Credit: [Credit must be given to the creator and the European Southern Observatory must be mentioned in the media article.] Credit: ESO / M. Roman, NAOJ / Subaru / COMICS An international team of astronomers used ground-based telescopes, including the European Southern Observatory’s Very Large Telescope (ESO’s VLT), to monitor Poseidon’s atmospheric temperatures over a 17-year period. They found a staggering drop in Poseidon’s global temperatures followed by a dramatic warming at its south pole. “This change was unexpected,” said Michael Roman, a postdoctoral fellow at the University of Leicester in the United Kingdom and lead author of the study, published today in The Planetary Science Journal. “Given that we observed Poseidon at the beginning of its southern summer, we expected that temperatures would rise slowly and not colder.” Like Earth, Poseidon experiences times as it orbits the Sun. However, a period of Poseidon lasts about 40 years, with a year of Poseidon lasting 165 earth years. It has been summer in the southern hemisphere of Poseidon since 2005, and astronomers were eager to see how temperatures changed after the southern summer solstice. Astronomers looked at nearly 100 thermal infrared images of Poseidon, taken over a period of 17 years, to combine global warming trends in greater detail than ever before. These data showed that, despite the onset of southern summer, most of the planet had gradually cooled over the past two decades. The global average temperature of Poseidon decreased by 8 ° C between 2003 and 2018. Astronomers were then surprised to discover a dramatic warming of Poseidon’s south pole in the last two years of their observations, when temperatures rose rapidly by 11 ° C between 2018 and 2020. Although Poseidon’s warm polar vortex is known here and for many years, such rapid polar warming has never been observed on the planet before. “Our data cover less than half of Neptune, so no one expected to see big, rapid change,” said co-author Glenn Orton, a senior fellow at Caltech’s Jet Propulsion Laboratory (JPL) in the United States. Astronomers measured Poseidon’s temperature using thermal cameras that measure the infrared light emitted by astronomical objects. For its analysis, the team combined all existing Poseidon images collected over the past two decades from ground-based telescopes. They studied the infrared light emitted by a layer of Poseidon’s atmosphere called the stratosphere. This allowed the team to create a picture of Poseidon’s temperature and fluctuations during part of his southern summer. Because Neptune is about 4.5 billion kilometers away and is very cold, the average temperature of the planet reaches about -220 ° C, measuring its temperature from Earth is not an easy task. “This type of study is only possible with sensitive infrared images from large telescopes such as the VLT that can observe Neptune clearly, and they have only been available for the last 20 years or so,” said co-author Leigh Fletcher, a professor at the University of Leicester. About one-third of all images taken came from the VLT Imager and Spectrometer for mid-InfraRed (VISIR) instrument at ESO’s VLT in the Atacama Desert, Chile. Due to the size and height of the telescope mirror, it has a very high resolution and data quality, offering the clearest images of Poseidon. The team also used data from NASA’s Spitzer Space Telescope and images taken with the Gemini South Telescope in Chile, as well as the Subaru Telescope, the Keck Telescope and the Gemini North Telescope, all in Hawaii. Because Poseidon’s temperature fluctuations were so unexpected, astronomers still do not know what could have caused them. They could be due to changes in Poseidon’s stratospheric chemistry, or to random weather patterns or even to the solar cycle. More observations will be needed in the coming years to investigate the reasons for these fluctuations. Future ground-based telescopes such as the ESO Ultra-Large Telescope (ELT) could observe temperature changes like these in more detail, while NASA / ESA / CSA’s James Webb Space Telescope will provide unprecedented new maps of chemistry and temperature in its atmosphere. Neptune. “I think Poseidon himself is very interesting to many of us because we still know so little about him,” says Roman. “All this shows a more complex picture of Poseidon’s atmosphere and how it changes over time.”

More information

This research was presented in the paper “Sub-seasonal fluctuations in the mean infrared emission of Poseidon” published today in The Planetary Science Journal (doi: 10.3847 / PSJ / ac5aa4). The team consists of MT Roman and LN Fletcher (School of Physics and Astronomy, University of Leicester, UK), GS Orton (Jet Propulsion Laboratory / California Institute of Technology, California, USA), TK Greathouse (Southwest Research Institute, San Antonio, Texas, USA), JI Moses (Space Science Institute, Boulder, CO, USA), N. Rowe-Gurney (Department of Physics and Astronomy, Howard University, Washington DC, USA; Astrochemistry Laboratory, NASA / GSFC, Greenbelt, MD, USA) · Center for Space Science and Technology Research and Exploration, NASA / GSFC, Greenbelt, MD, USA), PGJ Irwin (University of Oxford Atmospheric, Oceanic and Planetary Physics, Department of Physics Clarendon Laboratory, Oxford, UK Ant, UK) / EHU, Escuela Ingernieria de Bilbao, Spain), J. Sinclair (Jet Propulsion Laboratory / California Institute of Technology, California, USA), Y. Kasaba (Planetary and Atmospheric Research Center, University of Applied Sciences) , Japan), T. Fujiyoshi (Subaru Telescope, National Astronomical Observatory of Japan, HI, USA), I. de Pater (Department of Astronomy, University of California at Berkeley, CA, USA) and HB Hammel (Association of Universities for Research in Astronomy, Washington DC, USA). The European Southern Observatory (ESO) enables scientists around the world to discover the secrets of the Universe for the benefit of all. We design, build and operate world-class observatories – used by astronomers to address exciting questions and spread the fascination of astronomy – and promote international cooperation in astronomy. Established as an intergovernmental body in 1962, ESO is now supported by 16 Member States (Austria, Belgium, Czech Republic, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, the United Kingdom and Switzerland ), together with the host country of Chile and Australia as a strategic partner. ESO’s headquarters and visitor center and planetarium, ESO Supernova, are located near Munich, Germany, while the Atacama Desert in Chile, a wonderful place with unique sky-watching conditions, is home to our telescopes. ESO operates three observation sites: La Silla, Paranal and Chajnantor. At Paranal, ESO operates its Very Large Telescope and Very Large Telescope Symbolometer, as well as two research telescopes, the VISTA Infrared Operating System and the VLT Visible Light Telescope. The Paranal ESO will also host and operate the Cherenkov Telescope Array South, the largest and most sensitive gamma ray observatory in the world. Together with international partners, ESO operates APEX and ALMA in Chajnantor, two installations that observe the skies in millimeters and millimeters. At Cerro Armazones, near Paranal, we build “the world’s largest eye in the sky” – ESO’s extremely large telescope. From our offices in Santiago, Chile, we support our activities in the country and work with Chilean partners and society.

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Contacts

Michael RomanSchool of Physics and Astronomy, University of LeicesterLeicester, UKEmail: [email protected] Glenn OrtonCaltech’s Jet Propulsion Laboratory (JPL) Pasadena, California, USEmail: [email protected] Leigh FletcherSchool of Physics and Astronomy, University of LeicesterLeicester, UKTel: + 44 (0) 116 252 3585 Email: [email protected] Bárbara FerreiraESO Media ManagerGarching near Munich, GermanyTel: +49 89 3200 6670Cell: +49 151 241 664 0Email: [email protected]

Date of publication of the article

11-Apr-2022