Io

“ Io could not have put such ideas into words, but they were working, and tearing her heart as a machine rends and wrenches a human limb entangled amongst its whirling wheels. She could hardly reason, but she keenly suffered. Hard did Io strive so to collect her ideas as to find out whether her new discovery would account for that gloom in her husband which had seemed to her so mysterious. Oscar had received no letter from her at Malta, none by the Channel pilot: had her apparent neglect caused him pain, or perhaps a sense of relief? ”

“ Other charged particles can occasionally escape outward and be detected as far away as Earth.
Io is unquestionably a remarkable world. The only planetary body known to be geologically more active than the Earth, it provides many extreme examples to test the theories of geoscientists. Its intimate interconnections with the Jovian magnetosphere and the planet itself provide a unifying theme to the complex processes taking place in the inner parts of the Jovian system. ”

“ Io’s surface, less than ten million years old, is quite young compared to the other Galilean satellites and to other terrestrial bodies, such as Mercury and the Moon. The surface is composed of large amounts of sulfur and sulfur dioxide frost, both of which account for most of the surface color. This picture was taken by Voyager 1. Material deposited by the volcano (see following pictures) can be seen as a white ring near the center of Io. ”

“ Juno was grieved for her servant, and placed his eyes in her peacock’s tail. Io, still persecuted by Juno, wandered over the earth, and at length arrived, faint and weary, on the banks of the Nile. There she prayed Jupiter either to restore her to her original form, or to terminate her misfortunes by death. Juno was touched with compassion, and allowed Jupiter to grant her request. Io was restored to human form, and married to Osiris, king of Egypt; she was afterwards worshipped in that country under the name of Isis. ”

“ Jupiter had seen Io as she was returning from her father’s stream, and had said, “O maid, worthy of Jove, and destined to make I know not whom happy in thy marriage, repair to the shades of this lofty grove (and he pointed at the shade of the grove) while it is warm, and while the Sun is at his height, in the midst of his course. But if thou art afraid to enter the lonely abodes of the wild beasts alone, thou shalt enter the recesses of the groves, safe under the protection of a God, and that a God of no common sort; but with me, who hold the sceptre of heaven in my powerful hand ”

“ Passing in front of the planet are the inner two Galilean satellites. Io, on the left, already shows brightly colored patterns on its surface, while Europa, on the right, is a bland ice-covered world. The scale of all of these objects is huge by terrestrial standards; Io and Europa are each the size of our Moon, and the Red Spot is larger than the Earth. [P-21082C]
While the imaging experiments were in the limelight, the other scientific instruments had also begun to concentrate on the Jovian system. ”

“ Jupiter called Mercury close to his throne and spoke to him.
"I, myself, have lost a cow," he told Mercury. "In fact she is not really a cow at all, but a beautiful maiden named Io, in disguise, and I understand that she lives upon the earth guarded by a watchman named Argus who has a hundred eyes. I should like to rescue the lovely Io and restore her to her proper form, but Argus never closes all of his eyes at once. He sleeps with as many as fifty of them open. ”

“ For a time, a dual nomenclature persisted for the erupting volcanoes on Io. The eruption plumes were given numbers, P1, P2, etc., while the volcanic features were given names taken from the mythology of fire and volcano legends. Thus the “hoof print” of Io was called Pele, for the Hawaiian volcano goddess, and the 280-kilometer-high plume associated with it was called P1. By the time of the Voyager 2 encounter, scientists had prepared maps on which to plot their new discoveries. ”

“ But apparently a part—perhaps 10 tons per second—escapes from Io and is captured by the Jovian magnetosphere. Another part contributes to an ionosphere—a tenuous atmosphere of electrons and ions—that surrounds Io. The injection of several tons of particles each second into the magnetosphere has dramatic consequences that can be seen even from Earth.
Direct evidence of an atmosphere on Io was obtained during the Voyager 1 flyby by the IRIS. In the region near the volcano Loki and its associated “lava lake,” infrared spectra clearly showed the signature of sulfur dioxide gas. ”

