Neptune just experienced an unexplained temperature shift

The most distant planet in the solar system has revealed a new mystery.

Astronomers who have been observing Neptune over the past 17 years using multiple ground-based telescopes, noticed a remarkable drop in the planet’s global temperature. This was then followed up by a dramatic warming trend towards the planet’s South Pole.

Neptune orbits the sun at a distance 2.8 billion miles (4.5 million kilometers), and experiences seasons just like Earth. They just last longer. A single season on Neptune can last 40 years. One year is roughly 165 Earthyears. Since 2005, summer has been in Neptune’s south hemisphere.

Astronomers determined that the planet’s atmospheric temperatures would be monitored once the southern summer solstice took place in that year.

Nearly 100 thermal images taken of Neptune since then have shown that Neptune has been cooling steadily, dropping by 14 degrees Fahrenheit (8° Celsius) between 2003-2018

A study on this phenomenon was published Monday in the Planetary Science Journal.

“This change was unexpected,”Michael Roman, a postdoctoral research associate from the University of Leicester, stated in a statement that he was the lead author of the study. “Since we have been observing Neptune during its early southern summer, we expected temperatures to be slowly growing warmer, not colder.”

Then, Neptune’s south Pole experienced a dramatic warming event between 2018 and 2020. Temperatures rose by 20 degrees Fahrenheit (11 Celsius). The warm polar vortex reversed all cooling.

This level of polar warming has not been seen on Neptune before now.

“Our data cover less than half of a Neptune season, so no one was expecting to see large and rapid changes,”Glenn Orton (senior research scientist at NASA’s Jet Propulsion Laboratory), was coauthor of the study and released a statement.

Images were taken using the European Southern Observatory’s Very Large Telescope (ESO’s Very Large Telescope) and Gemini South telescope (Chile), along with Hawaii’s Subaru Telescope, Keck Telescope, and the Gemini North telescope. Also, data from NASA’s now-retired Spitzer Space Telescope. Astronomers detected temperature fluctuations using infrared light from Neptune’s stratosphere.

Frosty Neptune’s average temperature is negative 340 degrees Fahrenheit (negative 220-degree Celsius). Astronomers are still trying to figure out what caused these temperature shifts.

They believe that unexpected changes may be caused by a number factors.

“Temperature variations may be related to seasonal changes in Neptune’s atmospheric chemistry, which can alter how effectively the atmosphere cools,”Roman said. “But random variability in weather patterns or even a response to the 11-year solar activity cycle may also have an effect.”

To fully explore these possibilities, more observations will be required. The James Webb Space Telescope will be observing Uranus, Neptune and other planets later in the year. The mid-infrared instrument in the space observatory’s space observatory can map Neptune’s atmosphere and determine what caused the shift.

Neptune is 30 times farther from the sun than Earth and is the only planet in the solar system that isn’t visible to the naked eye. Neptune has been seen up close by NASA’s Voyager 2 spacecraft only once, in 1989.

“I think Neptune is itself very intriguing to many of us because we still know so little about it,”Roman said. “This all points towards a more complicated picture of Neptune’s atmosphere and how it changes with time.”