Saturn’s solstice — the longest day of summer in the northern hemisphere and the shortest day of winter in the southern hemisphere — arrived this month for the giant planet and its moons.
“During Cassini’s Solstice Mission, we have witnessed an entire season at Saturn,” said Cassini project scientist Dr. Linda Spilker, from NASA’s Jet Propulsion Laboratory.
“The Saturn system undergoes dramatic transitions from winter to summer, and thanks to Cassini, we had a ringside seat.”
The Saturnian solstice occurs about every 15 Earth years as the gas giant and its entourage slowly orbit the Sun, with the north and south hemispheres alternating their roles as the summer and winter poles.
Reaching the solstice, and observing seasonal changes in the Saturn system along the way, was a primary goal of Cassini’s Solstice Mission — the name of Cassini’s second extended mission.
Cassini arrived at Saturn in June 2004 for its four-year primary mission to study Saturn and its rings and moons.
Cassini’s first extended mission, from 2008 to 2010, was known as the Equinox Mission.
During that phase of the mission, Cassini watched as sunlight struck Saturn’s rings edge-on, casting shadows that revealed dramatic new ring structures.
NASA chose to grant the spacecraft an additional tour, the Solstice Mission, which began in 2010.
During the 7-year tour, Cassini watched a giant storm erupt and encircle the planet.
The orbiter also saw the disappearance of bluer hues that had lingered in the far north as springtime hazes began to form there.
The hazes are part of the reason why features in Saturn’s atmosphere are more muted in their appearance than those on Jupiter.
Data from the mission showed how the formation of Saturn’s hazes is related to the seasonally changing temperatures and chemical composition of Saturn’s upper atmosphere.
The Cassini researchers have found that some of the trace hydrocarbon compounds there — gases like ethane, propane and acetylene — react more quickly than others to the changing amount of sunlight over the course of Saturn’s year.
They were also surprised that the changes Cassini observed on Saturn didn’t occur gradually. They saw changes occur suddenly, at specific latitudes in Saturn’s banded atmosphere.
“Eventually a whole hemisphere undergoes change, but it gets there by these jumps at specific latitude bands at different times in the season,” said Cassini imaging team member Dr. Robert West, also from NASA’s Jet Propulsion Laboratory.
As Saturn’s solstice arrives, Cassini is currently in the Grand Finale phase, the final phase of its long mission.
Over the course of 22 weeks from April 26 to September 15, 2017, the spacecraft is making a series of dramatic dives between the planet and its icy rings.
The mission is returning new insights about the interior of the planet and the origins of the rings, along with images from closer to Saturn than ever before.
The mission will end with a final plunge into Saturn’s atmosphere on September 15.
This article is based on text provided by the National Aeronautics and Space Administration.