R.I.P. Cassini: A photographic tribute

On Friday NASA intentionally crashed its pioneering spacecraft Cassini into Saturn's atmosphere, bringing to a close a 20-year mission of exploration of this unique planet.

The Cassini-Huygens mission, launched on Oct. 15, 1997, was a joint endeavor of NASA, the European Space Agency and the Italian Space Agency and was the first mission to orbit Saturn and explore its environs in detail.

As a result, the findings of the Cassini mission have revolutionized our understanding of Saturn, its complex rings, the amazing assortment of moons and the planet's dynamic magnetic environment.

The following is a photographic tribute of some of the most stunning images taken throughout Cassini's historic scientific mission.

— Images and captions courtesy of NASA/JPL-Caltech/Space Science Institute.

A photo of the Cassini launch was taken by Ken Sturgill of Marion, Virginia, using a 30-second, f 1.8 exposure on 400-speed film on Oct. 15, 1997. The spacecraft was launched from Cape Canaveral Air Force Station's Space Launch Complex 40 using a U.S. Air Force Titan IVB/Centaur rocket.

Cassini-Huygens was one of the most ambitious missions ever launched into space. Loaded with an array of powerful instruments and cameras, the spacecraft is capable of taking accurate measurements and detailed images in a variety of atmospheric conditions and light spectra.

Since Cassini arrived at Saturn in mid-2004, the planet's appearance has changed greatly. The shifting angle of sunlight as the seasons march forward has illuminated the giant hexagon-shaped jet stream around the north polar region, and the subtle bluish hues seen earlier in the mission have continued to fade.

This view shows Saturn's northern hemisphere in 2016, as that part of the planet nears its northern hemisphere summer solstice in May 2017. Saturn's year is nearly 30 Earth years long, and during its long time there, Cassini has observed winter and spring in the north, and summer and fall in the south.

Specially designed Cassini orbits place Earth and Cassini on opposite sides of Saturn's rings, a geometry known as occultation. Scientists have never before studied the size, temperature, composition and distribution of Saturn's rings from Saturn orbit.

Cassini has captured extraordinary ring-moon interactions, observed the lowest ring-temperature ever recorded at Saturn, discovered that the moon Enceladus is the source for Saturn's E ring, and viewed the rings at equinox when sunlight strikes the rings edge-on, revealing never-before-seen ring features and details.

Clouds on Saturn take on the appearance of strokes from a cosmic brush thanks to the wavy way that fluids interact in Saturn's atmosphere.

Neighboring bands of clouds move at different speeds and directions depending on their latitudes. This generates turbulence where bands meet and leads to the wavy structure along the interfaces. Saturn's upper atmosphere generates the faint haze seen along the edge of the planet in this image.

The spinning vortex of Saturn's north polar storm resembles a deep red rose of giant proportions surrounded by green foliage in this false-color image from Cassini.

This view looks toward the anti-Saturn hemisphere of Mimas. The gravitational pull of Mimas (246 miles or 396 km across) creates waves in Saturn's rings that are visible in some Cassini images.

A giant of a moon appears before a giant of a planet undergoing seasonal changes in this natural color view of Titan and Saturn from NASA's Cassini spacecraft.

This zoomed-in view of moon Epimetheus, one of the highest resolutions ever taken, shows a surface covered in craters, vivid reminders of the hazards of space.

Unusual arc-shaped, reddish streaks cut across the surface of Saturn's ice-rich moon Tethys in this enhanced-color mosaic. The red streaks are narrow, curved lines on the moon's surface, only a few miles (or km) wide but several hundred miles (or km) long. The red streaks are among the most unusual color features on Saturn's moons to be revealed by Cassini's cameras.

This is a true-color view of Saturn's north polar region, taken by Cassini's Imaging Science Subsystem on June 26, 2013. Saturn's mysterious hexagon is visible in the center.

This false-color view of Saturn's clouds was made by space imaging enthusiast Kevin M. Gill, who is also an engineer at NASA's Jet Propulsion Laboratory. This image is made from uncalibrated (raw) infrared filtered images from Cassini, taken on July 20, 2016. Kevin mapped the CB2 filtered image (.75 micron wavelength) to red, MT2 (.727 microns) to green, and MT1 (.619 microns) to blue.

This is the highest-resolution color image of any part of Saturn's rings, to date, showing a portion of the inner-central part of the planet's B Ring.

A masterpiece of deep time and wrenching gravity, 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.

Cassini has delivered a glorious view of Saturn, taken while the spacecraft was in Saturn's shadow. The cameras were turned toward Saturn and the sun so that the planet and rings are backlit. In addition to the visual splendor, this special, very-high-phase viewing geometry lets scientists study ring and atmosphere phenomena not easily seen at a lower phase.

In this rare image taken on July 19, 2013, the wide-angle camera on Cassini has captured Saturn's rings and Earth and its moon in the same frame.

This monochrome view is the last image taken by the imaging cameras on NASA's Cassini spacecraft. It looks toward the planet's night side, lit by reflected light from the rings, and shows the location at which the spacecraft would enter the planet's atmosphere hours later.

Cassini Spacecraft Operations Team Manager Julie Webster reacts in mission control at NASA's Jet Propulsion Laboratory after confirmation of Cassini's demise after intentionally plunging into Saturn's atmosphere and ending it's 20-year mission.

The last Cassini project science group meeting on Sept. 12 at Caltech in Pasadena, California, before Cassini plunges into the Saturn atmosphere on Sept. 15.