Dear Aliens, Read This

If you could send a message into outer space, to be read by alien life forms, what would you say?  How would you say it?

In the mid-1970s, a group of astronomers and astrophysicists not only tackled this exact question, but they also acted on it, sending a message into space hurtling toward the Hercules constellation 25,000 light years away.  What they sent is called the Arecibo Message: 1,679 binary characters as seen, below.

The message was sent as frequency modulated radio waves, yielding two types (to us, ones and zeroes).  This was done to mark the completion of the Arecibo Radio Telescope which opened in late 1974.  The telescope, pointed at the stars, “listens” for radio waves from outer space for similar messages.

But in this case, we Earthlings were sending, not receiving.  The message has seven parts.    (The colors have been added afterward to help us differentiate the parts of the message; the message itself doesn’t contain that information.)  First, in white the numbers 1 to 10; then purple, the elemental components of DNA; in green, the nucleotides which make up DNA; below, in white and blue, a double helix; below that, three images representing “humanity;” in yellow, the Solar System; and then finally, in purple (plus the blue and white below it), the telescope.  The explanation of each?  Wikipedia does a great job with it.

As a string of 1,679 1s and 0s, the team which put together the message hopes that any alien life form which encounters this literal shot in the dark knows about math.  The number 1,679 was not chosen accidentally.  It is a “semiprime number” — a number which is a product of two prime numbers; in this case, 73 and 27.  Therefore, there are only two ways to arrange the string (other than as one row): 23 rows by 73 columns; or, as intended, 73 rows by 23 columns.

Of course, this is likely moot.  By time the message reaches its intended target, civilization as we know it will be a historical footnote.


Bonus fact: The Arecibo Message is already out of date.  Its representation of the Solar System includes Pluto, which is no longer a planet.

From the Archive: The Earth’s Bulls-Eye: In case the aliens want to reply in “person,” here’s a good landing spot.

Related: You can buy a t-shirt with the Arencibo Message on it.  It’s a bit over-priced (to say the least) but imagine how much it may be worth in 50,000 years.