Poseidon is cooler than we thought
New research led by space scientists at the University of Leicester has revealed how temperatures in Poseidon’s atmosphere have fluctuated unexpectedly over the past two decades. The study, published today (Monday, April 11, 2022) in the Planetary Science Journal, used observations at thermal infrared wavelengths beyond the visible light spectrum to effectively detect the heat emitted by the planet’s atmosphere. An international team of researchers, including scientists from Leicester and NASA’s Jet Propulsion Laboratory (JPL), combined all of Poseidon’s existing thermal infrared images collected from multiple observatories over nearly two decades. These include the European Southern Observatory’s Very Large Telescope and the Gemini South Telescope in Chile, along with the Subaru Telescope, the Keck Telescope and the Gemini North Telescope, all in Hawaii, and spectra from NASA’s Spitzer Space Telescope. Neptune as seen in visible light (center) and thermal infrared (right) in 2020. The center image combines many images from the Hubble Space Telescope, while the thermal infrared image on the right was taken by the Subaru Telescope in Maunakea , Hawaii. In thermal infrared, Poseidon’s warm south pole shines brighter than ever. Credits: Michael Roman / NASA / ESA / STSci / MH Wong / LA Sromovsky / PM Fry Analyzing the data, the researchers were able to reveal a more complete picture of Poseidon’s temperature trends than ever before. But to the researchers’ surprise, these collective data sets show a decrease in Poseidon’s thermal luminosity since reliable thermal imaging began in 2003, indicating that global average temperatures in Poseidon’s stratosphere – the layer of the atmosphere just above the active layer of the weather – have decreased by about 8 degrees Celsius (14 degrees Fahrenheit) between 2003 and 2018. Dr. Michael Roman, Postdoctoral Research Fellow at the University of Leicester and lead author of the paper, said: “It simply came to our notice then. “Given that we observe Poseidon at the beginning of its southern summer, we would expect that the temperatures will rise slowly and not colder”. Poseidon has an axial inclination and thus experiences seasons, just like the Earth. However, given its great distance from the Sun, Poseidon takes over 165 years to complete an orbit around its host star, so its seasons change slowly, lasting more than 40 Earth years each. Dr. Glenn Orton, Senior Research Fellow at JPL and co-author of the study, noted: “Our data cover less than half of Poseidon’s era, so no one expected to see big and rapid changes.” View from Poseidon’s Voyager 2, recorded in August 1989. Credits: NASA / JPL-Caltech / Kevin M. Gill However, at the south pole of Poseidon, the data reveal a different and surprisingly dramatic change. A combination of observations from Gemini North in 2019 and Subaru in 2020 reveals that Poseidon’s polar stratosphere warmed by about 11 ° C (~ 20 ° F) between 2018 and 2020, reversing the previous cooling trend on average worldwide. Such polar heating has never been observed before in Poseidon. The cause of these unexpected changes in stratospheric temperature is currently unknown, and the results challenge scientists’ understanding of Poseidon’s atmospheric variability. Dr. Roman continued: “Temperature fluctuations may be related to seasonal changes in Poseidon’s atmospheric chemistry, which can change how efficiently the atmosphere cools. “But random variability in weather patterns or even a response to an 11-year cycle of solar activity can also have an effect.” The 11-year solar cycle (characterized by periodic fluctuations in solar activity and sunspots) has been suggested in the past to affect Poseidon’s visible brightness, and a new study reveals a possible but experimental correlation between solar activity and its temperatures. stratosphere and the number of luminous clouds seen in Poseidon. Subsequent temperature and cloud observations are required to further evaluate any possible connection in the coming years. Answers to these mysteries and more will be provided by the James Webb Space Telescope (JWST), which will observe both ice giants Uranus and Poseidon later this year. Leigh Fletcher, Professor of Planetary Science at the University of Leicester, will lead such observations with the allotted time of the JWST instrument series. Professor Fletcher, also co-author of this study, said: “The extreme sensitivity of the space telescope’s medium-infrared instrument, MIRI, will provide unprecedented new maps of Poseidon’s atmosphere chemistry and temperature, helping to better understand the nature of these recent changes.” Reference: “Sub-seasonal variant in the mean infrared emission of Poseidon” April 11, 2022, Planetary Science Journal.DOI: 10.3847 / PSJ / ac5aa4 This study was funded by a grant from the European Research Council to the University of Leicester, known as GIANTCLIMES. This work has previously discovered long-term changes in atmospheric temperatures and clouds in the gas giants Jupiter and Saturn, and provided the first maps of Uranus’ stratospheric temperatures. GIANTCLIMES paved the way for new discoveries on all four giant planets by JWST in the years to come. Additional co-authors of this work are Thomas Greathouse (Southwest Research Institute), Julianne Moses (Space Science Institute), Naomi Rowe-Gurney (Howard University / NASA Goddard Space Flight Center), Patrick Irwin (Oxford), Arrate Antuñano ( UPV / EHU), James Sinclair (JPL), Yasumasa Kasaba (University of Tohoku), Takuya Fujiyoshi (Subaru Telescope), Imke de Pater (UC Berkeley) and Heidi Hammel (Association of Universities for Research in Astronomy).
