Posted by: Kash Farooq | April 7, 2013

Frank Drake and the Arecibo Message

In 1974, a specially encoded message (that become to be known as the Arecibo Message) was broadcast into space towards the globular cluster M13 in the constellation of Hercules:

Globular Cluster M13 in Hercules

Globular Cluster M13 in Hercules. Image acquisition by Jim Misti, image processing by Robert Gendler.

The message was broadcast by Frank Drake from the enormous (you can see road and a car in the foreground) Arecibo Observatory radio telescope in Puerto Rico:

The Arecibo Observatory

The Arecibo Observatory. Image courtesy of the NAIC, a facility of the NSF.

The message was intentionally sent to broadcast Earth’s existence to any alien civilisation that might be listening. No permission was obtained from the rest of the planet. Frank Drake just decided to do it. Sir Martin Ryle (who was the Astronomer Royal at the time) wrote to Drake questioning the wisdom of this act. However, even if some hostile civilization received (and understood) the message, we don’t need to be overly concerned – M13 is 50000 light years away.

Just 1679 bits of information were transmitted. Compared to today’s data quantities, this is a tiny amount of data. Even so, in 1679 bits, an impressive amount of information was broadcast. The message was carefully designed by Frank Drake and Carl Sagan to provide as much information as possible in this small data packet.

Why was the message encoded in 1679 bits? 1679 is the product of two prime numbers (23 and 73), and mathematics is the only common language humans could possibly have with an alien civilization. The intention was that the receiver would convert the incoming 1679 binary bits into a 23 by 73 rectangle, colouring in the ‘ones’ and leaving the ‘zeros’. This would result in this:

The Arecibo Message

The Arecibo Message

The colours have been added to distinguish between the different areas of the message.

Message Part 1 – The Numbers 1 to 10

The white dots at the top of the message represent the numbers 1 to 10, in binary. Each dot in the bottom row is ignored (it just signals the start of number). Hence we have 1, 10 (decimal 2), 11 (decimal 3), etc.

Message Part 2 – Elements found in DNA

The next section (purple) represents the atomic numbers of the elements found in DNA: hydrogen, carbon, nitrogen, oxygen, phosphorous. Again, ignore the bottom row – so the first column has one dot in it, signifying the atomic number of hydrogen.

Message Part 3 – Nucleotides

The green section follows on from the elements presented in part 2 and shows the molecular formula of each nucleotide – e.g. the top left collection of dots is deoxyribose C5OH7 and needs to be read as (ignoring the bottom row again): 7 atoms of hydrogen, 5 atoms of carbon, 0 atoms of nitrogen, 1 atom of oxygen, and 0 atoms of phosphorus.

The next symbol is adenine (C5H4N5), then Thymine (C5H5N2O2), etc.

Message Part 4 –  The DNA Double Helix

The blue curved lines represent the DNA double helix, with the white vertical line representing the number of nucleotides in DNA.

Message Part 5 – Humans

This red symbol clearly represents a human. Apart from the obvious shape, there is also information to left and the right of the red figure.

The white bits on the left represent the binary number 1110.

Note: this image from Wikimedia Commons has the number on the left – I’ve seen other images with the number on the right. It makes more sense on the right, as then it would actually read 1110.

1110 is 14 in decimal. The message was broadcast at frequency 2380 Hz, which is equivalent to the wavelength 12.6 cm. 14 x 12.6 cm = 176.4 cm. This is the average height of a human.

The white bits on the right of the red human form represent the population of Earth at the time the message was broadcast – which was just over 4.25 billion in 1974.

Message Part 6 –  The Solar System

The yellow dots represent the Solar System, with the large Sun on the left and Earth slightly raised to show that “We Are Here”. Also, the human form is directly above the raised dot, again showing where we live.

Message Part 7 – The Arecibo Observatory

Finally, the bottom image represents the Arecibo Observatory dish that broadcast the message with the dots at the bottom representing the diameter of the dish.

What happens when you give this message to a human?

As you can see, Sagan and Drake managed to cram a lot of information into such a small number of bits. Whether an alien civilization would be able to decode the message or not is another matter. Drake presented the binary bits to some of his colleagues – only some of them were able to partially decode the message; no one was able to fully decode it.


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