“ The presence of this material on Io was confirmed when the infrared IRIS instrument obtained a spectrum of sulfur dioxide gas over the erupting volcano Loki during the Voyager 1 encounter.
Close-ups of Io reveal a wide variety of volcanic phenomena. This Voyager 1 view of an equatorial region near longitude 300° shows several large surface flows that originate in volcanic craters or calderas. At the right edge is a light flow about 250 kilometers long. Another dark, lobate flow with bright edges is just left of center, with an exceedingly dark caldera to its left. ”

“ Careful examination of all the Voyager images of Io, some of which have resolutions as good as 1 kilometer, has failed to reveal a single impact crater. Yet the flux of crater-producing impacts at Io must be even greater than for the other Galilean satellites, because of the focusing effect of Jupiter’s gravity. The absence of craters alone would indicate that Io has an extremely young and dynamic planetary surface, even without the observation of active volcanoes. ”

“ Before Voyager, identification of the surface material on Io presented a major problem to planetary astronomers.
When the sizes and masses of these satellites were measured, astronomers could calculate their densities. The inner two, Io and Europa, both have densities about three times that of water—nearly the same as the density of the Moon, or of rocks in the crust of the Earth. Callisto and Ganymede have densities only half as large, far too low to be consistent with a rocky composition. The most plausible alternative to rock is a composition that includes ice as a major component. ”

“ The gas atoms were not bound gravitationally to Io, but continuously escaped from it to form a gigantic cloud enveloping the orbit of the satellite. Fraser Fanale and Dennis Matson of the Caltech Jet Propulsion Laboratory suggested that bombardment of Io by high-energy particles from the Jovian Van Allen belts was knocking off atoms of sodium by a process called sputtering, releasing these atoms and allowing them to expand outward to form the observed sodium cloud. ”

“ Calisto was above the horizon hanging like a tiny flicker of yellowish-red light above the rounded edge of Jupiter, and Io was invisible behind the planet.
"Five hundred million miles!" said Zaidie, with a little shiver; "that seems an awful long way from home—I mean America—doesn't it? I often wonder what they are thinking about us on the dear old Earth. I don't suppose any one ever expects to see us again. However, it's no good getting homesick in the middle of a journey when you're outward bound. ”

“ Above his head the golden crown of Jupiter was held by a slave who reminded him in the midst of his glory that he was a mortal man. Last came the soldiers shouting Io triumphe and singing songs both of a laudatory and scurrilous kind. ”

“ There was Io, the most bizarre—the one that scientists had thought would be most lunarlike—showing a surface that had apparently been “cooked and steamed and fumed out leaving deposits all over the surface much like you might see around a fumarole at Yellowstone National Park. The fact that these things exhibit such youth makes it likely that the planet is still volcanically active.” There was Europa, with huge linear features unlike those of the other three Galileans—Europa the mystery satellite, waiting for the probing eyes of Voyager 2 to survey it in early July. ”

“ The story of Io probably came from Egypt. Isis was one of the chief divinities of that country, and her worship naturally passed, with their colonies, into foreign countries. Greece received it when Inachus went to settle there, and in lapse of time Isis, under the name of Io, was supposed to have been his daughter, and the fable was invented which is here narrated by Ovid.
The Greek authors, Apollodorus, Strabo, Diodorus Siculus, and Pausanias, say that Io was the daughter of Inachus, the first king of Argos; that Jupiter carried her away to Crete ”

“ Perhaps the most distinctive surface features on Io are the circular or oval albedo markings that surround the great volcanoes. The first of these to be seen was the 300-kilometer-wide white donut of Prometheus, on the equator at longitude 150°. Much more spectacular is the hoofprint of Pele, about 700 by 1000 kilometers. These symmetric rings mark the locations of the kinds of eruptions that generate large fountains or plumes, and may be produced by condensible sulfur or sulfur dioxide raining down from the volcanic fountain. ”

