Don't Phone E.T., Just Send a Text Message

Though astronomers have been listening for radio transmissions from extraterrestrial civilizations for 50 years, there have been just a few attempts at transmitting a message to any inquiring alien minds that might dwell among the stars.

The most widely popularized nocturnal transmission was a message commemorating the reopening of the newly resurfaced Arecibo radio telescope. The interstellar greeting was broadcast on November 16, 1974, and the SETI Institute folks just celebrated the message’s 35^th anniversary.

The interstellar “hello,”  crafted by Carl Sagan and Frank Drake, was aimed at the globular star cluster M13 in the constellation Hercules, and won’t arrive for another 25,000 years. (Subsequent Hubble Space Telescope observations of the globular cluster 47 Tucane failed to find any evidence for planets in these ancient stellar beehives, which are largely deficient in the heavier elements needed to make planets and people.)

The 1000-kilowatt transmission consists of a string of 1679 binary digits. The value 1679 was chosen because it is a product of two prime numbers. The assumption is that smart aliens would arrange it into 23 rows by 73 columns – assuming they like portrait instead of landscape layouts. This forms a mosaic image when the “1’s” are filed in. The pictogram shows the solar system, a Gumby-like human figure, DNA's helical structure, and binary values for the atomic weights of some basic Earth biochemistry, among other graphics.

These attempts so far all must assume that the receiving alien culture has an understanding of science and math. But the transmissions have never been tested for decipherability according to California Institute of Technology geoscientist Michael Busch and Stanford University physicist Rachel Reddick.

They recently published a study where Busch developed a code scheme for an interstellar message, and Reddick deciphered it in 12 hours flat, without any clues. They then gave the message to five undergraduates, who each independently spent no more than an hour attempting to decode it without any pattern-recognition software.  Three of the students correctly identified the basic “informational block” architecture of the message.

Busch kept the message simple, to only 75 kilobytes. It is essentially a string of mathematical statements that establish some fundamental math, physics, and describe the solar system’s physical parameters. This has much less ambiguity than pictograms say the researchers, and a higher information density per transmitted kilobyte.

To reliably decrypt such a message the alien astronomers only need a common knowledge of stellar astronomy, and the physics and mathematics required to build a radio telescope, say the researchers. Almost all SETI-at-home type data-analysis programs would detect the signal.

Here’s a detection scenario based by Busch’s and Reddick’s work:

Astronomers of an extraterrestrial technological civilization identify an interstellar beacon. They pinpoint the sun as the likely source of the transmission. Data archives are searched and telescopes are aimed at our sun to measure its mass, composition and above all, age. The aliens conclude that the sun is old enough to allow for several billion years of biological evolution. Their powerful space telescopes, outfitted with coronagraphs, seek out any planets in the sun’s habitable zone. Or perhaps Earth had already been identified as an interesting target and alien SETI astronomers were monitoring it.

The extraterrestrials do not need supercomputers for decoding the signal because of the small amount of data in the message.  Actually the aliens' equivalent of a paper and pencil will suffice. E.T. scientists quickly recognize that the binary strings ‘00000000’ and ‘00010000’ occur in the message far more frequently than other strings. These strings are interpreted as separating individual blocks of code from each other.

Once plotted with these delimiters (the equivalent of commas or colons in a sentence), the blocks of statements look like:

         ( 10000000 01000001 10000000 )

         ( 10000003 01000001 10000003 )

         ( 10022133 01000001 10022133 )

         ( 10000000 01000001 20000000 ) 

         ( 10000001 01000100 20000001 ) 

         ( 10000001 01000100 10000000 )

         ( 10031242 01000100 10031243 )

After working their way though a binary encoded tutorial on the simple mathematics and units of measurement employed in the message, the alien scientists sort though a Cliff Notes version of our scientific knowledge.

Values are given for the mass, temperature, diameter, and elemental composition of the sun. Alien astronomers check this against their own solar observations and are reassured they’ve got the decoding correct.

The message next provides the masses, diameters, temperatures of the solar system’s planets, and their orbital periods and heliocentric distances. The composition of the third planet from the sun is described as having an excess of oxygen. The aliens match the curious planet’s orbital period to their Doppler data and conclude this is the source of the SETI transmission. (Though if they aren’t oxygen breathing creatures, the aliens might wonder how life survives in such an explosive, toxic, non-reducing atmosphere.)

I would expect that if extraterrestrials thought along similar communication lines and “texted” us their message would include a number of astronomical values which are truly universal: the expansion rate of the universe, the matte /energy density of the universe, the gravitational constant, and the equation of state for dark energy. And, how about galactic coordinates for other know civilizations?

Though there are no plans to transmit such a message, this experiment expands our ideas as to what kind of information content we might ultimately receive from E.T. (And probably not blueprints for a subspace matter transmitter, as imagined in Carl Sagan’s novel Contact.)

But finally, how do you wrap up such a message and invite the alien culture to text back to us?

How about:

::-X