Saturn's North Polar Hexagon

Nature is often more complex and wonderful than it first appears. For example, although it looks like a simple hexagon, this feature surrounding Saturn's north pole is really a manifestation of a meandering polar jet stream. Scientists are still working to understand more about its origin and behavior.

For more on the hexagon, see PIA11682.

This view looks toward the sunlit side of the rings from about 33 degrees above the ringplane. The image was taken in red light with the Cassini spacecraft wide-angle camera on July 24, 2013.

The view was acquired at a distance of approximately 605,000 miles (973,000 kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 19 degrees. Image scale is 36 miles (58 kilometers) per pixel.

Image credit: NASA/JPL-Caltech/Space Science Institute

Saturn

Saturn's many cloud patterns, swept along by high-speed winds, look as if they were painted on by some eager alien artist.

With no real surface features to slow them down, wind speeds on Saturn can top 1,100 mph (1,800 kph), more than four times the top speeds on Earth.

This view looks toward the sunlit side of the rings from about 29 degrees above the ringplane. The image was taken with the Cassini spacecraft wide-angle camera on April 4, 2014 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 752 nanometers.

The view was obtained at a distance of approximately 1.1 million miles (1.8 million kilometers) from Saturn. Image scale is 68 miles (109 kilometers) per pixel.

Image credit: NASA/JPL-Caltech/Space Science Institute

Saturn's North Polar Hexagon

The giant planet Saturn is mostly a gigantic ball of rotating gas, completely unlike our solid home planet. But Earth and Saturn do have something in common: weather, although the gas giant is home to some of the most bizarre weather in our Solar System, such as the swirling storm shown in this Cassini view.

Known as “the hexagon”, this weather feature is an intense, six-sided jet stream at Saturn’s north pole. Spanning some 30,000 km across, it hosts howling 320 km/h winds that spiral around a massive storm rotating anticlockwise at the heart of the region.

Numerous small vortices rotate in the opposite direction to the central storm and are dragged around with the jet stream, creating a terrifically turbulent region. While a hurricane on Earth may last a week or more, the hexagon has been raging for decades, and shows no signs of letting up.

This false-color image of the hexagon was made using ultraviolet, visible and infrared filters to highlight different regions.

The dark center of the image shows the large central storm and its eye, which is up to 50 times bigger than a terrestrial hurricane eye. The small vortices show up as pink-red clumps. Towards the lower right of the frame is a white-tinted oval storm that is bigger than any of the others — this is the largest of the vortices at some 3500 km across, twice the size of the largest hurricane ever recorded on Earth.

The darker blue region within the hexagon is filled with small haze particles, whereas the paler blue region is dominated by larger particles. This divide is caused by the hexagonal jet stream acting as a shepherding barrier — large particles cannot enter the hexagon from the outside.

These large particles are created when sunlight shines onto Saturn’s atmosphere, something that only started relatively recently in the northern hemisphere with the beginning of northern spring in August 2009.

Cassini will continue to track changes in the hexagon, monitoring its contents, shape and behavior as summer reaches Saturn’s northern hemisphere in 2017.

An animated version is available here.

Image credit: NASA/JPL-Caltech/SSI/Hampton University

Saturn's North Polar Vortex and Rings

The Cassini spacecraft captures three magnificent sights at once: Saturn's north polar vortex and hexagon along with its expansive rings.

The hexagon, which is wider than two Earths, owes its appearance to the jet stream that forms its perimeter. The jet stream forms a six-lobed, stationary wave which wraps around the north polar regions at a latitude of roughly 77 degrees North.

This view looks toward the sunlit side of the rings from about 37 degrees above the ringplane. The image was taken with the Cassini spacecraft wide-angle camera on April 2, 2014 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 752 nanometers.

The view was obtained at a distance of approximately 1.4 million miles (2.2 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 43 degrees. Image scale is 81 miles (131 kilometers) per pixel.

Image credit: NASA/JPL-Caltech/Space Science Institute

Saturn's Northern Hemisphere Storm, 6 March 2011

Like a swirl from a paintbrush being dipped in water, this image from the Cassini orbiter shows the progress of a massive storm on Saturn. The storm first developed in December 2010, and this mosaic captures how it appeared on 6 March 2011.

The head of the storm is towards the left of the image, where the most turbulent activity is shown in white, but towards the center you can also see the trace of a spinning vortex in the wake of the storm.

