Neptune temperature fluctuations baffle scientists: 'This was unexpected'
Thursday, 14 April 2022
Neptune the planet is an ice giant.
But new research by scientists with infrared technology has found its temperatures (which currently average a bone chilling -220C) are actually fluctuating wildly, and in ways we simply can't explain yet.
Astronomers observing Neptune for the past 17 years with ground-based telescopes tracked a surprising drop in its global temperatures and then a massive warming event.
Neptune orbits the sun at a distance of 4.5 billion kilometres and experiences seasons like Earth does – but they're not at all like ours.
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One year on Neptune lasts for about 165 Earth years, so a single season can last around 40 years. It's been summer in Neptune's southern hemisphere since 2005.
Astronomers and space scientists at the University of Leicester decided to track the planet's atmospheric temperatures once the southern summer solstice occurred that year.
Nearly 100 thermal images of Neptune taken since then showed that much of Neptune gradually cooled by 8C between 2003 and 2018.
A study on the phenomenon published on Tuesday (NZ time) in the Planetary Science Journal.
“This change was unexpected,” said lead study author Michael Roman, a postdoctoral research associate at the university.
“Since we have been observing Neptune during its early southern summer, we expected temperatures to be slowly growing warmer, not colder.”
Perhaps even more strangely, a dramatic warming event occurred at Neptune's south pole between 2018 and 2020 with temperatures rising by 11C.
This kind of polar warming has never been seen on Neptune until now.
“Our data cover less than half of a Neptune season, so no one was expecting to see large and rapid changes,” said study co-author Glenn Orton, senior research scientist at Nasa's Jet Propulsion Laboratory.
Images were taken using the European Southern Observatory's Very Large Telescope and Gemini South telescope in Chile, along with Hawaii's Subaru Telescope, Keck Telescope and the Gemini North telescope, as well as data from Nasa's now-retired Spitzer Space Telescope.
There are several unconfirmed theories for the temperature swerves.
“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.
“I think Neptune is itself very intriguing to many of us because we still know so little about it.”