On Neptune, the 40-year-old summer is experiencing a cold wave

Given the distance from our star, about thirty times the Earth-Sun distance, scientists still know relatively little about Neptune, where this cooling is called ‘unexpected’.

With seasons lasting 40 years each, the planet Neptune must be spared from sudden climatic changes, and yet it has undergone a marked cooling since the start of the Australian summer 17 years ago, according to a study on Monday (April 11).

This change was unexpectednoted Michael Roman, an astronomer at the British University of Leicester, responsible for the study and 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, for which a year lasts about 165 Earth years.

The farthest planet from our star, about thirty times Earth-sun distance, glowed too dimly to be properly studied by older-generation telescopes. It was not until the Voyager 2 probe’s visit in 1989 that the first clear images of this other blue planet were taken. Since then, it has come under scrutiny, thanks in particular to the Hubble Space Telescope and the ESO Very Large Telescope (VLT) in Chile.

This ice giant, with a likely rocky heart shrouded in a solid-state mixture of water, ammonia and methane, has a very dynamic atmosphere, recalls the study published in The Planetary Science Journal. With the strongest winds recorded on any planet in the solar system, at more than 2,000 km/h. And a cloud system that can change its appearance in a few days. But until now we had little information about the temperature variations of the atmosphere, a mixture of hydrogen, helium and hydrocarbons. †Since we’ve been observing Neptune since the beginning of the southern summer, we expected the temperature to rise slowly, not colder. Michael Roman explained.

Changes in the chemistry of the stratosphere

While the Australian summer began in 2005 in the southern hemisphere, the star’s average temperature dropped about 8 degrees Celsius between 2003 and 2018, according to the study’s observations. A figure to compare with the average temperature of -200 degrees Celsius. And that explains the difficulty of measuring it from Earth. †This kind of research is only possible due to the sensitivity of the infrared images from large telescopes such as the VLT, which can clearly observe Neptune, and these resources have only been available for 20 years.said Prof. Leigh Fletcher, study co-author and astronomer at the University of Leicester.

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

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