Neptune is slowly cooling, but the cause is unknown

Astronomers studying Neptune's atmosphere discoveredSubseasonal Variation in Neptune's Mid-infrared Emission / The Planetary Science Journalthat the global temperature of the planet has decreased over the past 17 years, while the south pole has warmed significantly. The changes are captured in nearly 100 thermal infrared images taken between 2003 and 2020 by several ground-based telescopes.

At the same time, in the southern hemisphere of Neptune, summer began in 2005. The local year lasts about 165 Earth years, so the seasons on the planet also change less often: on Earth, 40 years have time to pass. But instead of summer warming from 2003 to 2018, the planet cooled by 8°C.

Without filters, Neptune looks as blue as ever (due to the fact that methane in the planet's upper atmosphere reflects light). But in infrared light, Neptune's south pole is noticeably brighter than the rest of the surface, indicating a warmer temperature. At the same time, at the beginning of summer, the heating was uniform.

Normally, the planet's average temperature is -220°C, but over the past two years of research, it has been found that the temperature of the pole has risen from -121°C to -110°C. At the same time, the zone near the equator had time to noticeably cool down, which can be seen from the darker color in infrared radiation.

Researchers aren't sure what could cause such a temperature difference between Neptune's poles and more central regions. It is noted that the observations could be affected by weather conditions. It is also assumed that changes in the chemical composition of the planet's stratosphere could cause a change in temperature.

Now scientists continue to observe and hope that new ground-based telescopes will be useful in observing the second half of the summer on Neptune.