This image, centered at about 0º longitude and 35º N latitude, has had its colors enhanced to help reveal the complex processes in Saturn’s weather. The white corresponds to the highest cloud tops, but to the human eye the storm would appear more as a bright area against a yellow background.

Cassini also monitored the temperature of the storm, showing a rapid spike as energy was released into the atmosphere.

The storm grew so large that on Earth it would easily cover all of Europe. Atmospheric disturbances of this size can be expected once during each of Saturn’s orbits around the Sun, which takes 30 Earth years. However, this particular event surprised scientists by occurring during the northern hemisphere spring, rather than the more typically stormy Saturnian summer.

Image credit: NASA/JPL-Caltech/SSI/Hampton University

Saturn's North Polar Hexagon

Earth's jet stream is a subject of intense interest and concern thanks to its effects on our weather. Saturn's polar jet stream, seen here, causes no such worries for Earthlings, so we can simply marvel at its graceful form.

This atmospheric feature was first observed by Voyager and was dubbed 'the hexagon'. To see more of this feature, see PIA10486 and PIA11682.

This view looks toward the north pole of Saturn from about 53 degrees above the ringplane. The image was taken with the Cassini spacecraft wide-angle camera on July 23, 2013 using a spectral filter sensitive to wavelengths of near-infrared light centered at 752 nanometers.

The view was obtained at a distance of approximately 590,000 miles (949,000 kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 52 degrees. Image scale is 35 miles (57 kilometers) per pixel.

Photo credit: NASA/JPL-Caltech/Space Science Institute

Saturn's North Polar Hexagon

This colorful view from NASA's Cassini mission is the highest-resolution view of the unique six-sided jet stream at Saturn's north pole known as "the hexagon." This movie, made from images obtained by Cassini's imaging cameras, is the first to show the hexagon in color filters, and the first movie to show a complete view from the north pole down to about 70 degrees north latitude.

Scientists can see the motion of a wide variety of cloud structures that reside within the hexagon in this movie. There is a massive hurricane tightly centered on the north pole, with an eye about 50 times larger than the average hurricane eye on Earth. (More information about that Saturn hurricane is at PIA14947.) Numerous small vortices are also present, which appear as reddish ovals. Some of these vortices spin clockwise while the hexagon and hurricane spin counterclockwise. Some of those smaller features are swept along with the jet stream of the hexagon, as if on a racetrack. The biggest of these vortices, seen near the lower right corner of the hexagon and appearing whitish, spans about 2,200 miles (3,500 kilometers), approximately twice the size of the largest hurricane on Earth.

The differences in this version of the movie, in which different wavelengths of light from ultraviolet to visible to infrared have been assigned colors, show a distinct contrast between the types of atmospheric particles inside and outside the hexagon. Inside the hexagon there are fewer large haze particles and a concentration of small haze particles, while outside the hexagon, the opposite is true. The jet stream that makes up the hexagon seems to act like a barrier, which results in something like the "ozone hole" in the Antarctic.

This movie shows a view from directly over the north pole, keeping up with the rotation of the planet so that all the motion seen on the screen is the motion of the hexagonal jet stream or the storms inside of it, without any added motion from the spinning of the planet itself. The original images were re-projected to show this polar view.

High-resolution views of the hexagon have only recently become possible because of the changing of the seasons at Saturn and changes in the Cassini spacecraft's orbit. The north pole was dark when Cassini first arrived in July 2004. The sun really only began to illuminate the entire interior of the hexagon in August 2009, with the start of northern spring. In late 2012, Cassini began making swings over Saturn's poles, giving it better views of the hexagon.

The eight frames of the movie were captured over 10 hours on December 10, 2012. Each of the eight frames consists of 16 map-projected images (four per color filter, and four filters per frame) so the movie combines data from 128 images total.

In this color scheme, scientists assigned red to the 0.750-micron part of the light spectrum (near infrared). This part of the spectrum penetrates the high-altitude haze layer to sense the top of tropospheric cloud deck. They assigned green to the 0.727-micron part of the light spectrum that senses the upper tropospheric haze (a near-infrared wavelength corresponding to a methane absorption band). They assigned blue to the sum of blue and ultraviolet broadband filters -- combined, this blue channel covers between 0.400 and 0.500 microns (covering very near ultraviolet to blue in visible light). This part of the spectrum is sensitive to small aerosols.

