Neptune has undergone a large-scale climate change

The period of Neptune’s revolution is about 165 years; Thus each Neptune season lasts about forty years. The Southern Hemisphere has been in summer since 2005. An international team of astronomers set out to track the atmospheric temperatures of this giant planet, from 2003 to 2020, using several powerful ground-based telescopes, including very large telescope European Southern Observatory (ESO) equipped with the VISIR instrument (VLT and mid-infrared spectrometer). They have come to the end of their study and today present the findings from 17 years of observations. at Planetary Science Journal.

Amazing and unexpected temperature changes

Neptune orbits the Sun at a distance of about 4.5 billion km, which gives it a small apparent size than Earth; Moreover, it is an icy planet. So measuring its temperature from the ground was particularly difficult. ” This type of study is only possible with sensitive infrared images from large telescopes such as the VLT “,” Fletcher assures me, professor of planetary sciences at the University of Leicester and co-author of the study. Remember, the VLT has only been fully operational since 2001. The team also used data from NASA’s Spitzer Space Telescope, as well as images taken with the Gemini Observatory telescopes and the Subaru and Keck telescopes.

Astronomers have measured Neptune’s temperature using thermal imaging cameras, which measure infrared light emitted by astronomical objects. Observing the infrared radiation emitted from the stratosphere of Neptune made it possible to follow the evolution of its temperature. The team was able to collect about 100 images of the planet, taken over a 17-year period – which ultimately corresponds to less than half a season and scientists did not expect to observe climate changes of this magnitude.

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In the years around the 2005 southern summer solstice, images already revealed significant changes in mid-infrared emission. In particular, scientists found a sudden drop in global temperatures for Neptune between 2003 and 2009, followed by a significant warming in the Antarctic between 2018 and 2020. This change was unexpected. As we observed Neptune at the start of its southern summer, we expected temperatures to slowly rise, not cool. “,” Michael Roman explainsa postdoctoral associate fellow at the University of Leicester and lead author of the study.

” These observations provide the strongest evidence to date of this Processes produce global and sub-seasonal regional variations in the stratosphere of Neptune ‘,” conclude the researchers.

Still unknown cause

Despite the arrival of the Australian summer, the average global temperature for Neptune gradually decreased by 8 °C between 2003 and 2018. After that, the Antarctic temperature has risen dramatically over the past two years of observation: between 2018 and 2020, temperatures have risen Temperature by 11 degrees Celsius! The researchers noted that the South Pole brightened in stratospheric images between 2018 and 2020, while the middle and lower latitudes remained darker than in previous years.

The first three images (2006, 2009, 2018) were taken using the VLT’s VISIR instrument, while the 2020 image is from the Subaru Telescope’s COMICS instrument. After the planet’s gradual cooling, the Antarctic has warmed dramatically in recent years, as seen in the bright region below Neptune in images from 2018 and 2020. Credits: ESO/M. Roman, NAOJ/Subaru/Comics

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Scientists already knew that Neptune has a warm polar vortex. Because of the planet’s axial tilt, the south pole is exposed to the sun during the last quarter of the year of Neptune; Then as Neptune moves to the other side of the sun, this hot spot moves north. However, the researchers note that this is the first time such rapid polar warming has been observed on the planet.

These temperature changes were really unexpected and astronomers don’t yet know what could have caused such changes. Among the hypotheses raised: seasonal influence, random weather phenomena, or even solar activity. ” to meAs the new solar cycle begins to accelerate, regular observations over the next decade will be crucial to understanding the nature and trends that shape Neptune’s stratospheric variability. The team stands out.

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Other observations will already be necessary to crack all the mysteries of this planet. No probe has visited Neptune since the Voyager 2 mission in 1989; Fortunately, Hubble made it possible to collect some additional data. L ‘very large telescope From ESO – which is planned to start operation in 2027 – with its primary mirror measuring 39 meters in diameter (for comparison, the VLT consists of 4 telescopes with a height of 8 meters), it can observe temperature changes in more detail. The James Webb Telescope will provide valuable data on the chemistry of Neptune’s atmosphere.