![]() In the two images below, eruptions about a year apart produced lava flows that contributed to the ridged and fractured surface topography. Several plumes were imaged during different orbits by the Galileo explorer.Īctive eruption of lava was also discovered. One of the more exciting discoveries from the Galileo images was active eruption plumes, extending more than 300km above the moon surface (the blue colour is probably due to dispersion of light by plume aerosols). Frequent volcanic eruptions of lava and fine (sulphur?) particles mean that Io’s surface is constantly being renewed a consequence of this is that impact craters are poorly preserved because they too are recycled. Spectacular images taken by the space craft Galileo in 1995 show a moon splashed with colour, a kind of post-impressionist experiment NASA refers to it in more colloquial terms as a giant pizza. Sulphur is also the main constituent of Io’s thin atmosphere, but in this case as sulphur dioxide. The outer solid carapace is an intriguing mix of sulphur in solid form at the surface and silicate rock. The core of Io probably consists of iron or iron sulphide, surrounded by a mix of solid and molten rock, the composition of which may be similar to that on earth. In comparison, Jupiter’s average density is little more than that of water, at 1.3g/cm 3. Io is quite different to the other Jovian moons in that it’s density is more like that of the rocky planets (Earth, Mars, Venus, Mercury) – in fact it is almost the same density as Mars (3.5g/cm 3). These tidal forces generate enough heat to melt rock and sulphur. ![]() The resulting gravitational forces produce huge tides such that the surface bulges up to 100m. Io’s elliptical orbit brings it to about 420,000 km from the gas giant. It is also one of the most unusual planetary bodies in our solar system, and the only one with active volcanism – over 400 eruptive centres have been mapped. Io is the third largest of Jupiter’s 60 (known) moons, fractionally larger than our own moon, and one of the four moons discovered by Galileo in 1610. Io’s memory now survives as a planetary body one of the Galilean moons of Jupiter is named after her (to be named a moon of the Roman God Jupiter, seems like a historical slap in the face to the Greek deity). One such misdirection was Io, a mortal woman, who had the misfortune to be turned into a heifer by Zeus, to hide the infidelity from Hera. One of his minor portfolios was the upholding of Honour, but as mythology relates, he didn’t put much energy into that particular task he was a philanderer, much to the annoyance of his own wife, Hera (I guess his energies were directed elsewhere). Zeus, the head-honcho of assorted Greek gods, heroes, nymphs, and mortals, was chiefly the God of the Sky, or Heavens. ![]()
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