Using Hubble to monitor changing seasons on Saturn

Three images of Saturn, taken in 2018, 2019 and 2020, show the transition from summer to fall in the northern hemisphere. Image: NASA/ESA/STScI/A. Simon/R. Roth

Astronomers are using the Hubble Space Telescope to monitor changes in the turbulent atmosphere of Saturn, capturing the transition from summer to fall in the northern hemisphere as seen in a series of images captured in 2018, 2019 and 2020.

“These small year-to-year changes in Saturn’s colour bands are fascinating,” said Amy Simon, planetary scientist at NASA’s Goddard Space Flight Center and lead author of a paper in the Planetary Science Journal. “As Saturn moves towards fall in its northern hemisphere, we see the polar and equatorial regions changing, but we are also seeing that the atmosphere varies on much shorter timescales.”

From 2018 to 2020, Saturn’s equator brightened by 5 to 10 percent and winds near the equator dropped from about 1,600 kilometres per hour (1,000 mph) to about 1,300 kph (800 mph) as observed by the Cassini spacecraft between 2004 and 2009. But the winds also vary with altitude, so it’s possible the change in measured velocity was the result of differing cloud heights

“What we found was a slight change from year-to-year in colour, possibly cloud height, and winds, not surprising that the changes aren’t huge, as we’re only looking at a small fraction of a Saturn year,” said Simon. “We expect big changes on a seasonal timescale, so this is showing the progression towards the next season.”

Saturn orbits the Sun at a distance of about 1.4 billion kilometres (886 million miles), taking 29 Earth years to complete one circuit. Seasons last more than seven years on Earth.