(ORDO NEWS) — An unprecedented analysis of Neptune’s temperature changes has shown that something rather strange is happening on the most distant planet in our solar system.
Distant Neptune, which revolves around the Sun at a distance of about 30 times the distance from Earth, completes its journey around the star in quite a long time: about 165 Earth years, which means that each season on Neptune lasts more than 40 Earth years.
Right now, Neptune’s southern hemisphere is in the midst of an epic four-decade-long summer, but for reasons scientists can’t fully explain, temperatures aren’t quite warming up – at least not as gradually as we might think.
A new study that compiles data from 17 years of observations of Neptune’s temperature suggests otherwise: The readings show a mysterious global average drop in temperature of about 8°C between 2003 and 2018, as evidenced by a significant drop in atmospheric radiation since 2003. of the year.
“This change was unexpected,” says planetary scientist Michael Roman from the University of Leicester in the UK.
“Because we observed Neptune at the beginning of the austral summer, we expected the temperature to gradually become warmer rather than colder.”
Collecting reliable data on the temperature of Neptune’s atmosphere is not an easy task, given how far this cold planet is from Earth.
Obtaining such data has only been possible since the beginning of the century, with the advent of sensitive infrared measurements on new space telescopes.
One of them is VISIR (VLT Imager and Spectrometer for mid-Infrared), installed on the European Southern Observatory’s (VLT) Very Large Telescope, which can determine temperature from the level of infrared radiation.
To study Neptune’s infrared emission, Roman and his team analyzed nearly 100 thermal observations of the planet, many from VISIR, as well as data from NASA‘s Spitzer Space Telescope and numerous ground-based telescopes in Chile and Hawaii.
The results – representing the largest collection of ground-based mid-infrared images of Neptune available to date – suggest that temperatures in Neptune’s stratosphere cooled (despite DST) for much of the period studied, although a late spike in emissions between 2018 and 2020 suggests that the atmosphere has warmed rapidly by about 11°C in just two years.
As to why the temperature of Neptune’s atmosphere fluctuates so unexpectedly in the middle of the season, we can’t be completely sure, but the researchers think that changes in the chemical composition of the atmosphere may be behind the observed fluctuations.
“While methane absorbs sunlight and warms the atmosphere, photochemically formed hydrocarbons – primarily ethane and acetylene – are powerful infrared emitters that serve to cool the stratosphere,” the researchers explain in their paper.
“The balance between radiative heating and cooling changes as the amount of photochemical hydrocarbons changes.”
Previous studies of Saturn’s temperature have shown that the interaction of chemicals in atmospheric clouds can influence their temperature, leading to temperature peaks before solar maximum, and it is possible that something similar is happening here.
“However, given Neptune’s 165-year orbital period, any seasonal changes are expected to occur gradually over decades,” the researchers wrote.
“The rapid changes observed between 2018 and 2020 seem surprisingly fast for a seasonal response… It appears that there are additional processes at work in Neptune’s atmosphere on sub-seasonal time scales, both regionally and globally.”
Another explanation could be weather variations – which can influence the composition and chemistry of atmospheric clouds, including the influence of the dark vortices seen on Neptune, which is another planetary mystery we’re still learning.
Solar flux is also worth considering, the researchers say, noting that changes in radiation caused by the solar activity cycle may somehow cause photochemical changes in Neptune’s atmosphere, which again could explain the temperature fluctuations we’ve observed.
All we know for sure is that we will need a lot of research to make sense of these amazing readings – this is just the latest mystery associated with this incomprehensible, distant world.
“I think Neptune itself is very intriguing to a lot of us because we still know so little about it,” says Roman.
“All of this points to a more complex picture of Neptune’s atmosphere and how it changes over time.”
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