Earth calling: A short history of radio messages to ET

The human race first deliberately advertised its existence on the outer panels of space probes, some of which were engraved with codes and images containing information about itself. These immediately prompted arguments about how much we should give away about ourselves.

However, if we really want to break the ice with our cosmic neighbours, it will probably be by sending messages that travel at the speed of light, not at the speed of a Pioneer probe.

A lot of effort has gone into some of the messages, with some researchers even developing an artificial language called Lincos – which so far has not been used in any actual messages.

As part of our special feature marking the 50th anniversary of the search for extraterrestrial life, we round up humanity's radio messages to the stars.

1974: Arecibo message

The first message to be transmitted in the hope of contacting an alien civilisation was quite short, containing just 1679 "bits" of information. This figure was used deliberately: it is the product of two prime numbers, 23 and 73, and if the message is displayed as a 23-by-73 grid it shows a series of simple pictures.

The message was transmitted by the Arecibo radio telescope. It was sent, just once, to the globular cluster M13, where it should arrive in the year 26,974.

1986: Poetica Vaginal

Joe Davis is an artist and a research affiliate at Massachusetts Institute of Technology. In the mid-1980s, he became concerned that no image of humans had been sent into space representing the details of human genitals or reproduction.

So he led a project to transmit the sounds of vaginal contractions towards neighbouring star systems. To do so, he recorded the vaginal contractions of ballet dancers.

The messages were to be sent from MIT's Millstone Hill Radar to Epsilon Eridani, Tau Ceti and two other stars. However, only a few minutes of footage was transmitted before the US air force, which had jurisdiction over the facility, shut the project down.

Nevertheless, the vaginal sounds that were sent will have reached Epsilon Eridani in 1996 and Tau Ceti in 1998. It is unclear what sort of reply we should expect.

1999: Cosmic Call 1

The Cosmic Call messages used the Interstellar Rosetta Stone developed by researchers Yvan Dutil and Stéphane Dumas (PDF). It was based on mathematical and scientific concepts that are thought to be universal, in the hope that any alien who intercepted the messages would understand them. It was followed by short text messages.

The messages were sent using the RT-70 Radio Astronomical Telescope in the Ukraine.

2001: Teen-Age Message

Alexander Zaitsev, a radio engineer at the Russian Academy of Sciences in Moscow and part of the team behind the Cosmic Call messages, was also responsible for this endeavour, in which a group of Russian teenagers sent a message into space.

It used the same transmitter as the Cosmic Call messages, but included analogue information, most notably a concert of electronic music played on the once-revolutionary instrument called the theremin.

The message was sent to six stars, including 47 Ursae Majoris, the first star to be found to have a solar system similar to ours, where any inhabitants will be able to listen to the concert in 2047.

2003: Cosmic Call 2

Four years after it was first transmitted, the Interstellar Rosetta Stone was sent out again, to another five stars. This time, the message included photos and other multimedia files.

Both sets of messages were funded by a company called Team Encounter, which also planned to launch a spacecraft equipped with a solar sail. This would have carried a payload of hair samples, photographs and other items into deep space. However, the company seems to have folded, and the launch never took place.

2005: Craigslist

For the first time, a website was beamed into space. The website in question was the classified listings service Craigslist.

The site was transmitted by a company called the Deep Space Communications Network, which specialises in beaming messages from members of the public into space. It sends its messages into open space, rather than to specific stars, so it is unlikely anybody will pick them up.

2008: Across the Universe

The Beatles song Across the Universe was sent out by NASA in February 2008, to commemorate the 50th anniversary of the agency's founding.

The message was aimed at Polaris, the Pole Star, and should arrive there in 2439. However, Zaitsev criticised the message, noting defects in the method of transmission and also that Polaris is a supergiant star that probably cannot support life.

2008: A Message from Earth

Not content with two Cosmic Calls and a Teen-Age Message, Zaitsev set up a new project called A Message from Earth. This sent out 501 messages selected by a competition on the social networking site Bebo.

As well as half a million members of the public, various celebrities suggested messages, including The X-Files actress Gillian Anderson and the pop band McFly. All these people are now effectively ambassadors for the human race.

The entire capsule was transmitted, again using the RT-70 Radio Astronomical Telescope, towards the planet Gliese 581c, which is so Earth-like it could have liquid water on its surface. The message should arrive in 2028.

2008: Doritos advert

It was a busy year for any extraterrestrial eavesdroppers. In June, radars in the Arctic circle spent 6 hours broadcasting an advert for Doritos into space. The research institute involved, EISCAT, was apparently paid for its efforts by Doritos, hopefully staving off a funding crisis.

Once again, the star 47 Ursae Majoris was chosen as the target of the message.

Later that year, in a second act of intragalactic spamming, the sci-fi movie The Day the Earth Stood Still was beamed towards Alpha Centauri.

2009: Hello from Earth

Last August, Cosmos magazine collected goodwill messages from members of the public and chose the best ones for inclusion in a message called Hello from Earth.

It was sent from the Canberra Deep Space Communication Complex in Australia to the planet Gliese 581d, which is one of the wettest and lightest extrasolar planets known to exist. As the name suggests, it is in the same system as Gliese 581c, which was the recipient of A Message from Earth. The message should arrive in 2029.

2009: RuBisCo message

Artist Joe Davis, who we met previously when he sent recordings of vaginal contractions to nearby stars, returned to the fray on the 25th anniversary of the original Arecibo message.

This time he was a little less racy, transmitting the genetic code for the plant enzyme RuBisCo, which is essential for photosynthesis. RuBisCo is the most abundant protein on Earth, largely because it is so slow and inefficient, so it is certainly representative of life on Earth.

Unlike Poetica Vaginal, this transmission went fairly smoothly – though Davis did have to use his iPhone to get the data into the radio telescope.