Seasons on Neptune
Neptune, far out on the edge of our solar system, deserves to be called an "ice giant." Now the planet is actually getting cooler overall - in early summer. The cause is unclear.
The light blue ice giant Neptune in the outer solar system has distinct seasons like Earth: Like our planet The light blue ice giant Neptune in the outer solar system has distinct seasons like Earth: Like our planet, it rotates about a tilted axis of rotation as it orbits the Sun once in 165 years - which is why its planetary halves sometimes get solar rays 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 also on Neptune there are clear temperature fluctuations within a season, as a team of researchers summarizes now after exact measurements in the technical periodical "Planetary Science journal".
The team had evaluated observation data of Neptune in the infrared wavelength range, which were collected in the past two decades by different instruments, among other things by the Very Large Telescope of the ESO, different telescopes on Hawaii and the Spitzer space telescope. The results showed that Neptune's upper atmosphere has cooled noticeably over about 15 Earth years since 2003 - by a good eight degrees Celsius. That was unexpected, team member Michael Roman of the University of Leicester said 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 getting rather warmer.
In addition to the unexpected long-term trend, significant short-term fluctuations in temperature are also noticeable. For example, at Neptune's South Pole, where the uppermost atmosphere became about eleven degrees warmer between 2018 and 2020, bucking the trend. Although it has long been known that it is warmer at the ice giant's south pole, Neptune researchers had never observed such a temperature jump before. The cause is mysterious. The chemical composition of the stratosphere may have changed, says Roman, so that it can radiate more heat locally.
But it is also conceivable that the sun's activity cycle plays a role. It is possible that more or less bright clouds form in the atmosphere of the blue ice giant in the course of stronger or weaker solar activity, which could then change the temperature of the stratosphere. However, this connection must first be confirmed by further observations, say the researchers. Instruments from the newly commissioned James Webb Space Telescope, which is scheduled to turn its attention to the planets Neptune and Uranus in the course of 2022, should be helpful in this regard. In addition, the solar system researchers continue to hope that in the near future another probe will set off for the ice giants at the edge of the solar system.
Spectrum of Science
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