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Neptune has been cooling down for nearly 20 years – when it should be doing the opposite

The most distant planet in our solar system entered its summer season two decades ago – but contrary to expectations it is cooling down. And the most surprising thing is that it is cooling down quite quickly.

Our knowledge of the most distant planet in our solar system is still scarce. Years last longer (one year on Neptune equals 165 on Earth) and changes tend to be observed more slowly. In the last two decades, Neptune the global temperature has dropped by 8 degrees Celsius – despite the planet having entered the summer season.

The international team of astronomers has tracked Neptune’s atmospheric temperatures for the past 17 years – and this sudden change is surprising. “This change was unexpected. As we’ve been observing Neptune during early summer in the south, we expect temperatures to warm slowly, not cool,” explains University of Leicester researcher Michael Roman.

And the surprise doesn’t stop there. Despite this global temperature drop on Neptune, between 2018 and 2020 there was a sudden 11ºC rise at the south pole. A warmer temperature in this region wouldn’t be surprising – Neptune’s hot polar vortex has been known since 2007 – but a rise of 11ºC in two years is unprecedented, especially on a planet where changes are expected to be slower.

As on our planet, Neptune also has seasons as it orbits the sun – with the difference that each season on Neptune lasts about 40 years. In the case of Neptune, it has been summer in the southern hemisphere since 2005, when researchers began tracking changes in atmospheric temperatures on the planet furthest from our solar system.

How complex can it be? In the case of planet Earth, the warnings of climate scientists are consensual in setting a limit on the increase in the planet’s temperature to 1.5ºC – since the industrial revolution, more than 150 years ago. The rise of 11ºC in two years, on a planet where the temperature was around -220ºC, is a huge surprise – and for which there is still no explanation.

How did it happen? We don`t know yet
To track atmospheric temperatures on Neptune, the team of astronomers used ground-based telescopes, including the European Southern Observatory’s VLT, to record these temperatures through thermal infrared images. Through the images collected, the team managed to build a picture of the temperature and its variations during this first part of its summer.

“The data we collected covers less than half of a season of the year on Neptune, so no one expected to see such significant and rapid changes,” says Glenn Orton, a researcher at the Jet Propulsion Laboratory at the University of Caltech (United States of America).

These unexpected measurements still have no justification for the team of scientists that presents them. There are, however, some hypotheses, such as the chemical change of Neptune’s stratosphere, the solar cycle, or even random weather patterns that we are not yet aware of.

“Neptune is in itself very intriguing to most of us because we still know so little about the planet. This points to a much more complicated picture of Neptune’s atmosphere and the way it changes over time.”

In the coming years, Neptune will continue to be a priority space for recording temperatures – and their variations -, mainly to understand what motivates these rapid and surprising changes in temperature.

Source: With Agencies

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