Io is a Galilean moon of Jupiter, discovered by Galileo Galilei. It is the most geologically active body in the solar system, with over 400 volcanoes and mountains taller than Mt. Everest. It lacks true craters but has small volcanic depressions called paterae. The New Horizons spacecraft observed an eruption in the Tvashtar Paterae volcanic region in 2007. Io’s intense geological activity means it would be a challenge for human colonists to make it habitable.
Io is a moon of Jupiter. Together with Callisto, Europa and Ganymede, Io is a Galilean moon, discovered by the Italian astronomer Galileo Galilei using one of the first telescopes. It is the innermost of the Galilean moons, closely exposing it to Jupiter’s powerful magnetosphere and ambient radiation. Due to tidal heating from its orbit around Jupiter, Io is one of the most geologically active bodies in the solar system, with over 400 volcanoes.
When Voyager first saw evidence of volcanism on Io, it was the first discovery of volcanism on an extraterrestrial world and caused great excitement in the scientific community. Io’s unusual craterless surface has meant that it was among the most fascinating of the Jovian moons to planetary scientists. Covered in frosts of sulfur and sulfur dioxide, but with a thin silicate core, the volcano-riddled surface of Io makes it resemble a yellow pizza. On Io’s trailing hemisphere, a huge volcano, Pele, erupts steadily, surrounded by a giant red ring of volcanic fallout. It was the Pele eruption that first alerted scientists that Io was volcanically active.
Io’s intense geological activity has given it mountains taller than Mt. Everest. Boösaule Montes has peaks over 10 miles high. In total, Io has around 150 mountains.
Though it lacks true craters, Io is covered in small volcanic depressions called paterae, named after a type of shallow Roman bowl. These depressions are usually bounded by steep cliffs and appear similar to terrestrial calderas, although the mechanism of formation appears to be different and is still elusive. The largest patera is 125 miles in diameter. In 1999 and 2000, the Galileo spacecraft observed active lava flows near paterae.
When the New Horizons spacecraft passed Io on March 1, 2007 on its way to Pluto, it observed the eruption in the Tvashtar Paterae volcanic region, a 330 km high plume spewing sulfuric magma over a similar region. If Io had much atmosphere, it would smell terrible. Continued eruptions of sulfur mean that Io will be a real challenge for the human colonists. To make Io habitable, it would likely need to adjust its orbit away from Jupiter, calming its Hadean geology.
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