Cassini Arrives at Saturn
Cassini arrived at Saturn in 2004, after a seven-year voyage. It was the first spacecraft to orbit the ringed planet.
Northern Winter
Like Earth, Saturn has a tilted axis. Cassini arrived in the depths of northern winter, with Saturn’s rings tipped up and its north pole in darkness.
A Hexagonal Storm
Cassini used infrared to view the hexagonal jet stream swirling around Saturn’s north pole, a six-sided vortex capped with a shimmering aurora.
The Light Returns
As spring approached and sunlight returned to Saturn’s north pole, Cassini studied the polar hexagon and the dark hurricane at its center.
Approaching Spring
Each season on Saturn lasts about seven Earth years. Cassini watched as Saturn’s rings slowly tipped downward, casting narrower and narrower shadows.
Saturn’s Spring Equinox
The shadows grew narrower until the spring equinox, when Saturn’s rings and equator were flat to the sun.
A Yearlong Storm
The change in seasons brought a huge storm that wrapped around Saturn’s northern hemisphere. Cassini detected lightning deep within the planet.
Titan
Mission scientists were particularly interested in Titan, Saturn’s largest moon — a hazy ball larger than the planet Mercury.
Cassini’s cameras were able to pierce Titan’s smoggy nitrogen atmosphere, revealing sunlight glinting on frigid lakes of liquid methane and other hydrocarbons.
Parachuting to Titan
Cassini released the Huygens probe to parachute through Titan’s atmosphere. As it descended, the probe recorded rivers and deltas carved by methane rain.
Moon Landing
Huygens sent back the first images from the surface of an alien moon.
Gravity Assist
Cassini returned to Titan over 100 times, using the large moon’s gravity to gradually shift the spacecraft’s orbit around Saturn.
Around the Rings
Cassini used Titan’s gravity to tour Saturn’s rings, climbing high above the ring plane and threading gaps between the rings.
Rainbows and Starlight
Cassini photographed the sun’s reflection and used background stars to measure the opacity of the rings.
Sixty-Two Moons
For 13 years, Cassini joined the intricate dance of Saturn’s 62 moons.
Enceladus
But of all of Saturn’s moons, Enceladus was the most surprising.
A Hidden Ocean
The icy crust of Enceladus encases an ocean of water, dotted with hydrothermal vents and warmed by the stretching and squeezing of Saturn’s gravity.
Geysers and Plumes
Cassini discovered geysers near the south pole of Enceladus, where plumes of water shoot into space and fall back as bright snow.
Inside the Plumes
Cassini flew through the plumes many times. The spacecraft’s instruments detected several molecules associated with life, but were not designed to search for microbes.
Could alien microbes be living inside Enceladus? It will take a future mission, and another spacecraft, to find the answer.
Rhea
Rhea, Saturn’s second-largest moon, is nearly 1,000 miles wide and pocked with craters.
Iapetus
Like Earth’s moon, Iapetus orbits with the same side facing its planet. The moon’s leading hemisphere sweeps its orbit clean of dark dust, giving Iapetus a two-toned appearance.
Dione
Cassini flew close by Dione four times, and it discovered evidence of another ocean of water under the moon’s wispy crust of ice.
Tethys
Tethys is mostly water ice, marked with a large crater on one side and a canyon running from pole to pole on the other.
Mimas
Mimas is one of the most battered moons in the solar system, bearing dents and dimples from ancient impacts.
Hyperion
Not all of Saturn’s moons are round. Hyperion is pockmarked and irregular, and tumbles chaotically in its orbit around the planet.
A Shared Orbit
The moons Janus and Epimetheus share the same orbit, slipping past each other every four years in an endless relay race.
Spiral Waves
When Janus and Epimetheus trade places, gravity forms a crest in Saturn’s B ring. Over decades, the crests form a spiral wave, a grooved record of past moon crossings.
Bright Spokes
Cassini studied the mysterious bright spokes, first seen by the Voyager spacecraft, that appear under the raking light of Saturn’s spring equinox.
Budding Moonlets
The spring light also helped Cassini find small clumps and moonlets casting shadows over the rings.
Clearing a Gap
The flattened moonlet Pan clears a path inside the rings, while Daphnis leaves a rippled wake where it passes.
Shepherd Moons
The moons Prometheus and Pandora straddle the narrow F ring, a thin band that is kinked and braided by the inner moon’s gravity.
Overlapping Planes
Some of Cassini’s most striking images were abstract — concentric rings with underlapping shadows.
Banded Saturn
Moons and rings cast crisp shadows across Saturn’s clouds.
Flattened at the Poles
When Cassini was level with the rings, Saturn’s oblate shape became clear. The planet is wider than it is tall.
Backlit by the Sun
Some of Cassini’s orbits took it behind Saturn, into hours of darkness.
Other Worlds Between the Rings
The spacecraft looked out toward the planet Uranus, a blue speck in the distance.
And Cassini turned back to find Earth through a gap in Saturn’s rings.
Last Images
Cassini took its final set of images on Thursday. The sequence included a brief glimpse of the moon Enceladus as it slipped behind Saturn.
Dive
After 22 passes inside the rings, Cassini plowed into Saturn’s rippled clouds on Friday. The spacecraft incinerated itself to prevent any future contamination of the moons Enceladus or Titan.
Burning Into Saturn
A short video about the end of the Cassini mission.