Focusing on Poseidon’s stratosphere – the relatively stable region of the atmosphere above the turbulent weather layer – researchers expected to find rising temperatures on the planet visible from Earth with the onset of summer in the southern hemisphere, a four-decade period. Instead, they found the temperatures to drop significantly.
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The study was based on more than 95 images of thermal infrared radiation – each ever taken – from 2003 to 2020 using ground-based telescopes in Hawaii and Chile, most notably the European Southern Observatory’s Very Large Telescope. It is the most complete estimate to date for the atmospheric temperatures of Poseidon. “The atmosphere seems more complicated than we naively assumed, which, unexpectedly, seems to be a general lesson that nature teaches scientists over and over again,” said Michael Roman, a postdoctoral researcher at the University of Leicester in England. lead author of the study, published Monday in the Planetary Science Journal
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The temperature of Poseidon’s stratosphere dropped by as much as 14 degrees Fahrenheit (8 degrees Celsius) to minus 179 F (minus 117 C) in the 17 years studied. In contrast, temperatures in Poseidon’s troposphere – the even colder layer of the weather – did not fluctuate significantly, reaching minus 370 F (minus 223 C). Poseidon is one of the least explored of the eight planets in the solar system, with its great distance making it difficult to study from Earth. NASA’s Voyager 2 is the only spacecraft to make a close visit, flying next to Poseidon in 1989. “I think Poseidon is very interesting to many of us because we still know so little about him,” Roman said. Its temperature changes were unevenly distributed, with local fluctuations. The southern tropics were cooled, then warmed and then cooled again. Temperatures in mid-latitudes initially remained stable before falling gradually. South Pole temperatures initially dropped only slightly before warming dramatically between 2018 and 2020.
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“I suspect that the overall drop in temperature may most likely be due to changes in atmospheric chemistry, which responds to changes in seasonal solar radiation and, in turn, changes how efficiently the atmosphere cools,” Roman said. The average diameter of Poseidon is about 30,600 miles (49,250 km), making it four times wider than Earth. It orbits more than 30 times farther from the Sun than the Earth at an average distance of about 2.8 billion miles (4.5 billion km), taking about 165 Earth years to complete a single orbit around the Sun – one year of Poseidon. The dwarf planet Pluto often orbits even farther away, but its oval orbit sometimes brings it closer to the sun than Poseidon. Neptune and neighboring Uranus are classified as ice giants, in contrast to the gas giants Jupiter and Saturn. Poseidon, which, like the other planets, does not have a solid surface, has an extremely dynamic atmosphere of mainly hydrogen and helium, with a small amount of methane, over a mantle mainly of ammonia and water mud and a solid core. Poseidon can be proud of the strongest winds on any planet. Neptune could offer lessons for planets beyond our solar system, called exoplanets, said study co-author Glenn Orton, a planetary scientist at Caltech’s Jet Propulsion Laboratory. “The close relationship that Poseidon can share with a large portion of the exoplanet population,” Orton said, “means it may be ‘an exoplanet in our backyard’ – probably at the coldest end of the spectrum, but it is still model for the things we could expect to see in the meteorology of various exoplanets. “ (Report by Will Dunham · Edited by Lisa Shumaker)
