Astronomers surprised by ‘dramatic warming’ at Neptune’s south pole

Neptune

Planetary temperature conundrums are not confined to Earth. Nobody foresaw the observed changes that occurred on Neptune between 2018 and 2020.
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An international team of astronomers have used ground-based telescopes, including the European Southern Observatory’s Very Large Telescope (ESO’s VLT), to track Neptune’s atmospheric temperatures over a 17-year period, Phys.org.

They found a surprising drop in Neptune’s global temperatures followed by a dramatic warming at its south pole.

“This change was unexpected,” says Michael Roman, a postdoctoral research associate at the University of Leicester, UK, and lead author of the study published today in The Planetary Science Journal. “Since we have been observing Neptune during its early southern summer, we expected temperatures to be slowly growing warmer, not colder.”

Like Earth, Neptune experiences seasons as it orbits the Sun. However, a Neptune season lasts around 40 years, with one Neptune year lasting 165 Earth years. It has been summertime in Neptune’s southern hemisphere since 2005, and the astronomers were eager to see how temperatures were changing following the southern summer solstice.

Astronomers looked at nearly 100 thermal-infrared images of Neptune, captured over a 17-year period, to piece together overall trends in the planet’s temperature in greater detail than ever before.

These data showed that, despite the onset of southern summer, most of the planet had gradually cooled over the last two decades. The globally averaged temperature of Neptune dropped by 8°C between 2003 and 2018.

The astronomers were then surprised to discover a dramatic warming of Neptune’s south pole during the last two years of their observations, when temperatures rapidly rose 11°C between 2018 and 2020. Although Neptune’s warm polar vortex has been known for many years, such rapid polar warming has never been previously observed on the planet.

“Our data cover less than half of a Neptune season, so no one was expecting to see large and rapid changes,” says co-author Glenn Orton, senior research scientist at Caltech’s Jet Propulsion Laboratory (JPL) in the US.
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Because Neptune’s temperature variations were so unexpected, the astronomers do not know yet what could have caused them. They could be due to changes in Neptune’s stratospheric chemistry, or random weather patterns, or even the solar cycle.

More observations will be needed over the coming years to explore the reasons for these fluctuations.

Full article here.