“ They did so on a ram, whose hide became the Golden Fleece (see Phryxus and Helle) . Ino destroyed herself, and was changed by Neptune into a sea-goddess.
Inoa (Ino′a) were festivals in memory of Ino.
[Pg 72] Instrumental Music, see Euterpe.
Io (I′o) was a daughter of Inachus, and a priestess of Juno at Argos. Jupiter courted her, and was detected by Juno, when the god turned Io into a beautiful heifer. Juno demanded the beast of Jupiter, and set the hundred-eyed Argus to watch her. Jupiter persuaded Mercury to destroy Argus, and Io was set at liberty, and restored to human shape. ”

“ The state of the interiors of the Galilean satellites can be judged from their sizes and densities. These cross-sectional views represent the best guess following the Voyager flybys as to the composition and structure of the objects. Io, with a density equal to that of the Moon and a long history of volcanic activity, is a dry, rocky object. Europa is less dense, and it probably has a global ocean of ice as much as 100 kilometers thick over a rocky interior. Ganymede and Callisto both have densities near 2 grams per cubic centimeter, suggesting a composition about half water and half rock. ”

“ It may be remarked that in the foregoing account of Io's wanderings no consistency with our known geography is attainable. ↑ The poet here takes up the journey of Io where he left it in v. 754. The stream which is the limit of the continents is evidently the Kimmerian Bosporos. She now travels towards the sun (i. e., eastward) . This is, in Herodotus, the course of merchants travelling for gold, no doubt, to the Ural Mountains. ”

“ The volcanic plumes on Io appear to be made primarily of sulfur and sulfur dioxide. Both are molten as they emerge from the vent, but they quickly cool as the plume rises 100 or more kilometers into the near vacuum of space. Unlike terrestrial volcanoes, there is almost no gas in the plumes. It requires about half an hour for the fine particles of solidified sulfur and sulfur dioxide snow to fall back to the surface, where they form the colorful rings that mark the major eruptive sites. ”

“ Io is explained as the horned moon, in its various changes and wanderings. Argus is the heaven with its myriad stars, some of them shut, some blinking, some always agleam. The wand of Hermes and his music may be the morning breeze, at the coming of which the eyes of heaven close (Cox, 2, 138; Preller 2, 40) . The explanation would, however, be just as probable if Mercury (Hermes) were a cloud-driving wind. Pan and the Syrinx: naturally the wind playing through the reeds, if (with Müller and Cox) we take Pan to be the all-purifying, but yet gentle, wind. ”

“ We see tonight the beginning of the exploration of four new worlds. We’re racing through time and space at an incredible rate—the rate at which we are learning things is awe-inspiring in itself.” Callisto was still too far away to see well “but the things we’re seeing on the closer three satellites have really got us charged in anticipation.” Ganymede—“What can I say? Loops and swirls and incredible patches that are difficult now to hazard a guess about.” Io—an eerie-looking red, orange, and yellow world—“this one we’ve got all figured out. ”

“ She is entrusted by Juno to the care of Argus; Mercury having first related to him the transformation of the Nymph Syrinx into reeds, slays him, on which his eyes are placed by Juno in the tail of the peacock. Io, having recovered human shape, becomes the mother of Epaphus. ”

“ Aurora, the Dawn-goddess, up bright and early to open the sun gates for Apollo, saw the handsome hunter on the sky slope decked with red and white and yellow lights of stars. Like Diana, she loved him immediately, but, in the words of the poets, he pales before her colorful radiance as she reaches upward to announce the coming of the sun. Because dawn takes away the stars, Orion is said to have been carried away by this goddess and even yet this story may be seen enacted when watching the glory of Orion captured by Aurora as she flashes rosy-tinted in the east. ”

“ Now when that is done, that Jupiter and Venus have given themselves to the Power of the Sun, then Jupiter forces no more upwards, but Mars and Mercury do continually more and more wind up the Stalk from the Earth on high; Jupiter stays still above in the inward and outward Sun's Power, and there is the pleasant Conjunction with Time and Eternity, there the Eternity beholds itself in an Image in the Time. ”

“ But when we got beyond the atmosphere, and the earth still continued to recede below us, its aspect changed. The cup-shaped appearance was gone, and it began to round out beneath our eyes in the form of a vast globe—an enormous ball mysteriously suspended under us, glimmering over most of its surface, with the faint illumination of the moon, and showing toward its eastern edge the oncoming light of the rising sun. ”