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• THE LUNAR EXPLORER ARCHIVES
• MOON
• MARS
• SOLAR SYSTEM
• DEEP SKY

A R C H I V E S

Io is the innermost of the 4 (four) Galilean moons of the Giant Gas-Planet Jupiter and, with a diameter of approx. 3640 Km (such as about 2260 miles), Io is the fourth-largest moon in the Solar System. With over 400 active Volcanoes, Io is the most geologically active object in the Solar System. This extreme geologic activity is the result of the phenomenon known as "Tidal Heating", such as a sort of friction that is generated, within Io's interior, as this moon is - litterally - pulled away and apart by and between Jupiter and the other 3 (three) Galilean moons — such as Europa, Ganymede and Callistus.

There are several Volcanoes on Io which are capable to produce huge Plumes of Sulphur and Sulphur Dioxide that can climb as high as about 500 Km (approx. 300 miles) above its Surface (one of these Plumes, coming from the Volcano named Prometheus, is visible in the frame, on the upper right, at about one o'clock - see the EDM for a slightly saturated magnification of that Surface Relief). Io's Surface is also dotted with more than 100 Mountains that have likely been uplifted by phenomena of extensive compression which occurred at the base of the moon's Silicate Crust, and some of these Mountains are taller than Earth's Mount Everest. Unlike most of the natural satellites (or moons) existing in the Outer Solar System (and which are mostly composed of Water-Ice), Io is primarily composed of Silicate Rock surrounding a molten Iron (or Iron Sulfide) Core.

Most of the Surface of Io is characterized by extensive Plains, coated with Sulphur and Sulphur Dioxide Frost. Io's Volcanism is responsible for many of the satellite's unique features. Its Volcanic Plumes and Lava Flows produce large Surface changes and, in a way, "paint" the Surface in various shades of yellow, red, white, black, and green (a phenomenon that is largely due to allotropes and compounds of Sulphur). Numerous (and VERY extensive) Lava Flows, whose length can reach up to 500 (and even more) Km, also mark the Surface. It is important to underline that such an hyper-Volcanism is the source of all the Gaseous Elements which are necessary to sustain Io's thin and patchy Atmosphere, as well as Jupiter's extensive Magnetosphere. Furthermore, Io's Volcanic Ejecta also produce a large Plasma Torus around Jupiter (note that the so-called "Heavy Ions" existing in the Plasma Torus, migrate outward, in such a way and manner that their pressure inflates the Jovian Magnetosphere to more than twice its expected size; in addition to that, some of the more energetic Sulphur and Oxygen Ions fall along the Magnetic Field of Io into its Atmosphere, thus creating beautiful Aurorae).

If observed from Earth, Io remained nothing more than a point of light, until the late 19th and early 20th Centuries, when it became possible to partially resolve its large-scale Surface Features, such as the dark red Polar and bright Equatorial Regions. In the AD 1979, the two NASA - Voyager 1 and 2 Spacecrafts revealed Io to be a geologically active world, with numerous Volcanic Features and, as we already mentioned hereabove, several large and tall Mountains, as well as an always Young Surface with no obvious (---> clearly visible) Impact Craters (whose traces have been rapidly cancelled by the continuous renewal of the Surface). The NASA - Galileo Spacecraft performed several close Fly-Bys in the late 1990s and early 2000s, so obtaining a lot of data about Io's Internal Structure and Surface Composition. All these  aforementioned Spacecrafts also allowed Scientists to better understand the relationship between Io and Jupiter's Magnetosphere as well as they uncovered the existence of a "Radiations' Belt" centered on Io's orbit.

This frame has been colorized in Absolute Natural Colors (such as the colors that a human eye would actually perceive if someone were onboard the NASA - Voyager 1 Spacecraft and then looked outside, towards the Jovian moon Io), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team.