DRAKE'S EQUATION
The Milky Way galaxy contains over 400 billion stars (and is only one of billions of other galaxies). Could it be that ours is the only planet where life arose? Perhaps. Or maybe life is common, but too often destroys itself as technology becomes too powerful to handle.

But we should also consider that the sheer vastness of space and the great number of stars and planets has given rise to a number of technological civilizations capable of communication.

The Drake Equation gives a means for estimating how many communicating civilizations may be out there. The results can vary widely, depending on the optimism of the numbers you yourself plug in. The equation computes N: the potential number of communicative intelligent civilizations in our galaxy.

It is computed using the following equation...

N = R* x fs x fp x ne x fl x fi x fc x L ...

using the following factors:

R* is the rate of formation of stars in the galaxy

fs is the fraction of stars that are
suitable suns for planetary systems

fp is the fraction of those stars with planets
(thought to be around 1/2)

ne is the number of "earths" per planetary system
-- planets suitable for liquid water

fl is the fraction of those planets where life develops

fi is the fraction of planets with life
where intelligence develops

fc is the fraction of those planets that achieve technology which releases detectable signals into space

L is the lifetime of such communicative civilizations

Depending on the numbers used, the Drake equation can yield wildly differing results. Possibilities range from a few (relatively) short-lived technological civilizations scattered far apart among the stars, never contacting each other before they disappear, to a more probable (considering the vastness of the cosmos) large number of life-bearing planets.

There are over 400 billion stars in our galaxy alone, and it is estimated that approximately 1/2 of all suitable suns have planetary systems of some sort. It is not known how likely it is for life to develop on a suitable planet. Once life does exist, however, it is quite evident from our own evolutionary history that it is quite adaptable and tenacious. The jury is still out, however, on how long species survive once they have developed intelligence and powerful technology.

Contact

The problems of deliberately communicating with an alien intelligence are enormous.

Imagine trying to write a letter to someone the other side of the world who you don't know personally. Imagine that the person might not speak English and that you are not sure what language they do speak. Also, you are not sure of their address or even which country they are in. It's also possible they are not even a person but a tiger or even a dolphin!

The best sort of signal to send into space is perhaps pictorial. It should then be possible to contact other beings and to show them about our civilisation by showing pictures. This is a person. This is our Sun etc. That way it would also be possible to teach our language as well as demonstrating our basic form. To send the message as far as possible, it needs to be as simple as possible, which reduces the possibility of it becoming garbled: it needs to be a binary signal. Where do you start?

Some of the messages that we have sent have both pictures and sounds.

The Voyager Interstellar Recording was attached to both the Voyager 1 and 2 space crafts, which were launched on August 20 and September 5, 1977. The Record is a gold-plated record encased in aluminium. The instructions on how to play the record are engraved on the case.

Included on the record is music from different cultures, greetings in over fifty languages and various animal noises including the songs of the humpback whales. There is also an hour long recording of the electrical activity of a person's body. A cartridge and stylus are included and the recording should last for one billion years.

Pioneers 10 and 11 were launched in 1972 and 1973 respectively and both carry six-by-nine inch gold plaques. Designed by Carl Sagan’s wife, Linda Salzman Sagan, the finished picture shows a nude man with his hand raised in greeting, with a nude woman by his side. Both figures are of average height and their features are a mixture of various racial characteristics. They are stood in front of a scale model of the Pioneer space craft and have a pulsar map to the left. There is also a map of the Sun and planets with the trajectory of the Pioneer from earth.

Pioneer 10 is now 6.6 billion miles away and transmitted as recently as 1998. Pioneer 11 is no longer transmitting.

On November 16, 1974 a message was sent from the Arecibo Observatory in Puerto Rico. It consisted of 1,679 bits. That was the upper limit for the message because 10 bits per second would give a total transmission time of three minutes and any longer might have bored the audience at the transmission ceremony!

The total number of bits, 1679, is divisible by 73 rows of 23 characters, both prime numbers. This suggests that the receiver should lay out the message in those dimensions, revealing an image.

The message was aimed at the M13 globular cluster. It will reach its destination in about 25,000 years. The final picture shows our chemical makeup, our population, our height, our planetary system, and the location of the telescope transmitting the message.

So far, we have not received any messages from outer space. The closest that we think we have come is when, on a hot August night in 1977, Franklin astronomy professor Jerry Ehman recorded a signal on the 21-centimetre wavelength.

“Wow” was what he said, and what he wrote in the margin of his computer print out. The signal was thirty times stronger than the background noise and was on a wavelength that was not for use by terrestrial and satellite sources. Its pattern of movement through the recording devices suggests that it was from the stars and it turned itself on and off.

But what it was and if it meant anything we may never know. The signal has never been detected since.

This article was first published in 1999

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