We have always asked the question, “Are we alone in the Universe?” Until now we firmly do not have an answer. But there is a little dreamer kid in all of us, including scientists. Which is why when NASA announced it would be sending a probe to deep space, they decided to include a message to any extraterrestrials that may come across the probe in the distant future. Pioneer 10 and Pioneer 11, launched in 1972 and 73 respectively, the two probes tasked to set out on this amazing journey, had prime purposes of flying by Jupiter and Saturn (Pioneer 10 only visited Jupiter, while 11 visited both) to take measurements and pictures which would be sent back to Earth. The scientists knew that the Pioneer probes had a one-way ticket from Earth, so they decided as an added bonus that once the encounter with the planets was done, they would maneuver the probes so that they would use their final stop planet as a gravitational slingshot, accelerating the probes to achieve escape velocity from our Solar System. Essentially, we flung them out towards the stars in an attempt to expand Man’s sphere of influence to beyond our lonely Sun’s gravitational system.
But then the question arose, what if, by some small chance, an intelligent alien came across our probe? What would they think? More importantly, what would we want to try to tell them? NASA tasked famed astronomer and cosmologist Carl Sagan with coming up with a plaque to put on the probe. Sagan came up with this image. The highlights of the plaque are both a male and female naked human being, standing side beside and in front of a to scale drawing of the probe itself, so as to give any alien a sense of size. Additionally the man’s hand is raised as a greeting sign, though Sagan admitted that this welcoming sign would most likely not be understood by an alien, though it does provide a sense of how our bodies operate. The most important part of the plaque lies at the top left corner; it is a picture of two hydrogen atoms, one with electron spin up, the other spin down. When an electron goes from spin up to down, there is a very small energy change which releases a photon of wavelength 21 centimeters. This 21 centimeters is a universal measurement, an presuming an intelligent alien, they would know this (perhaps not by the unit centimeters but by their own unit). From this measurement, assigned the binary number 1 as evidenced by the dash between the two atoms and the straight line inscribed there, sets up a binary system which can be used to describe other numbers. This system may not be understood by an alien but it is the best chance we have at a language they would understand. Using the system, we spell out the location of planet Earth in relation to nearby pulsar stars, as evidenced by the lines radiating from a center point at the left of the plaque. Those lines are actually binary codes which describe the period of the stars pulsation and its distance from Earth. An intelligent alien would be able to pick out these stars in its sky and possible use them to find Earth (for our good or for bad is another question! We don’t know if we want them coming to us!). Finally, along the bottom is a rough picture our solar system, with all the planets in order, along with their distances from the Sun in binary code. Then there is an area describing the path of the probe out of our solar system. The alien may not know what the arrow represents, but it was worth a shot. We may never know if anyone comes across this probe, but if they do, let us hope they can decipher it!
For more of our attempts to communicate with aliens, see the Voyager vinyl records!
