Neptune is seriously chilling out.
A recent analysis of nearly 20 years’ worth of thermal-infrared observations has revealed that the most distant planet in our solar system is unexpectedly cooling down—and scientists aren’t entirely sure why.
Like Earth, Neptune has an axial tilt that causes seasonal changes on the planet. But because the planet is so far away from the sun, its seasons are much longer than Earth’s. It takes Neptune 165 Earth-years to complete its orbit around the sun, meaning each season lasts roughly 40 years.
An international team of researchers looked at thermal infrared data collected by both Earth- and space-based observatories, including Chile’s European Southern Observatory’s Very Large Telescope and Gemini South telescope; Hawaii’s Subaru Telescope, Keck Telescope, and Gemini North telescope; as well as NASA’s Spitzer Space Telescope, which ended operations in January 2020.
That data, collected between 2003 and 2018, revealed a roughly 14-degree Fahrenheit decline in the temperature of Neptune’s stratosphere. Detectable temperature changes within the planet’s atmosphere during such a relatively short time period—almost half a season—were startling.
“This change was unexpected. Since we have been observing Neptune during its early southern summer, we would expect temperatures to be slowly growing warmer, not colder,” Michael Roman, an astrophysicist at Leicester University in the United Kingdom, and a co-author on the new paper published April 11 in Planetary Science Journal, said in a press statement.
Additionally, the team discovered that temperatures at the planet’s poles were changing, too. Specifically, over the span of two years (2018-2020), stratospheric temperatures at Neptune’s poles warmed by a staggering 20 degrees Fahrenheit—a startling discovery that researchers have never seen before.
More work is needed to parse out exactly what is causing these surprising temperature changes. The researchers suspect it may have something to do with the sun’s 11-year solar cycle or cyclical changes in the number of sun spots that it develops.
Next, the team hopes to analyze the planet and its mysterious atmosphere in closer detail using the James Webb Space Telescope, which will come online later this summer. The telescope—which was designed to prod the farthest reaches of the universe—will also help researchers who study some of our closest neighbors gain insight into their inner workings.