Radio Bubble: alien couch potatoes? It's possible, thanks to escaping TV and radio signals

Natural History, Nov, 2001 by Neil deGrasse Tyson

A better way to communicate is to send a high-intensity radio signal to a busy place in the galaxy, such as a star cluster. This was first done in 1974 when, as a test of the concept, the Arecibo telescope was used in reverse--to transmit rather than to receive. It sent the first radio-wave signals of our own choosing out to space. That message is now headed in the direction of the spectacular globular star cluster known as M13, among the stars tracing the constellation Hercules. The message contains in digital form some of what appeared on the Pioneer and Voyager plaques. In 25,000 years, when the signal arrives, those intelligent aliens living on M13's planets will know how smart we are.

But there are two problems: The M 13 cluster has such a meager quantity of heavy elements (the raw materials of planets) that planets are probably rare among its stars. Furthermore, the globular cluster is so chock-full--it has about half a million tightly packed stars--that any planets it does have would have unstable orbits. A planet's gravitational allegiance to its host star would be challenged every time the star passes through the cluster's center.

In any case, the leading edge of our "on purpose" radio signals (which form directed radio cones instead of bubbles) is now twenty-seven light-years away. If intercepted, it may mend the image of us that the aliens would have deduced from our television shows. But this will happen only if they can somehow determine which signals come closer to what our cosmic reputation deserves to be.

Astrophysicist Neil deGrasse Tyson is the Frederick P. Rose Director of New York City's Hayden Planetarium and a visiting research scientist at Princeton University.