IN OCTOBER, NASA’s Europa Clipper spacecraft is due to start its journey to explore Jupiter’s ice-encrusted moon Europa (imagined above in illustration).

NASA asked the scientific organisation that I lead, METI International, to draw on our expertise at attempting to contact extraterrestrial intelligence and help craft a symbolic missive engraved on a tantalum plate attached to the spacecraft – greetings from one water world to another.

We helped create two parts of the message. First, we collected a globally representative sample of audio recordings of the word for water in 103 languages, showing each as a waveform on the outward-facing side of the panel (shown above) that protects sensitive scientific instruments.

On the other, inward-facing side (shown below), we designed the scientific part of the message. This describes water in terms of the “water hole”, the band of frequencies between the hydrogen and hydroxyl (which combine to form water) emission lines in the radio spectrum where many early searches for intelligence beyond Earth were conducted.

Other parts of the interior message include: the Drake equation, which estimates the number of extraterrestrial civilisations in our galaxy; a microchip with the names of 2.6 million endorsers, to be added closer to launch; and US poet laureate poem to Europa, which ends: “O second moon, we, too, are made / of water, of vast and beckoning seas… / of a need to call out through the dark.” The Europa Clipper is due to enter Jupiter’s orbit in April 2030.

, president of METI International

Click here to see images sent into space on NASA’s twin Voyager probes

For nearly 50 years, the Search for Extraterrestrial Intelligence (SETI) has scanned the heavens with radio telescopes for signs of alien technology. At the same time, scientists have painstakingly crafted messages to send in reply. When NASA launched its Voyager missions in 1977, for example, both spacecraft carried audio recordings depicting the diversity of life and culture on Earth (see gallery).

But never have those messages truly represented all of humanity. On 15 May that will change as the SETI Institute launches a . Though there are currently no plans to transmit these messages into space, the project aims to foster a global discussion about whether we should send more than symbolic messages to the stars, and if so, what we should say.

The standard wisdom in interstellar diplomacy is to avoid controversy – a sometimes elusive goal. In the early 1970s, NASA attached plaques to two Pioneer spacecraft etched with basic mathematics, science and line drawings of a man and woman (see image at right). Some complained the space agency was sending “smut into space”, with the naked figures revealing more than they deemed proper for a first encounter.

Other messages have escaped such criticism. One from the Arecibo Observatory in Puerto Rico depicts the human form in so few pixels that its sex is not clear. The Voyager recordings excluded war, poverty and disease.

However, a comprehensive message to the stars should not shrink from the details. Might not an advanced extraterrestrial species, savvy in the ways of intelligent being, notice that something was missing from our description of ourselves? An acknowledgment of our flaws and frailties seems a more honest approach than sending a sanitised, one-sided story. Honesty is a good starting point for a conversation that could last for generations.

If we continue to dodge controversy, we risk sending messages that are both brief and boring. We sometimes clash in our beliefs and customs; we disagree over matters of taste and morality. In no small part this diversity of perspectives is what characterises us as a species. And it may just make us intriguing enough to the inhabitants of other worlds to elicit a reply.

Click here to see images sent into space on NASA’s twin Voyager probes

is director of interstellar message composition at the SETI Institute in Mountain View, California