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Satellite evades ‘day of reckoning' to discover puzzling weather phenomenon on Jupiter

Brian Lada

At first glance, these newly released images by NASA may look like lava churning in the heart of a volcano, but they reveal otherworldly storm systems whirling in a way that surprised scientists.

The swirls in the photos are cyclones around Jupiter's south pole, captured by NASA's Juno spacecraft on Nov. 3, 2019. Juno has been orbiting the solar system's largest planet since 2016 and has seen these polar cyclones before, but its latest flight over this region of the planet revealed a startling discovery - a new cyclone had formed unexpectedly.

Six cyclones can be seen at Jupiter's south pole in this infrared image taken on Feb. 2, 2017, during the 3rd science pass of NASA's Juno spacecraft. (NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM)

Prior to its early November pass, Juno had photographed five windstorms arranged in a uniform, pentagonal pattern around one storm sitting stationary over the south pole.

"It almost appeared like the polar cyclones were part of a private club that seemed to resist new members," said Scott Bolton, Juno principal investigator from the Southwest Research Institute in San Antonio.

It is unclear when exactly the new cyclone formed, but it changed the arrangement of the storms from a pentagon to a hexagon.

Winds in these cyclones average around 225 mph, according to NASA, wind speeds higher than any tropical cyclone ever recorded on Earth.

An outline of the continental United States superimposed over the central cyclone and an outline of Texas is superimposed over the newest cyclone at Jupiter's south pole give a sense of their immense scale. The hexagonal arrangement of the cyclones is large enough to dwarf the Earth. (Credits: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM)

The discovery of this evolving meteorological phenomenon almost didn't happen as Jupiter itself almost caused the mission to end abruptly.

Juno is a solar-powered spacecraft that relies on constant light from the sun to keep the craft alive. Flying through Jupiter's enormous shadow would take about 12 hours to complete, which would cut off the power source, drain the spacecraft's battery and potentially spell the end of the mission.

"Our navigators and engineers told us a day of reckoning was coming, when we would go into Jupiter's shadow for about 12 hours," said Steve Levin, Juno project scientist at NASA's Jet Propulsion Laboratory.

To avoid the potential mission-ending eclipse, Juno fired up its engine (which was not initially designed for such a maneuver) and adjusted its trajectory just enough to avoid the icy grip of Jupiter's shadow.

Jupiter's moon Io casts its shadow on Jupiter whenever it passes in front of the Sun as seen from Jupiter. (NASA/JPL-Caltech/SwRI/MSSS Image processing by Tanya Oleksuik, © CC BY)

"Thanks to our navigators and engineers, we still have a mission," said Bolton. "What they did is more than just make our cyclone discovery possible; they made possible the new insights and revelations about Jupiter that lie ahead of us."

NASA scientists will continue to study these polar vortices in future flights over Jupiter's south pole to better understand the atmosphere over this part of the planet.

"These cyclones are new weather phenomena that have not been seen or predicted before," said Cheng Li, a Juno scientist from the University of California, Berkeley. "Nature is revealing new physics regarding fluid motions and how giant planet atmospheres work. Future Juno flybys will help us further refine our understanding by revealing how the cyclones evolve over time."