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Scientists have discovered unexplained climate patterns on Jupiter that periodically repeat in years-long cycles, and weirdly mirror each other in each hemisphere. The strange finding raises intriguing questions about the biggest planet in our solar system, as well as giant gas worlds that orbit alien stars, reports a new study.
Jupiter is so humongous that it could contain 1,300 Earths, a size that makes it one of the brightest objects in the sky. Over the past few centuries, telescopes have revealed the mesmerizing tempests that swirl across the upper layers of its skies and visiting spacecraft have confirmed that Jupiter’s atmosphere is unimaginably complex.
Glenn Orton, a senior research scientist at NASA’s Jet Propulsion Laboratory and the California Institute of Technology, has been watching Jupiter since he was a kid with a backyard telescope.
In the 1990s, Orton and his colleagues spotted tantalizing signs of weird climate patterns on the planet, but the researchers needed a specific set of long-term infrared data in order to get a sense of the bigger picture.
Now, Orton and his colleagues have discovered “unexpected seasonal and non-seasonal periodicities,” along with other “associated puzzles,” in infrared observations of Jupiter that span 40 years, according to a study published on Monday in Nature Astronomy. The results suggest that a higher layer of Jupiter’s atmosphere, called the stratosphere, is heavily influencing temperatures at a lower level, known as the troposphere.
“Although…there were some earlier hints in the stratosphere, the types of things we’ve discovered include several things we never anticipated,” Orton told Motherboard in an email. “That was one of our first ‘wow’ moments.”
Over the course of his career, Orton has seen Jupiter come into sharper focus thanks to both ground-based telescopes and a succession of NASA space missions, starting with Pioneer 10 and 11, launched in 1972, through to the Juno orbiter, which is currently circling the planet. These images have offered brief glimpses of periodic patterns in temperatures in the troposphere that have intrigued Jupiter-watchers for decades.
“My thesis work at Caltech included analyzing a combination of Pioneer 10/11 and ground-based infrared observations,” Orton said. “There were a couple of differences between Pioneer 10 and 11 maps of Jupiter that were separated by several months. So I thought of using ground-based infrared instrumentation to continue to see if things continued to change. And they did, so I kept looking. And they were changing still with the Voyager infrared observations.”
Little snippets of odd behavior continued to be revealed by new missions and ground-based telescopes, such as NASA’s Infrared Telescope Facility (IRTF). To build a more comprehensive view of just what is going on in Jupiter’s skies, Orton’s team used imagery from IRTF, the Subaru Telescope in Hawaii, and the Very Large Telescope in Chile that covered 1978 to 2019.
The extended timeline showed that tropospheric temperatures on Jupiter varied periodically on timescales of four years, seven to nine years, and 10 to 14 years, for reasons that are not at all clear. Even stranger, these climatic rhythms appear to be “anticorrelated” in latitudes in each hemisphere of the gas giant, “deepening the mystery,” according to Orton.
“When temperatures at these latitudes in the north rise, the temperatures at these latitudes in the south fall and vice-versa,” he said. “So their variations are mirror images of each other.”
The researchers speculate that the variations might be caused by oscillations in the stratosphere that produce “teleconnected patterns of variability between the two hemispheres,” potentially similar to Earth’s southern El Niño and the North Atlantic oscillations, according to the study. Earth may also be a model for understanding the key role the stratosphere plays in tropospheric cycles, as sudden warming events on our planet can display this “top-down” dynamic.
“In general, we will be testing global climate models based on the same fundamental principles we use for the Earth’s atmosphere to the atmosphere of Jupiter,” Orton said. “In fact, some of that work has already started.”
In addition to examining these models, the team has continued collecting observations of Jupiter that might provide insights into the mysterious climate patterns they’ve discovered. Most recently, the researchers have used the Microwave Radiometer (MWR) instrument onboard Juno to explore how stratospheric and tropospheric variabilities correspond to phenomena deeper in Jupiter’s atmosphere.
These efforts may uncover the forces that are driving Jupiter’s turbulent climate, which would in turn help scientists understand giant planets, and failed stars called “brown dwarfs” that exist across the universe.
“Realistic global climate models for Jupiter must address the origins of these unexpected seasonal and non-seasonal periodicities on a virtually aseasonal gas giant in preparation for their eventual extension to a wider array of brown dwarfs and gas giant planets outside our solar system,” Orton and his colleagues concluded in the study.