Astounding Sights at Saturn

When Cassini arrived at Saturn in 2004, the northern part of the planet was just emerging from winter and appeared blue.

Cassini watched as this region slowly changed color over the years, with the approach of summer.

Blues were replaced with subtle golden hues as hazes formed high in Saturn's atmosphere.

Cassini studied a giant, six-sided jet stream surrounding Saturn's north pole. Called the Hexagon, this unique feature is as wide as Earth on each of its sides.

At the center of the Hexagon, Cassini found a swirling, hurricane-like storm.

This vortex is 1,250 miles (2,000 kilometers) across, with clouds swirling around it as fast as 330 miles per hour (150 meters per second).

In 2010 and 2011, the spacecraft watched as an enormous, bright storm erupted from deep within the planet.

The storm grew until it encircled the whole planet, finally dying out after its head met its tail.

Earlier, upon arriving at Saturn, Cassini encountered the distant, outer moon Phoebe.

The mission's measurements determined this oddball object was captured by Saturn, but it originally came from somewhere much farther from the Sun.

Cassini also had several close flybys with the oddly shaped moon Hyperion.

The mission found the moon to be so under-dense that meteor impacts tend to either punch deep into its surface or blast material into space, never to return.

Cassini solved a several-hundred years old mystery in determining why one Saturn moon, called Iapetus, is bright on one side and dark on the other.

The mission found that Iapetus gets its peculiar appearance due to runaway migration of ice from one side.

Dust from the moon Phoebe settling onto the dark side's surface may be to blame for jumpstarting the process.

Among Cassini's greatest discoveries was that the small, icy moon Enceladus is geologically active. The moon was found to have long fractures near its south pole that erupt water vapor, icy particles, and simple organic materials.

The discovery shot Enceladus to the top of a short list of worlds that might have the right ingredients for life.

Cassini researchers determined this spray came from a global, underground ocean of salty liquid water.

They were even able to tell that there are likely hydrothermal vents on the seafloor, spewing out hot, mineral-right water.

Another of Cassini's most important targets for exploration, from the beginning, was Saturn's largest moon, Titan.

The planet-sized moon is shrouded in a thick haze that obscures its surface, so Cassini carried special cameras and a radar to peer through the haze.

Cassini also carried a passenger: the European Space Agency's Huygens probe. The probe landed on Titan in 2005.

As it continued its study of Titan from space, Cassini discovered that there are giant seas of liquid hydrocarbons on Titan's surface, especially near the north pole.

The spacecraft spotted sun glints, like the one shown here, that are telltale signs of a glassy smooth, liquid surface.

Cassini's radar pierced the haze to map the seas and much of the rest of Titan's surface.

Researchers even figured out a way to measure the depths of the seas by bouncing the radar beam of the sea floors.

In addition to the larger moons, Cassini also had many encounters with Saturn's smaller denizens.

The three moons seen here lurk near the outer edges of the rings. Cassini found that they each possess a band around their middle where ring particles have settled.

The smallest of the moons in the previous montage is named Daphnis. This little moon was discovered by Cassini, orbiting the planet within a gap in the rings that it creates with its own gravity.

Scientists also spotted swarms of moonlets in the rings that are smaller than Daphnis, and thus unable to open up permanent gaps of their own. These features are named "propellers" because they look something like the two bright lobes of an airplane propeller.

The closer Cassini peered at Saturn's rings, the farther their complex structure continued.

Scientists also found hints about the rings' composition, which they hope will help them understand how these fascinatingly complex structures formed.

In 2009, Saturn reached equinox, in which the Sun's rays shone edge-on to the rings.

During this brief period of a few weeks, Cassini witnessed myriad structures suddenly made visible, as the change in illumination caused them to cast shadows. Here, Cassini reveals fluffy mountains of ice particles in the edge of Saturn's B ring.

In 2017 Cassini's exploration of Saturn came to a thrilling end. After a series of first-ever plunges through the gap between Saturn and the rings, the spacecraft dove into the planet, returning scientific data about the atmosphere until its signal was lost.