40-year study finds mysterious patterns in temperatures at Jupiter

Credit: ESO / L.N. Fletcher

An international team of scientists, including at the University of Leicester, have completed the longest-ever study tracking temperatures in Jupiter’s upper troposphere, the layer of the atmosphere where the giant planet’s weather occurs and where its signature colourful striped clouds form. The work, conducted over four decades by stitching together data from NASA spacecraft and ground-based telescope observations, found unexpected patterns in how temperatures of Jupiter’s belts and zones change over time. The study is a major step toward a better understanding of what drives weather at our solar system’s largest planet and eventually being able to forecast it. 

The study is based on an ERC Consolidator Grant awarded to Professor Leigh Fletcher at the University of Leicester, which funded work by a postdoctoral researcher. The purpose of the grant was to search for natural patterns of climate variability in the atmospheres of the four giant planets, to understand the phenomena shaping their banded, stormy atmospheres.  

Jupiter’s troposphere has a lot in common with Earth’s: It’s where clouds form and storms churn. To understand this weather activity, scientists need to study certain properties, including wind, pressure, humidity, and temperature. They have known since NASA’s Pioneer 10 and Pioneer 11 missions in the 1970s that, in general, colder temperatures are associated with Jupiter’s lighter and whiter bands (known as zones), while the darker brown-red bands (known as belts) are locations of warmer temperatures.

But there weren’t enough data sets to understand how temperatures vary over the long-term. The new research, published this week in Nature Astronomy, breaks ground by studying images of the bright infrared glow (invisible to the human eye) that rises from warmer regions of the atmosphere, directly measuring Jupiter’s temperatures above the colourful clouds. The scientists collected these images at regular intervals over three of Jupiter’s orbits around the Sun, each of which lasts 12 Earth years. 

The University of Leicester team were responsible for acquiring all the Very Large Telescope data (a subset of the final dataset used in the paper, alongside the Infrared Telescope Facility and Subaru), processing a large volume of the infrared data that went into this study, and determining the atmospheric temperatures by developing a model of Jupiter’s infrared spectrum.  The derived temperatures were then used to search for regular and cyclic variations over many years.

In the process, they found that Jupiter’s temperatures rise and fall following definite periods that aren’t tied to the seasons or any other cycles scientists know about. Because Jupiter has weak seasons – the planet is tilted on its axis only 3 degrees, compared to Earth’s jaunty 23.5 degrees – scientists didn’t expect to find temperatures on Jupiter varying in such regular cycles. 

The study also revealed a mysterious connection between temperature shifts in regions thousands of miles apart: As temperatures went up at specific latitudes in the northern hemisphere, they went down at the same latitudes in the southern hemisphere – like a mirror image across the equator. 

“That was the most surprising of all,” said Glenn Orton, senior research scientist at NASA’s Jet Propulsion Laboratory and lead author of the study. “We found a connection between how the temperatures varied at very distant latitudes. It’s similar to a phenomenon we see on Earth, where weather and climate patterns in one region can have a noticeable influence on weather elsewhere, with the patterns of variability seemingly ‘teleconnected’ across vast distances through the atmosphere.”

The next challenge is to find out what causes these cyclical and seemingly synchronized changes.  

“We’ve solved one part of the puzzle now, which is that the atmosphere shows these natural cycles,” said co-author Leigh Fletcher of the University of Leicester. “To understand what’s driving these patterns and why they occur on these particular timescales, we need to explore both above and below the cloudy layers.”

One possible explanation became apparent at the equator: The study authors found that temperature variations higher up, in the stratosphere, seemed to rise and fall in a pattern that is the opposite of how temperatures behave in the troposphere, suggesting changes in the stratosphere influence changes in the troposphere and vice versa.

Decades of observations 

Orton and his colleagues began the study in 1978. For the duration of their research, they would write proposals several times a year to win observation time on three large telescopes around the world: the Very Large Telescope in Chile as well as NASA’s Infrared Telescope Facility and the Subaru Telescope at the Maunakea Observatories in Hawaii. 

During the first two decades of the study, Orton and his teammates took turns traveling to those observatories, gathering the information on temperatures that would eventually allow them to connect the dots. (By the early 2000s, some of the telescope work could be done remotely.) 

Scientists hope the study will help them eventually be able to predict weather on Jupiter, now that they have a more detailed understanding of it. The research could contribute to climate modeling, with computer simulations of the temperature cycles and how they affect weather – not just for Jupiter, but for all giant planets across our solar system and beyond.

“Measuring these temperature changes and periods over time is a step toward ultimately having a full-on Jupiter weather forecast, if we can connect cause and effect in Jupiter’s atmosphere,” Fletcher said. “And the even bigger-picture question is if we can someday extend this to other giant planets to see if similar patterns show up.”