There are, in fact , thirteen of them. We can identify them, of course, because we launched them. But to potential extraterrestrials out there, Pioneers 1 through 11 and Voyagers 1 and 2 would indeed be UFOs. They may no longer talk to us, but like the two Voyagers, two Pioneers continue to hurtle through space on their way, respectively, to the constellations of Alderberan and The Eagle. It will take them two million years to get to Alderberan and four million to reach the Eagle.
As you can see, I am still overwhelmed by the apparent infinity of the Universe. (I am avoiding the prefix “quasi-” which the dictionary defines simply as “seemingly”(adv.) or “seeming” (adj.), whence its use in the telescoped word “quasar”, which even non-engineers and other ignoramuses know means a “QUASI-stellar radio source”). “Relativity” had a precise meaning for Einstein which only intelligent people like engineers can understand. The rest of us may be excused for using the word in a broader sense, when we compare and contrast figures like those just mentioned with figures we non-engineers learned from “The Farmer’s Almanach” and comic-books. Life, we are told, has existed on earth for four billion years. We humans have been around only 200,000 years. Whence Sagan’s brilliant piece of pedagogy, squeezing 13.7 billion years since the Big Bang into one cosmic year, which puts the beginning of human life just a few moments before midnight on December 31 ! This sort of relativity leaves little reasonable room for the God-hypothesis.
Science-fiction writers could have a ball, telling the story, 4,000,000 years from now when inhabitants of the planet Woodyableevit observe, capture and examine the UFOs somebody (us) sent them a l – o – n – g time ago. They may or may not appreciate Beethoven or cotton on immediately to the scientific data we shared with them. But if they didn’t know it before, they will surely be impressed, as we are, with the vastness, the immensity, of timespace to which our Pioneers and Voyagers bear witness. I hope none of them imagines, in a kind of Cosmic Cargo Cult, that our little UFOs are a gift of God from the other side of (the) Heaven(s). At least the engineers among them could be expected to know better.