At Saturn, the Esa/Nasa Cassini-Huygens mission revealed something similar for the moons Enceladus and Titan. Galileo data also showed that Jupiter’s moon Ganymede and maybe even Callisto have interior oceans. Jupiter possesses three other large moons: Io, Ganymede and Callisto. But compared with Europa, it’s actually a thin veneer,” says Cockell.Īnd it is not just Europa. “On Earth, the ocean looks very substantial. The Conamara Chaos on the surface of Europa. Because Europa is only a quarter of Earth’s diameter, the water must be spread around the moon in a global ocean, 25 to 95 miles deep, beneath a 10- to 15-mile-thick ice crust. But the biggest surprise was the amount of water that the theoreticians needed to account for the signals: more than twice the amount of water found in all of Earth’s oceans. One region in particular, called the Conamara Chaos, in honour of a rugged coastline in Ireland, became the poster child portrait of the moon. The currents in this water were generating their own small magnetic fields that were then interfering with Jupiter’s, producing the unexpected readings.Īdditionally, images from those close flybys showed ice floes on Europa’s surface. The signals suggested the presence of salty water beneath Europa’s icy surface. Eventually, after 12 close flybys, there was enough data for her team to present an answer. To collect more of these strange readings, Margaret Kivelson, the instrument’s principal investigator, and others helped persuade Nasa planners to keep extending the mission. There may be six to eight times more water on Ganymede than on Earth Olivier Witasse What changed was a set of measurements from a Nasa mission in the 1990s that, at first, made no sense.Įvery time the Galileo spacecraft drew near to Europa, one of Jupiter’s icy moons, readings from the magnetometer instrument indicated that something inside the moon was interfering with the mighty magnetic field generated by Jupiter. Photograph: Lionel Bonaventure/AFP/Getty Images Juice at an Esa facility, Toulouse, south-western France, April last year.
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