When we learn of the existence of intelligent life beyond Earth, the first question we are likely to ask is, "How can we communicate?" As we approach the 50th anniversary of the 1974 Arecibo message - humanity's first attempt to send a message capable of being understood by extraterrestrial intelligence - this question is more relevant than ever. Advances in remote sensing technology have shown that the vast majority of stars in our galaxy have planets, and that many of these exoplanets are capable of having liquid water on their surface - a necessary condition for life as we know it. The likelihood that at least one of these billions of planets has originated intelligent life seems high enough to spend some time figuring out how to say hello.
In early March, an international team of researchers led by Jonathan Jiang of NASA's Jet Propulsion Laboratory posted a paper on the arXiv.org preprint server detailing a new message design intended for extraterrestrial recipients. The 13-page message, called Beacon to the Galaxy, is intended to be a basic introduction to mathematics, chemistry and biology, drawing heavily on Arecibo's message design and other past attempts to communicate with extraterrestrials. The researchers included a detailed outline of the best time of year to transmit the message and suggested a dense ring of stars near the centre of our galaxy as a promising destination. Importantly, the transmission also includes a specially designed return address to help alien listeners pinpoint our location in the galaxy so they can hopefully start an interstellar conversation.
"The motivation for creating this project was to convey as much information about our society and the human race as possible in a minimal message," says Jiang. "With improvements in digital technology, we can do much better than [Arecibo's message] did in 1974."
Every interstellar message must answer two fundamental questions: what to say and how to say it. Almost all of the messages that humans have sent into space so far start by establishing a common language with a basic lesson in science and mathematics, two topics that are presumably familiar to both us and the aliens. If a civilisation outside our planet is capable of building a radio telescope to receive our message, it probably knows something about physics. The much more difficult question is how to encode these concepts into the message. Human languages are out of the question for obvious reasons, but so are our number systems. Although the concept of numbers is almost universal, the way we represent them as numbers is entirely arbitrary. This is why many attempts, including Lighthouse in the Galaxy, have chosen to frame their writing as a bitmap - a way of using binary code to create a pixel image.
The philosophy of bitmap design for interstellar communication goes back to Arecibo's message. It's a logical approach - on/off, the presence/absence of binary code seems likely to be recognised by any sentient species. But this strategy is not without its flaws. When the pioneer in the search for extraterrestrial intelligence (SETI), Frank Drake, created a prototype Arecibo message, he mailed the binary message to several colleagues, including several Nobel laureates. None of them could understand its contents, and only one guessed that the binary message must have been a bitmap. If some of the smartest humans have trouble understanding this form of message encoding, it is unlikely that aliens are doing any better. Moreover, it is not even clear whether space aliens would be able to see the images contained in the message if they received it.