NASA has released a spectacular set of images captured by the Hubble Space Telescope that show the seasons changing on Saturn—the second largest planet in the solar system.
The photographs, captured in 2018, 2019 and 2020, provide a glimpse of Saturn's northern hemisphere transitioning from summer to fall.
Just like Earth, Saturn experiences seasons because it is tilted relative to the plane of its orbit around the sun. This means that for half of Saturn's orbit, one hemisphere is tilted further toward the sun receiving more radiation, while the other is tilted away, receiving less.
Because Saturn is much further from the sun than our planet, it takes around 29 Earth years for the gas giant to orbit the star, meaning its seasons are far longer than ours. In fact, each season on Saturn lasts for more than seven Earth years.
The Saturn images were taken as part of Hubble's Outer Planets Atmospheres Legacy (OPAL) program, in which scientists have been conducting observations of the outer planets every year to see how they change with time.
Scientists have analyzed Hubble observations of Saturn conducted as part of OPAL between 2018-2020 for a study published this month in The Planetary Science Journal.
The Hubble data shows that in this period, the planet's equator became 5-10 percent brighter. Researchers also noticed small midsummer changes at the north pole, with a thin blue feature near the polar hexagon's outer edge disappearing between 2019 and 2020 and increasingly reddish polar haze.
Scientists also noted slight changes in wind speeds near the equator. Wind speeds in 2018 were found to be around 1,000 miles per hour—higher than during the period 2004-2019 when NASA's Cassini spacecraft clocked them at about 800 miles per hour.
But the Hubble data shows that in 2019 and 2020, wind speeds had decreased back to around 800 miles per hour.
Because Saturn's winds also vary with altitude, the change in measured speeds could also mean that the clouds in 2018 were around 37 miles deeper than than those measured by Cassini. The images also show slight variations in Saturn's colored bands from year-to-year.
"These small year-to-year changes in Saturn's color bands are fascinating," Amy Simon, planetary scientist at NASA's Goddard Space Flight Center and an author of the paper said in a statement.
"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," Simon said.
"What we found was a slight change from year-to-year in color, 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," Simon said. "We expect big changes on a seasonal timescale, so this is showing the progression towards the next season."
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