NASA's unmanned Cassini spacecraft, launched on October 15, 1997, was the fourth space probe sent to Saturn and the first to enter its orbit, studying the sixth planet from the sun since 2004. The probe continued to send back stunning images as well as important data right up until the end, when it made a planned descent and burned up in Saturn's atmosphere on September 15, 2017.
In this photo, a softly hued Saturn is embraced by the shadows of its rings. The gas planet's subtle northward gradation from gold to azure is a striking visual effect that scientists don't fully understand. A current theory is that it may be related to seasonal influences, tied to the cold temperatures in the northern (winter) hemisphere.
Images taken with blue, green and red spectral filters were used to create this color view, which approximates the scene as it would appear to the human eye.
This image of Saturn's rings was one of the final images Cassini sent back to Earth. It was captured on September 14, 2017, the day before Cassini's fiery demise.
Saturn and Enceladus
Saturn's moon Enceladus sinks behind the giant planet as NASA's Cassini spacecraft makes its final approach before burning up in Saturn's atmosphere. This view of Enceladus was taken by Cassini on September 13, 2017. It is among the last images Cassini sent back.
It's difficult to get a sense of scale when viewing Saturn's rings, but the Cassini Division (seen here between the bright B ring and dimmer A ring) is almost as wide as the planet Mercury.
The 2,980-mile-wide (4,800-kilometer-wide) division in Saturn's rings is thought to be caused by the moon Mimas.
Three of Saturn's moons -- Tethys, Enceladus and Mimas -- can be seen Cassini spacecraft photo released by NASA, February 22, 2016.
Tethys (660 miles or 1,062 kilometers across) appears above the rings, while Enceladus (313 miles or 504 kilometers across) sits just below center. Mimas (246 miles or 396 kilometers across) hangs below and to the left of Enceladus.
From afar, Saturn's rings look like a solid, homogenous disk of material, in this image from January 8, 2015. But upon closer examination from Cassini, the varied structures in the rings at almost every scale imaginable are apparent.
Structures in the rings can be caused by many things, but often times Saturn's many moons are the culprits.
Saturn and Dione
This image was taken in a wavelength that is absorbed by methane, May 27, 2015. Dark areas seen here on Saturn are regions with thicker clouds, where light has to travel through more methane on its way into and back out of the atmosphere.
Since Dione (698 miles or 1,123 kilometers across) doesn't have an atmosphere rich in methane the way Saturn does, it does not experience similar absorption -- the sunlight simply bounces off its icy surface.
Enceladus's water vapor jets, emitted from the southern polar region.
Tethys and Rhea moons
Tethys appears to be peeking out from behind Rhea, April 20, 2012.
Saturn's moon Enceladus
The tortured surface of Saturn's moon Enceladus and its fascinating ongoing geologic activity tell the story of the ancient and present struggles of one tiny world.
The enhanced color view of Enceladus seen here is largely of the southern hemisphere and includes the south polar terrain at the bottom of the image.
The image mosaic was created from 21 false-color frames taken on March 9 and July 14, 2005.
The three moons shown here -- Titan (3,200 miles or 5,150 kilometers across), Mimas (246 miles or 396 kilometers across), and Rhea (949 miles or 1,527 kilometers across) -- show marked contrasts, March 25, 2015.
Titan, the largest moon in this image, appears fuzzy because only its cloud layers are seen. And because Titan's atmosphere refracts light around the moon, its crescent "wraps" just a little further around the moon than it would on an airless body. Rhea (upper left) appears rough because its icy surface is heavily cratered. And a close inspection of Mimas (center bottom), though difficult to see at this scale, shows surface irregularities due to its own violent history.
Saturn's auroral emissions
The Cassini spacecraft obtained these images of Saturn's auroral emissions, which are similar to Earth's Northern Lights, June 21, 2005. These are the first images from the mission to capture the entire "oval" of the auroral emissions at Saturn's south pole.
In the side-by-side, false-color images, blue represents aurora emissions from hydrogen gas, while red-orange represents reflected sunlight. The photos show that the aurora lights at the polar regions respond rapidly to changes in the solar wind.
Earth seen between Saturn's rings
This view from NASA's Cassini spacecraft shows planet Earth as a point of light between the icy rings of Saturn.
The spacecraft captured the view on April 12, 2017, when Cassini was 870 million miles (1.4 billion kilometers) away from Earth.
