Like Earth, the light-blue ice giant Neptune in the outer solar system has distinct seasons: like our planet, it rotates around a tilted axis of rotation while it orbits the sun once every 165 years – which is why its planetary halves receive sunrays sometimes more, sometimes less steeply. Therefore, in summer on Neptune, the atmosphere becomes warmer than in winter. The seasons change slowly and last about 41 Earth years. But there are also significant temperature fluctuations on Neptune within a season, as a team of researchers has now summarized in the Planetary Science Journal after precise measurements.
The team analyzed infrared observations of Neptune collected over the past two decades by a variety of instruments, including ESO’s Very Large Telescope, various telescopes in Hawaii and the Spitzer Space Telescope. It was shown that the upper atmosphere of Neptune has cooled noticeably over a period of around 15 Earth years since 2003 – by a good eight degrees Celsius. That was unexpected, according to team member Michael Roman from the University of Leicester in a press release: The measurement data had been collected over the early summer of Neptune’s southern hemisphere, when the ice giant’s stratosphere should have been warmer.