Io

In Greek mythology, Io was a young woman who was loved by Zeus, king of the gods. His attentions toward her aroused the jealousy of his wife, Hera *, and both deities used their powers in various ways to try to gain control over Io.

The daughter of the river god Inachus, Io was a priestess at one of Hera's temples. Zeus fell in love with her and seduced her. When Hera learned about Zeus's behavior, she turned the girl into a white cow. In some versions of the myth, it was Zeus who transformed Io into the cow, to conceal her from Hera.

After tying Io the cow to an olive tree, Hera sent Argus, a giant with 100 eyes, to watch over her. Zeus responded by sending the messenger god Hermes to rescue Io. Hermes put Argus to sleep by singing and telling stories, and then he killed the giant.

Angry that Io was released, Hera sent a gadfly—a type of insect that bites animals—to torment her. Io wandered distractedly until she reached Egypt. There, after Zeus turned her back into a woman, Io gave birth to a son named Epaphus. Many of Io's descendants returned to Greece. Among them were Cadmus, Perseus, and Hercules.

deity god or goddess

See also Argus; Cadmus; Hera; Hercules; Hermes; Perseus; Zeus.

Io (Jupiter I) One of the Galilean satellites and the most geologically (and especially volcanically) active body in the solar system, its volcanoes being due to heat generated by tidal heating and eruption temperatures reaching more than 1000 K. Io radiates more heat than it receives from the Sun. The Voyager spacecraft observed 9 volcanic eruptions. It has a metallic core, rock mantle, and a rocky surface covered with sulphur and sulphur compounds, including sulphur dioxide frost. Io was discovered in 1610 by Simon Marius and Galileo. Its equatorial radius is 1821.3 km; mass 8.93 × 10²² kg; mean density 3530 kg/m³; visual albedo 0.61; mean distance from Jupiter 421 600 km; orbital period 1.769138 days; rotational period 1.769138 days; surface temperature about −143°C, but with one volcanic feature with a temperature measured as 17°C.

Io in Greek mythology, a priestess of Hera who was loved by Zeus. Trying to protect her from the jealousy of Hera, Zeus turned Io into a heifer. Hera sent a gadfly to torture the heifer, which then fled across the world and finally reached Egypt, where Zeus turned her back into human form.

The Bosporus (‘cow's passage’) and the Ionian Sea are reputed to have been crossed by Io, and derive their names from her story.

Io Large, innermost satellite of Jupiter. It was discovered by Galileo in 1609–10, and is larger than the Moon. It is more than 3600km (2200mi) in diameter, and is 422,000km (262,000mi) above the surface of the planet.

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