Arecibo Observatory Used M13 to Target Extra-terrestrials
Image Credit: Arecibo Observatory (Cornell, NAIC)
Radio Message Sent to M13 in 1973
Image Credit: F. Drake (UCSC) et al., Arecibo Observatory
Globular cluster M13 was chosen as a target for one of the first radio messages addressed to possible extra-terrestrials. This message was sent by the giant radio telescope of the Arecibo Observatory in Puerto Rico, at a ceremony to mark the remodeling of the telescope on November 16, 1973.
M13 was a selected because it a large collection of stars that was available in the sky at the time and place of the ceremony. It will take 25,000 years for the message to reach M13 and if any reply were to be received it would take another 25,000 years to reach Earth, a total of 50,000 years. The Arecibo message was more a symbolic event to demonstrate the capabilities of the newly installed equipment than an actual attempt at communication.
In fact, M13 is a very unlikely place to find planets and life. The stars in M13 are very old and consequently contain very little metal since they were formed at a time when basic elements like iron had not yet been forged by other stars. It is therefore unlikely that earthlike planets formed around any of the stars in this cluster.
Dr. Frank Drake, creator of the Drake equation, wrote the message, with help from Carl Sagan, among others. It consisted of 1679 bits, to be arranged in 73 rows by 23 columns (those both being prime numbers). It graphically described a binary number sequence, hydrocarbon chemistry, DNA, the human figure (including a height scale), our solar system, and the Arecibo dish transmitting the signal.