Based on observations over the past 17 years, scientists have identified a continuous drop in the planet’s temperature, which was suddenly interrupted by dramatic warming at its south pole. Thermal infrared images taken between 2003 and 2018 show the planet cooling by about eight degrees Celsius – until, at the end of this cycle, the temperature at its south pole rose by about 11 degrees Celsius. Poseidon’s atmosphere makes him a confused planet in many ways. A few years ago, scientists spotted a strange dark storm there that abruptly reversed its direction, something that had never been seen before. It is a very different planet from the inner gas giant of neighboring Uranus, which has no obvious weather patterns. “This change was unexpected,” said lead author Dr. Michael Roman, a postdoctoral fellow at the University of Leicester, about the new temperature discoveries. “Given that we observed Poseidon at the beginning of its southern summer, we expected that temperatures would rise slowly and not colder.” Neptune is about 17 times larger than Earth, but its distance from the sun and its axial inclination mean that a single year on Neptune lasts more than 165 years on Earth and its seasons last four decades each. The data collected by the team covered “less than half the period of Poseidon”, according to Dr. Glenn Orton, one of the study’s co-authors, “so no one expected to see big and rapid changes”. The cause of these unexpected temperature changes is currently unknown. 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 the 11-year cycle of solar activity can also have an effect,” he added. The 11-year solar cycle – which is characterized by periodic fluctuations in sun activity and sunspots – has long been suggested to affect the visible brightness of Poseidon. The new study, published in the Planetary Science Journal, reveals an experimental correlation between solar activity, stratospheric temperatures and the number of bright clouds seen in Poseidon.
