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.

A radar image of Ligeia Mare, a lake of liquid methane on Titan.

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.

Images taken in four directions as the Huygens probe parachuted through Titan’s atmosphere.

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.

Titan’s backlit atmosphere.

Titan and Rhea, Saturn’s largest moons.

Earth’s moon is larger than Rhea but smaller than Titan.

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.

The moonlet Atlas, only 19 miles across, follows the sharp edge of Saturn’s A ring.

The faint D ring, Saturn’s innermost ring.

The bright and narrow F ring.

The moon Epimetheus, barely visible at top center, casts a shadow across the A ring.

The dark Cassini Division separates Saturn’s A and B rings.

A detailed view of the B ring.

Rainbows and Starlight

Cassini photographed the sun’s reflection and used background stars to measure the opacity of the rings.

A rainbow effect from reflected sunlight.

Light from the star Antares filters through the rings.

Sixty-Two Moons

For 13 years, Cassini joined the intricate dance of Saturn’s 62 moons.

The moons Rhea and Epimetheus.

Clockwise from top: Telesto, Prometheus, Titan and Dione.

Glowing Titan and tiny Janus.

Rhea hovers above three distant moons.

From left: Dione, Prometheus and Tethys.

From left: Tethys, Enceladus and backlit Titan.

Enceladus

But of all of Saturn’s moons, Enceladus was the most surprising.

Enceladus on the ring plane.

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.

Geysers erupting during a Cassini flyby.

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.

Spray from Enceladus forms Saturn’s diffuse E ring.

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.

The cratered moon Rhea hovers over distant Dione.

Wispy terrain on Dione.

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.

Tethys appears ghostly white in ultraviolet light.

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.

Epimetheus

Janus

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.

Waves in Saturn’s B ring caused by the moon Janus.

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.

Faint spokes crossed by the long shadows of Janus and Mimas.

Budding Moonlets

The spring light also helped Cassini find small clumps and moonlets casting shadows over the rings.

A tiny moonlet embedded in dense rings.

Clearing a Gap

The flattened moonlet Pan clears a path inside the rings, while Daphnis leaves a rippled wake where it passes.

Pan

Pan circling within the Encke Gap in Saturn’s A ring.

Daphnis, the “wavemaker” moon.

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.

Prometheus and Pandora.

Kinks and twists in the F ring.

Prometheus carves a new ripple in the F ring.

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.

Crescent Saturn with flattened pole.

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