Neptune, which orbits the sun 2.8 billion miles (4.5 billion kilometers) away, is experiencing Earth-like eras – just lasting much longer. A year on Poseidon lasts for about 165 earth years, so an era can last about 40 years. It has been summer in the southern hemisphere of Poseidon since 2005. Astronomers decided to monitor the planet’s atmospheric temperatures as soon as the southern summer solstice occurred that year. Nearly 100 thermal images of Poseidon taken since then showed that much of Poseidon gradually cooled, falling by 14 degrees Fahrenheit (8 degrees Celsius) between 2003 and 2018. A study of the phenomenon was published Monday in the Planetary Science Journal. “This change was unexpected,” study lead author Michael Roman, a postdoctoral fellow at the University of Leicester, said in a statement. “Given that we observed Poseidon at the beginning of its southern summer, we expected that temperatures would rise slowly and not colder.” Then a dramatic heating event occurred at the south pole of Poseidon between 2018 and 2020 and temperatures rose by 20 degrees Fahrenheit (11 degrees Celsius). This hot polar vortex completely reversed any cooling that had occurred before. This type of polar overheating has never been observed in Poseidon until now. “Our data cover less than half of Neptune, so no one expected to see big, rapid change,” study co-author Glenn Orton, a senior fellow at NASA’s Jet Propulsion Laboratory, said in a statement. The photos were taken using the European Southern Observatory’s Very Large Telescope and the Gemini South Telescope in Chile, along with Hawaii’s Subaru Telescope, Keck Telescope and Gemini North Telescope, as well as data from NASA’s most retired Spitzer Space Telescope. The infrared light emitted by Poseidon’s stratosphere, or the atmospheric band above the active layer of weather, helped astronomers detect temperature fluctuations. Frozen Neptune averages a negative 340 degrees Fahrenheit (negative 220 degrees Celsius) and astronomers still do not know what caused these temperature changes. At present, they believe that the unexpected changes may be due to several factors. “Temperature fluctuations may be related to seasonal changes in Poseidon’s atmospheric chemistry, which can change how efficiently the atmosphere cools,” Roman said. “But random variability in weather patterns or even a response to the 11-year cycle of solar activity can also have an effect.” More observations will be needed to really explore these possibilities. The James Webb Space Telescope will observe Uranus and Neptune later this year. The medium-sized infrared instrument of the space observatory can map the chemistry and temperatures in Poseidon’s atmosphere and could identify what caused the displacement. Neptune is more than 30 times farther from the sun than Earth, and is the only planet in our solar system that is not visible to the naked eye from Earth. So far, only NASA’s Voyager 2 spacecraft has flown close to Poseidon, something that happened in 1989. “I think Poseidon is himself very intriguing to many of us because we still know so little about him,” Roman said. “All this shows a more complex picture of Poseidon’s atmosphere and the way it changes over time.”
