During it's long journey through the universe, should any intelligent beings come across Pioneer 10 (or Pioneer 11, which carries a copy of the same plaque), they'll be greeted with a pictorial engraving from humanity in the form of a 6 by 9-inch gold anodized plaque bolted to the spacecraft's frame. The plaque design attempts to convey as much data about humans and the Earth as possible using simple line diagrams, in the hope that whatever beings may find it can learn whence and from where the probe originated.
Among other things, it depicts a naked man and woman, with the right hand of the man raised as a sign of good will. It also indicates the layout of our solar system, as well as our sun's position relative to a number of pulsars, so that our location can be triangulated from fixed points in space.
When the plaque's design was revealed to the general public, a number of people were upset about it for various reasons. Because it depicts nudity, there was a huge uproar about NASA "wasting" taxpayer money to send "obscenities" into space. Clearly, the people voicing such pseudo-moral objections were "morons." Or rather, they had the unfortunate character flaw of being unable to separate an obscene image from a benign, scientifically useful drawing.
There were also many who criticized the complexity of the message, indicating that it would not be immediately understandable to a completely alien civilization. This is certainly true, but the plaque's designers did not intend for the message to be instantly detectable, only for it to be precise and informative. If found, its discoverers can spend as much time as necessary to decode its message, even if it takes generations.
Still other critics warned that showing a map to the probe's planet of origin may invite a hostile race to find and attack the Earth. This risk does exist, but even in the extremely unlikely event that the first star a Pioneer probe encounters (two million years from now) is home to a hostile race bent on our destruction, they must first A) detect the fast-moving piece of space debris, B) capture it, C) decode the plaque's message, D) locate our planet, and E) traverse the distance. This means that at the soonest, such aggressors would be arriving in about three million years.
In point of fact, the chances of the probe ever being discovered by any civilization-- hostile or otherwise-- are virtually non-existent, even if the universe is teeming with life. Something so tiny is just lost against the enormity of space. So why even bother including message? It seems that it was motivated by pure, unadulterated optimism. On the off chance that the someone, somewhere ever stumbles across our humble probe, it can't hurt to tell them a little about ourselves.
The graphic representation of the message (pictured) has color added to indicate the different sections. It was originally transmitted in binary, using prime digits to give clues on how to arrange the pixels.
Among other things, it attempts to depict a human, the structure of DNA, and our solar system, but clearly it can't represent any of those things very clearly in the given space. However, if the message is ever received and decoded, it will certainly be clear to the recipients that it originated from an intelligent source. If nothing else, aliens should be able to deduce the existence of the Atari 2600 game console. If they have a reply, we can expect to receive it in about 50,200 years, assuming we're still able to listen for it.
But the most ambitious information payloads that we've blasted into the cosmos are those attached to the sides of the Voyager 1 and 2 probes, launched in 1977. Each probe has a copy of the same gold gramophone record, which is encoded with sounds and images intended to portray the diversity of life and culture on Earth. The probes also provide a cartridge and a needle for use in reading the records' contents.
Pictured is the gold-plated protective cover, which is engraved with diagrams describing how to extract the data from the disk, and the same pulsar diagram from the Pioneer probes indicating the record's place of origin. NASA also had the cover electroplated with Uranium 238, so an advanced race might determine the record's age by measuring the amount of radioactive decay.
President Carter included a spoken greeting on the record, which included the following:
"We cast this message into the cosmos . . . Of the 200 billion stars in the Milky Way galaxy, some - - perhaps many - - may have inhabited planets and space faring civilizations. If one such civilization intercepts Voyager and can understand these recorded contents, here is our message: We are trying to survive our time so we may live into yours. We hope some day, having solved the problems we face, to join a community of Galactic Civilizations. This record represents our hope and our determination and our goodwill in a vast and awesome universe."
Of course it is unlikely that any intelligent race will ever stumble across one of our derelict spacecraft, and even if they do, the time scales and distances involved are staggering. Moreover, it's doubtful that a completely alien intelligence can discern the whole meaning of the diagrams for lack of a common frame of reference. But there would be little doubt that the object is the product of an intelligent race of people, which is perhaps the most important message to convey.
So it seems that the act of including these messages from humanity is really a symbolic statement rather than a serious attempt to communicate with other civilizations. But long after humanity has died off, and the Earth is burned to a crisp by her dying sun, these tiny messengers will continue to tote little pieces of our history throughout the universe. And maybe after drifting for millions of years, one of our messages-in-a-bottle will be discovered, and possibly mark the most exciting event in another civilization's history.