Water geysers on Enceladus bloom largest when the moon is at its furthest point from Saturn and the fractures sourcing the geysers are being pulled open.īut the new study did not find evidence that Loki Patera keeps the same time as Io's two-day orbit around Jupiter. Such a fluctuation with daily orbit occurs on Saturn's moon Enceladus, which has an underground ocean that spurts out through cracks in the moon's frozen surface. Researchers studying the more than 400 volcanoes on Io have looked for evidence that they erupt on the same beat. This generates enough heat from friction within the materials of the moon's interior to melt rock into magma. The shifting pull of Jupiter and the other moons stretches and compresses Io on its two-day orbit around Jupiter. Io's distance from Jupiter changes over the course of its elliptical orbit, so it experiences a different amount of Jupiter's gravity as it circles the massive planet. This 1:2:4 rhythm means the pull of gravity from the other two moons repeats consistently as Io orbits around Jupiter. Credit: Matma Rex/WikicommonsĮuropa's orbit around Jupiter is twice as long as Io's, and Ganymede's orbit is twice as long as Europa's. Orbital resonances of the Galilean moons of Jupiter. The moon is stuck in an eccentric orbit because it resonates with Jupiter's largest moons, neighboring Europa and Ganymede, caught between their influence and the massive gravity of Jupiter. Io has a hot interior because its tight orbit around Jupiter is not circular. "We know almost nothing about what Io's magma chambers and conduits are like, so Loki Patera's behavior is giving us a small window into an area where we currently have zero information," said de Kleer. Understanding this dynamic may provide clues to Io's mysterious interior as well as the interiors of other bodies in the solar system warmed by a fluctuating pull of gravity, an effect called tidal heating. "As far as anyone has been able to tell, there is no variation in Io's volcanoes on this 1.77-day scale, so it's a bit counterintuitive that we would see a response over the longer period, when the changes in stress are lower." "The stresses on Io's interior vary a lot during that 1.77-day orbit," said Katherine de Kleer, a planetary scientist at the California Institute of Technology and the lead author of the new study. The new study, which analyzed 271 nights of observations of Loki Patera from Hawaii's Keck and Gemini North telescopes from 2013–2018, and more sporadic observations dating back to 1987, suggests the gentler, 500-day cycle may act on the right timescale to move magma and bring it to the surface of the moon in an eruption. Internal friction from these stresses generates the heat that powers Io's volcanoes, but fluctuating stresses during the short period of Io's orbit don't appear to squeeze magma to the surface. The new results are surprising because volcanoes on Io do not erupt in time with larger fluctuations in the far greater stresses inflicted on Io during the moon's 1.77-Earth-day orbit around Jupiter. A new study in the AGU journal Geophysical Research Letters finds Io's most powerful, persistent volcano, Loki Patera, brightens on a similar timescale to slight perturbations in Io's orbit caused by Jupiter's other moons, which repeat on an approximately 500-Earth-day cycle.
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