in other solar systems, spotting neutron stars and pulsars, and observing molecular clouds in other galaxies.

But in addition to receiving radio signals from the astronomical phenomena in the cosmos, it was also a powerful radio transmitter, able to send out 2.5 megawatt radio beams that could be bounced off asteroids passing close to Earth to get an idea of their shape and orbital motion. 

That transmitting ability was also used to explore one of the most fundamental questions in astronomy: "Is anyone out there?"

In 1974, astronomers Frank Drake and Carl Sagan, from Cornell University, designed a message that encodes crude images of a human being, the DNA molecule, the planets in our solar system and the telescope itself. 

A representation of the digital Arecibo message (Arecibo observatory/US National Science Foundation)

The giant telescope was used to beam the signal across our galaxy to a star cluster called M13  in the constellation Hercules. The cluster contains about 300,000 densely-packed stars, many of which are at least 12 billion years old. In solar systems around these old stars there's certainly been time, if conditions are right, for intelligent civilizations to have potentially evolved.

The beamed message would reach a large number of stars at once increasing the chances of contact — if anyone's listening. 

Of course, no one is expecting an answer to the signal anytime soon because M13 is roughly 25,000 light years away, so the message will take 25,000 years just to get there. Then, if anyone detects it, and if they understand it, and if they feel like answering, it will be another 25,000 years for their signal to reach us.

That's 50,000 years just to say, "Hi, is anyone out there?" and get the reply, "Yes, what do you want?" It clearly demonstrates the difficulties of communicating over astronomical distances, which was Drake's actual reason for the exercise. 

He also developed the Drake Equation, which was meant to calculate the odds of there being other intelligent civilization in a galaxy. He also founded the found the SETI Institute, which is dedicated to the search for signals from other civilizations and used the Arecibo telescope for a time to conduct that search of the heavens — listening for the kind of signal that Aricebo had beamed out in 1974.

An aerial view shows the Five-hundred-meter Aperture Spherical Telescope (FAST) in the remote Pingtang county in southwest China's Guizhou province. (Liu Xu/Xinhua/Associated Press)

Astronomers will mourn the loss of the big dish and will have to move their research to other facilities, including another even larger dish of similar design that recently became operational in China. It's called FAST, which stands for Five- hundred-metre, Aperture, Spherical Telescope. It will take over where Arecibo left off. Perhaps one day another interstellar message will be sent from there.

Who knows, perhaps one day, 50 millennia from now, aliens who have followed our signal to its origin will land in Puerto Rico, look into that hollow in the ground and wonder, who were those people who reached out to say hello?

About the Author

Bob McDonald is the host of CBC Radio's award-winning weekly science program, Quirks & Quarks. He is also a science commentator for CBC News Network and CBC-TV's The National. He has received 12 honorary degrees and is an Officer of the Order of Canada.

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