Io is the innermost of the four Galilean Moons of Jupiter (the four large moons discovered by Galileo Galilei in January 1610), and is one of the most distinctive bodies in the Solar System, with a surface dominated by a series of extensive volcanic fields. The volcanism is thought to be caused by tidal forces, as Io is pulled by the gravitational forces of both Jupiter and the other large Galilean Moons, deforming and heating the moon's interior. This has led to a body unlike any other in the Outer Solar System, with no significant ice or hydrocarbon deposits (presumably lost due to the heat of the volcanic activity) and a silicate rock surface surrounding an iron or iron-sulphur core.
The Galilean Moon Io, as imaged by the Galileo Spacecraft in 1995. NASA/JPL/University of Arizona/Wikimedia Commons.
In a press statement released on 13 July 2018, scientists from NASA described the discovery of a new volcanic field on Io, close to the moon's South Pole and about 300 km from the nearest previously discovered field. This was revealed in an image of Io taken by the Jovian InfraRed Auroral Mapper instrument on the Juno Spacecraft during a flyby on 16 December 2018.
This annotated image highlights the location of the new heat source close to the south pole of Io. The image was generated from data collected on 16 December 2017, by the Jovian Infrared Auroral Mapper (JIRAM) instrument aboard NASA's Juno mission when the spacecraft was about 470 000 kilometres from the Jovian moon. The scale to the right of image depicts of the range of temperatures displayed in the infrared image. Higher recorded temperatures are characterised in brighter colours – lower temperatures in darker colours. NASA/JPL/Caltech/Southwest Research Institute/Agenzia Spaziale Italiana/Insituto Nazionale di Astrofisica/Jovian Infrared Auroral Mapper .
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