The Hubble Space Telescope is giving astronomers a glimpse of changes in Saturn’s vast and turbulent atmosphere as summer to fall transitions in the northern hemisphere in 2018, 2019, and 2020. The results of the study are published by the Planetary Science Journal.
Scientists have noted small annual variations in Saturn’s color bands. As the planet moves into fall in its northern hemisphere, the polar and equatorial regions are changing. In addition, the atmosphere changes on much shorter time scales.
The slight color change from year to year is possibly related to the height of the clouds and winds. Unsurprisingly, the changes are not huge, since only a small fraction of the year of Saturn is available for observation, the study authors note.
Hubble telescope data show that the equator became 5-10% brighter from 2018 to 2020, and the winds changed slightly. In 2018, the wind speed measured near the equator was around 1,600 kilometers per hour. These wind figures are higher than those measured by NASA’s Cassini spacecraft in 2004-2009. Then the wind speed was about 1300 kilometers per hour. In 2019 and 2020, they returned to their previous indicators. Saturn’s winds also change with altitude. The change in their velocities could mean that the clouds in 2018 were about 60 kilometers deeper than those measured during the Cassini mission. Further observations are needed to understand what is happening, NASA notes.
Saturn is the sixth planet in the solar system and orbits about 1.4 billion kilometers from the star. For the planet to orbit around it, it takes about 29 Earth years. As a result, each season on Saturn lasts more than seven Earth years. The Earth is tilted with respect to the Sun, which changes the amount of sunlight received by each hemisphere as the planet moves in its orbit. These fluctuations in solar energy are the driving force behind our seasonal changes. Saturn is also tilted, so as the seasons change in this distant world, changing sunlight is causing some of the observed atmospheric changes.
Like Jupiter, the largest planet in the solar system, Saturn is a gas giant made up mostly of hydrogen and helium, although there may be a rocky core deep inside. Huge storms, some the size of the Earth, erupt from time to time from the depths of the atmosphere. Since many of the planets found around other stars are also gas giants, astronomers are keen to learn more about how the atmospheres of gas giants work.