"Hurricane" on Saturn
NASA's Cassini spacecraft grabbed this raw image of a "giant hurricane" in Saturn's atmosphere during its first dive between Saturn and its rings on April 26, 2017.
A stunning false-color view of Saturn's moon Hyperion reveals crisp details across the strange, tumbling moon's surface. Differences in color could represent differences in the composition of surface materials. The view was obtained during Cassini's close flyby on September 26, 2005.
Hyperion has a notably reddish tint when viewed in natural color. The red color was toned down in this false-color view, and the other hues were enhanced, in order to make more subtle color variations across Hyperion's surface more apparent.
Tethys and Mimas
Saturn is circled by its rings (seen nearly edge-on in this image), as well as by the moons Tethys (the large bright body near the lower right hand corner of this image) and Mimas (seen as a slight crescent against Saturn's disk above the rings, at about 4 o'clock). The shadows of the rings, each ringlet delicately recorded across Saturn's face, also circle around Saturn's south pole.
The image was taken in visible light with the Cassini spacecraft wide-angle camera on August 14, 2014.
Like a drop of dew hanging on a leaf, Tethys appears to be stuck to the A and F rings from this perspective, July 14, 2014. Tethys (660 miles, or 1,062 kilometers across) is composed primarily of ice.
Saturn's moon Iapetus
This near-true color view from Cassini reveals the colorful and intriguing surface of Saturn's moon Iapetus in unrivaled clarity, January 7, 2005.
During its historic close encounter with Phoebe, the Cassini spacecraft captured a series of high resolution images of the small moon, six of which have been put together to create this mosaic, June 23, 2004.
This specially processed composite view reveals a tremendous amount of structure in the northern polar atmosphere of Titan. The hazes in Titan's atmosphere are known to extend hundreds of kilometers above the surface.
Ten images taken on January 18, 2006, during a brief period, were processed to enhance fine detail and then were combined to create this view.
A mosaic of nine processed images acquired during Cassini's first very close flyby of Saturn's moon Titan on October 26, 2004, constitutes the most detailed full-disc view of the mysterious moon.
The images that comprise the mosaic have been processed to reduce the effects of the atmosphere and to sharpen surface features.
Wide-angle view of Saturn
The globe of Saturn, seen here in natural color, is reminiscent of a holiday ornament in this wide-angle view from NASA's Cassini spacecraft, July 22, 2013.
The characteristic hexagonal shape of Saturn's northern jet stream, somewhat yellow here, is visible. At the pole lies a Saturnian version of a high-speed hurricane, eye and all.
Titan and Rhea
Saturn's largest and second largest moons, Titan and Rhea, appear to be stacked on top of each other in this true-color scene from NASA's Cassini spacecraft, on June 16, 2011.
Saturn's southern hemisphere
With winter approaching in the southern hemisphere of Saturn comes the familiar blue hue of the planet's cold season, July 29, 2013.
Saturn and Titan
Slipping into shadow, the south polar vortex at Saturn's moon Titan still stands out against the orange and blue haze layers that are characteristic of Titan's atmosphere on July 30, 2013.
Darkside of Saturn's Titan
NASA's Cassini spacecraft looks towards the dark side of Saturn's largest moon, Titan, capturing the blue halo caused by a haze layer that hovers high in the moon's atmosphere on November 3, 2013.
Using a special spectral filter, the high-resolution camera aboard NASA's Cassini spacecraft was able to peer through the hazy atmosphere of Saturn's moon Titan on October 7, 2013.
A dynamical interplay between Saturn's largest moon, Titan, and its rings is captured in this view from NASA's Cassini spacecraft on September 20, 2009.
Saturn's moon Enceladus, covered in snow and ice, resembles a perfectly packed snowball in this image from NASA's Cassini mission on March 10, 2012.
The image was taken with the Cassini spacecraft narrow-angle camera using filters sensitive to ultraviolet, visible and infrared light.
NASA's Cassini captures a still and partially sunlit Enceladus on April 7, 2010, using filters sensitive to ultraviolet, visible and infrared light.
Saturn's equinox is captured here in a mosaic of light and dark, September 21, 2009.
The moon Janus (179 kilometers, 111 miles across) is on the lower left of this image. Epimetheus (113 kilometers, 70 miles across) appears near the middle bottom. Pandora (81 kilometers, 50 miles across) orbits outside the rings on the right of the image. The small moon Atlas (30 kilometers, 19 miles across) orbits inside the thin F ring on the right of the image.