In 1974, humans broadcast the first message targeted at extraterrestrial life using the Arecibo radio telescope in Puerto Rico. The message, which was aimed at the globular star cluster M13 located 25,000 light years away, consisted of binary digits that encoded information about our DNA, as well as graphics of a human, our Solar System, and the Arecibo telescope. Since then, humans have sent three other messages to nearby stars and planets (20-69 light-years away). These messages have become more complex and anthropocentric, with music, photographs, and drawings submitted by the public.
Now a team of scientists, Dimitra Atri from the University of Kansas, Julia DeMarines from the International Space University in France, and Jacob Haqq-Misra from Pennsylvania State University, has proposed that future attempts of messaging to extraterrestrial intelligence (METI) should follow a standard protocol to maximize communication effectiveness. They think that some of the content of past METI broadcasts, which contain sights and sounds, would likely go unnoticed by extraterrestrials who do not have visual or auditory perception (like some organisms on Earth). Instead, the researchers argue that short, simple messages with minimal anthropocentrism, and which rely on simple physical or mathematical language, have the best chance of success.
In their study, which will be published in a future issue of Space Policy, the researchers say that a METI protocol should provide constraints and guidelines for factors such as signal encoding, message length, information content, anthropocentrism, transmission method, and transmission periodicity. Currently, there are three antennas that have the capability of transmitting messages to planets anywhere in our galaxy; these telescopes are located in Arecibo, Puerto Rico; Goldstone, California, US; and Evpatoria, Crimea, Ukraine.