Zeus, a.k.a. Jupiter, is a ladies man. But going after one of your wife’s own priestesses is probably not advisable. This, alas, did not deter his amorous intents: he cheated on his wife Hera (Juno) with the young mortal female, Io.
Accounts vary as to what happened next: either way, Io was transformed into a heifer. It might have been Hera acting out of rage, or it might have been Zeus trying to protect Io by disguising her. In the latter version, Hera foils Zeus’ plan by asking him for the cow, which she then has guarded by a hundred eyed giant named Argus Panoptes.
Of course, this did not deter Zeus. He sent for the trickster god Hermes, who successfully slew the giant through a mixture of song, story, and violence. Though Io was free, she was still trapped in bovine form, and Hera, ever enraged, sent a gadfly to constantly torment her. This caused Io to flee.
If you’ve ever heard of the international waterway called the Bosphorus, you’ve heard of Io. Bosphoros is a Greek derived word that means the Ox Passage; it is the route Io took as she fled from Hera’s tormenting insect. It’s also the passage way that would lead her to Prometheus.
In the ancient Greek play Prometheus Bound, Io talks to the chained Titan. Prometheus consoles Io, assuring her that her transformation isn’t permanent. He also predicts that one of her descendants would prove to be the greatest of all Greek heroes, Heracles (Hercules) – a useful coincidence for the suffering god, as it is Heracles who eventually liberates the bound Titan.
In the end, Io makes her way to Egypt, is returned to human form by Zeus, marries the Egyptian king, and has children, many of whose descendants go on to have stories of their own (notably Heracles, though others like Hypermnestra, Perseus and Dionysus all play significant roles in Greek mythology).
So what about Io, the physical moon? For starters, if you’re planning your next vacation there, bring lots of water, because there is none. Io might have been better named Tartarus, the Greek “Hell” (which is where Prometheus was bound). It is pock-marked by constant volcanic activity; it is laced with active lava flows, brimming with sulfur. Unless you’re a geologist, this is probably not the place for you (though the named features are nifty, reflecting Io’s mythic journey, a miscellaneous variety of fire deities, and characters and places from Dante’s Inferno).
Maybe this was Hera’s final revenge: Hell hath no fury as a goddess scorned, and the celestial body known as Io appears to embody all of Hera’s indignation (righteous as it may be).
Next stop, Europa, a moon that might be the best, local candidate for extra-terrestrial life…
Featured image taken by NASA’s New Horizon spacecraft showing Io undergoing a volcanic eruption