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Jupiter\u2019s moon Io is a volcanic powerhouse. It\u2019s the most geologically active world in the Solar System, sporting more than 400 spouting volcanoes and vents on its surface. Has it always been this way? A team of planetary scientists says yes, and they have the chemical receipts to prove it.<\/p>\n
<\/p>\n In a recent paper, the team headed by CalTech scientist Katherine de Kleer cites data from millimeter observations of elemental isotopes found in Io\u2019s eruptions. They found that chemicals like chlorine and sulfur exist in higher quantities at Io than in comparable places in the Solar System. Analysis shows that Io hasn\u2019t just started erupting lately\u2014it\u2019s been going on for most of its history. And, it\u2019s so volcanic that it practically resurfaces itself every million years or so.<\/p>\n The discovery of volcanism on Io was one of the major results of the Voyager mission. As the two spacecraft swept past Jupiter in 1979, their images revealed Io\u2019s volcanic features and plumes. Since that time, the Galileo, Cassini-Huygens, New Horizons, and Juno missions also sent images. The Jovian system and its moons are also frequent targets for ground- and space-based observatories, including Hubble Space Telescope and JWST. <\/p>\n Io is the fourth-largest Jovian moon and is one of the four Galilean satellites. It orbits closest to Jupiter and gets pulled by a gravitational tug-of-war between Jupiter and the other Galilean moons. The result is a process called \u201ctidal heating\u201d deep inside Io, produced by friction. That generates heat, which melts Io\u2019s interior, and opens up vents so that the heat and melted material can escape to the surface.<\/p>\n This little moon is mostly silicate rock atop an iron or iron sulfide core. The surface is scarred with volcanoes and deformed by compressional forces beneath the crust. The most obvious features are the volcanic mountains, plumes, and lava flows. Currently, Io\u2019s volcanoes resurface the landscape at a rate of about 0.1 to 1.0 cm per year. They also paint its surface in an amazing array of colors. During the Voyager 2 flyby, people often compared its appearance to a pizza. The colors come mainly from sulfur and sulfurous compounds deposited across the landscape.<\/p>\n Normally, geologists would look at its surface and count craters to get an idea of its age. But, since volcanic flows erase craters, there\u2019s no easy visual way to determine how long volcanic features have been around. However, it turns out that abundances of certain isotopes of sulfur and other elements could provide a good record the history of volcanism on Io.<\/p>\n Io has probably lost mass to space throughout its history. de Kleer and her colleagues point out that its supply of volatile elements should be highly enriched in heavy stable isotopes. That\u2019s because atmospheric escape processes generally favor the loss of lighter isotopes. They suggest that stable isotope measurements of volatile elements, such as sulfur and chlorine, could give accurate details about the history of volcanism at Io. So, it makes sense, then, to do a thorough chemical analysis of Io\u2019s volcanic emissions now and extrapolate back.<\/p>\n Understanding Io\u2019s current chemistry, requires, among other things, a good idea of its mass-loss history. Io\u2019s mass loss occurs because of collisions between atmospheric molecules and energetic particles trapped in Jupiter\u2019s magnetosphere. If this continued over Io\u2019s history, then its chemistry should provide evidence of the volcanic past. In their paper, the team discusses the assumptions they made, including estimates of Io\u2019s initial inventory of sulfur, as well as possible early mass-loss rates that could affect its current abundances of sulfur and chlorine\u2014two elements that help determine past and present volcanism.<\/p>\n To get that history, team used the Atacama Large Millimeter Array to observe gases in Io\u2019s atmosphere. The goal was to measure SO2, SO, NaCl, and KCl in various forms and determine the ratios of 34<\/sup>S to 32<\/sup>S and 37<\/sup>Cl to 35<\/sup>Cl. After analyzing the data, the team found that Io has lost at least 94 to 99 percent of its available sulfur over time. In addition, the measurements show enriched levels of chlorine. This probably indicates that Io has been volcanically active throughout time. It\u2019s also possible that this tiny moon has experienced higher rates of outgassing and mass loss early in its history. More measurements should help scientists constrain Io\u2019s volcanic activity even more tightly.<\/p>\n Isotopic Evidence of Long-lived Volcanism on IoFacts about Io<\/h3>\n
Analyzing Io\u2019s Chemistry<\/h3>\n
For More Information<\/h4>\n
Violent Volcanoes Have Wracked Jupiter\u2019s Moon Io for Billions of Years<\/p>\nLike this:<\/h3>\n