Images from the Webb Space Telescope show the end of Saturn’s northern summer as large planetary-scale winds change direction as autumn approaches.
The new observations also provide one last glimpse of Saturn’s north pole, with its enormous hot vortex filled with hydrocarbon gases, before the pole begins to retreat into darkness. in polar winter.
This report on the interplanetary period is due to new images analyzed by a team led by the University of Leicester and published in the Journal of Geophysical Research: Planets. They provide new insights into the changing seasons of the great outer planet, famous for its icy rings.
Like Earth, Saturn has an axial tilt and experiences the seasons in the same way. However, Saturn takes 30 years to orbit the Sun, so seasons last 7.5 years on Earth. Summer in the northern hemisphere of both worlds is coming to an end. While Earth is heading towards the northern autumnal equinox in September, Saturn is heading towards the northern autumnal equinox in 2025, which means that the north poles of both planets are heading into a long period of polar winter.
The Leicester team used the Webb Telescope’s MIRI instrument to study Saturn’s atmosphere in infrared light, allowing them to measure the temperature, gas abundance and cloud cover from the turbulent cloud tops to the upper atmosphere. part of the Earth. Atmosphere known as the stratosphere. The MIRI instrument splits infrared light into its component wavelengths, allowing scientists to see the fingerprints of the vast array of chemicals in the planet’s atmosphere.
In the image, created by combining just a few of the wavelengths observed by MIRI, the bright thermal emission from the north pole is highlighted in blue. At the north pole you can see the 1,500 km wide warm North Polar Cyclone (NPC), first observed by the Cassini mission. It is surrounded by a wider region of warm gases called the north pole stratospheric vortex (NPSV), which forms in Saturn’s spring and continues throughout the northern summer.
These are warm plumes high in the stratosphere, heated by the sun’s heat during Saturn’s long summer season. As the autumnal equinox approaches in 2025, the north polar stratospheric vortex will begin to cool and dissipate as the northern hemisphere retreats into autumn darkness.
By modeling the mid-infrared spectra, the scientists noted that the distributions of stratospheric temperatures and gases at this particular point in Saturn’s seasonal cycle were very different from those observed by Cassini during the northern winter and spring.
Saturn has a large stratospheric circulation pattern with warmer temperatures and excess hydrocarbons, such as ethane and acetylene, in the northern midlatitudes in winter, which means hydrocarbon-rich air sinks from the surface. Winds are believed to rise in the midlatitudes in the summer in the south, cross the equator, and sink in the midlatitudes in the winter in the north.
Results from the MIRI Medium Resolution Spectrometer taken in November 2022 reveal that this stratospheric circulation has now returned and cold stratospheric temperatures and low hydrocarbon abundance are observed in the north, between 10oN and 40oN, suggesting an increase in bad air to hydrocarbons in summer. , which flows towards the south.
Professor Leigh Fletcher, from the University of Leicester’s School of Physics and Astronomy, said in a statement: “The quality of the new JWST data is simple: in a short set of observations, we were able to continue the Mission legacy. . Cassini to a new Saturnian station, observing how weather patterns and atmospheric circulation respond to changes in sunlight.”
