Io (moon)

Io ({{IPA2|?a?o?}}, eye'-oe, Greek Ιώ) is the innermost of the four Galilean moons of Jupiter. It is named after the Greek mythological figure Io, one of the many lovers of Zeus (who is also known as Jupiter in the Roman mythology).

Physical characteristics

Unlike most moons in the outer solar system, Io may be somewhat similar in bulk composition to the terrestrial planets, primarily composed of molten silicate rock. Recent data from the Galileo orbiter indicates that Io has a core of iron (perhaps mixed with iron sulfide), the core's radius being at least 900 km.

Related Topics:
Silicate - Rock - Iron - Iron sulfide

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

When Voyager 1 first returned images of Io in 1979, scientists expected to see numerous craters, the density of which across Io's surface would give clues to the moon's age. However, they were surprised to discover that Io's surface is almost completely lacking in craters, due to the tremendous amount of volcanic activity constantly reshaping the landscape. Since the surface features visible today were formed relatively recently, the Ionian surface is described as "young", as is the terrestrial surface. In contrast, celestial bodies with heavily cratered features, such as Earth's Moon, are considered to have "old" surfaces, since they have remained in their current state for billions of years.

Related Topics:
Crater - Moon

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

In addition to volcanoes, Io's surface includes nonvolcanic mountains, numerous lakes of molten sulfur, calderas up to several kilometres deep, and extensive flows hundreds of kilometres long of low-viscosity fluid (possibly some form of molten sulfur or silicate). Sulfur and its compounds take on a wide range of colors and are responsible for Io's variegated appearance.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Analysis of the Voyager images led scientists to believe that the lava flows on Io's surface were composed mostly of various compounds of molten sulfur. However, subsequent ground-based infrared studies indicate that they are too hot for liquid sulfur; some of the hottest spots on Io may reach temperatures as high as 2000 K, 1300 K higher than the boiling point of sulfur, though the average is much lower, at around 130 K. One current theory is that Io's lavas are molten silicate rock. Recent Hubble Space Telescope observations indicate that the material may be rich in sodium. There may be a variety of different materials in different locations.

Related Topics:
Lava - Infrared - K - Hubble Space Telescope - Sodium

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Io has a thin atmosphere composed of sulfur dioxide and perhaps other gases.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Unlike the other Galilean satellites, Io has little or no water. This is probably because Jupiter was hot enough early in the evolution of the solar system to drive off the volatile elements in the vicinity of Io, but not hot enough to do so farther out.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~