What Lies Beneath Jupiter's Pretty Clouds

For something that was to have been done and thrown away three years ago, NASA's Juno spacecraft has a busy schedule ahead exploring Jupiter and its big moons. From a report: The spacecraft entered orbit around Jupiter on July 4, 2016, and has survived bombardment from intense radiation at the largest of the solar system's planets. It is now finishing its primary mission, but NASA has granted it a four-year extension and 42 more orbits. Last week, it zipped past Ganymede, Jupiter's largest moon. "Basically, we designed and built an armored tank," said Scott J. Bolton of the Southwest Research Institute in San Antonio, who is the mission's principal investigator. "And it's worked." Jupiter is essentially a big ball of mostly hydrogen, but it has turned out to be a pretty complicated ball. The mission's discoveries include lightning higher up than thought possible, rings of stable storms at the north and south poles, and winds extending so deep into the interior that they might push around the planet's magnetic fields. "I think this has been a revelation," said David J. Stevenson, a professor of planetary science at the California Institute of Technology and a co-investigator on the mission. Juno's highly elliptical path, pitched up at almost a 90-degree angle to the orbits of Jupiter's moons, passes over the planet's north and south poles. On each orbit, Juno swoops in, reaching a top speed of 130,000 miles per hour as it passes within a few thousand miles of Jupiter's clouds.

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