On Neptune, the 40-year-old is facing a cold snap

With each season lasting for 40 years, Neptune must be spared abrupt climate changes, yet it has experienced remarkable cold since the start of its summer in Australia 17 years ago, according to a study on Monday (April 11).

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“This change was unexpectedMichael Roman, an astronomer at the British University of Leicester, responsible for the study, commented and was quoted in a press release from the European Southern Observatory (ESO). Scientists still know relatively little about Neptune, the eighth planet in the solar system, whose year spans about 165 Earth years.

The planet farthest from our star, about thirty times the distance between the Earth and the Sun, was glowing too faintly to be well studied by older generation telescopes. The first clear images of this other blue planet were obtained only after the visit of the Voyager 2 probe in 1989. Since then, it has been especially examined thanks to the Hubble Space Telescope and the Very Large Telescope (VLT) in Chile.

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This icy giant, whose core is potentially rocky and encased in a mixture of water, ammonia and methane in the solid state, has a very dynamic atmosphere, recalls the study published in The Planetary Science Journal. With the strongest winds ever recorded on a planet in the solar system, at more than 2,000 km/h. And a cloud system is able to change its appearance in a few days. But so far we have little information about changes in the temperature of the atmosphere, which is a mixture of hydrogen, helium and hydrocarbons. “Since we’ve been observing Neptune since the beginning of its southern summer, we expected temperatures to slowly rise, not get colder. Michael Roman explained.

Changes in stratospheric chemistry

While the Australian summer began in 2005 in the Southern Hemisphere, the star’s average temperature decreased by about 8 degrees Celsius between 2003 and 2018, according to the study’s observations. No. for comparison with the average temperature of -200°C. Which explains the difficulty of measuring it from the ground. “This type of study is only possible through the sensitivity of infrared images of large telescopes such as the VLT, which can clearly observe Neptune, and such means have only been available for twenty years.Professor Lee Fletcher, co-author of the study and an astronomer at the University of Leicester, explained.

Observations revealed another phenomenon, the sudden warming of the planet’s south pole, by about 11 degrees Celsius in 2018 and 2020. The measurements were made by studying infrared radiation emitted from the stratosphere, a layer of the atmosphere that lies above that which covers the surface. Scientists do not understand the reason for these temperature changes. They assume changes in stratospheric chemistry, random phenomena or even a connection to the solar cycle.

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