When gazing at the heavenly bodies in the sky with our naked eyes, we see them changing their positions constantly, but rarely do they ever transform their appearance, twinkle and colour—at least never significantly enough for us to notice. Observing them using powerful telescopes, however, is a different ball game altogether.
Now, in a new, interesting and otherworldly observation (quite literally), NASA’s Hubble Space Telescope has captured the changing of the seasons on planet Saturn, signified by the transformation of its colour bands. This transition from summer to fall was witnessed in the northern hemisphere of the ringed planet over a span of three years—from 2018 to 2020.
“These small year-to-year changes in Saturn’s colour bands are fascinating,” said Amy Simon, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
“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. We expect big changes on a seasonal timescale, so this is showing the progression towards the next season.”
As per the Hubble data that shows these changes from 2018 to 2020, Saturn’s equator got 5 to 10 per cent brighter in this three-year period, with its winds also undergoing a slight change.
During 2004-2009, NASA’s Cassini spacecraft had measured the winds blowing around the equator at roughly 1,300 kilometres per hour. But in 2018, they had accelerated to 1,600 kilometres per hour, only to decrease back to the Cassini speeds in 2019 and 2020.
NASA does add, however, that these winds also vary with altitude, so the change in measured speeds could also possibly mean the clouds in 2018 were about 60 kilometres deeper than those measured during the Cassini mission.
Being the sixth planet from the Sun in our solar system, Saturn orbits our star at a distance of about 1.4 billion kilometres. Each of its trip around the Sun takes about 29 Earth years, making each season on Saturn more than seven Earth years long.
Similar to the Earth, Saturn also revolves around the Sun on a tilted axis, which alters the amount of sunlight each hemisphere receives during its revolution. This variation in solar energy is believed to be causing some of the observed atmospheric changes that are observed on this gas giant.
Similar changes in planetary appearance due to seasonal changes have also been observed on Earth, using NASA’s Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and instruments including the NASA/NOAA Visible Infrared Imaging Radiometer Suite and the Moderate Resolution Imaging Spectroradiometer.
Compressing data of two-decade-long changes on Earth into a captivating few minutes, this animation released in 2017 showed our planet ‘breathing’.
Gene Carl Feldman, an oceanographer at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, had described these changes as “incredibly evocative visualisations of our living planet,” while adding: “That’s the Earth, that is it breathing every single day, changing with the seasons, responding to the Sun, to the changing winds, ocean currents and temperatures.”
Meanwhile, the Hubble observations of Saturn's seasonal changes were recently published as a paper in the Planetary Science Journal earlier this month, and can be accessed here.
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