To human eyes, the hexagon and north pole would appear in tones of gold and blue. See PIA14945 for a still image of the area in natural color.

Video credit: NASA/JPL-Caltech/SSI/Hampton University

Note: For more information, see PIA17653: Hexagon in Silhouette, PIA17654: Looking Down on the Hexagon in Infrared, and NASA's Cassini Spacecraft Obtains Best Views of Saturn Hexagon.

Saturn

A swing high above Saturn by NASA's Cassini spacecraft revealed this stately view of the golden-hued planet and its main rings. The view is in natural color, as human eyes would have seen it. This mosaic was made from 36 images in three color filters obtained by Cassini's imaging science subsystem on October 10, 2013. The observation and resulting image mosaic were planned as one of three images for Cassini's 2013 Scientist for a Day essay contest.

Saturn sports differently colored bands of weather in this image. For instance, a bright, narrow wave of clouds around 42 degrees north latitude appears to be some of the turbulent aftermath of a giant storm that reached its violent peak in early 2011. The mysterious six-sided weather pattern known as the hexagon is visible around Saturn's north pole.

When Cassini arrived in 2004, more of the northern hemisphere sported a bluish hue and it was northern winter. The golden tones dominated the southern hemisphere, where it was southern summer. But as the seasons have turned and northern spring is in full swing, the colors have begun to change in each hemisphere as well. Golden tones have started to dominate in the northern hemisphere and the bluish color in the north is now confined to a tighter circle around the north pole. The southern hemisphere has started getting bluer, too.

The rings shown here include Saturn's main rings. The innermost D ring, and the C, B and A rings are easily seen. The F ring is also there, but not easily seen without enhancing the contrast of the image. (Rings were named in order of their discovery rather than their position around Saturn.) The rings also cast a shadow on Saturn at the limb of the planet in the lower right quadrant.

Cassini is currently in a set of tilted orbits known as "inclined orbits" that allow it to swing up over the north pole and below the south pole. Much of Cassini's time is spent close to the equatorial plane, where most of Saturn's rings and moons are located.

Image credit: NASA/JPL-Caltech/SSI/Cornell

Note: For more information, see Cassini Swings Above Saturn to Compose a Portrait.

Saturn's Northern Hemisphere Storm in Visual and Infrared

This set of images from NASA's Cassini mission shows the turbulent power of a monster Saturn storm. The visible-light image in the back, obtained on February 25, 2011, by Cassini's imaging camera, shows the turbulent clouds churning across the face of Saturn. The inset infrared image, obtained a day earlier, by Cassini's visual and infrared mapping spectrometer, shows the dredging up of water and ammonia ices from deep in Saturn's atmosphere. This was the first time water ice was detected in Saturn's atmosphere. The storm, first detected by Cassini's radio and plasma wave subsystem in December 2011, churned around the planet in a band around 33 degrees north.

The visible-light image can be seen separately at PIA12826.

Image credit: NASA/JPL-Caltech/SSI/University of Arizona/University of Wisconsin

Note: For more information, see Cassini Sees Saturn Storm's Explosive Power.

Saturn's North Polar Hexagon

The weather forecast for Saturn's north pole: storms. Lots and lots of storms. Here, the area within Saturn's north polar hexagon is shown to contain myriad storms of various sizes, not the least of which is the remarkable and imposing vortex situated over the planet's north pole.

The north polar hexagon was first observed by Voyager. To see more of the hexagon, see PIA10486 and PIA11682.

This view is centered on Saturn's north pole. North is up and rotated 33 degrees to the left. The image was taken with the Cassini spacecraft wide-angle camera on June 14, 2013 using a spectral filter sensitive to wavelengths of near-infrared light centered at 752 nanometers.

The view was obtained at a distance of approximately 476,000 miles (766,000 kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 45 degrees. Image scale is 26 miles (42 kilometers) per pixel.

Photo credit: NASA/JPL-Caltech/Space Science Institute

Video of Saturn's North Polar Hurricane

This movie, made from images obtained by NASA's Cassini spacecraft, shows the clouds of a hurricane-like storm, which circulate around the north pole of Saturn out to 88.5 degrees north latitude. The latitude of the bright ring of clouds is 89.0 degrees, which is about 587 miles (945 kilometers) from the pole. The eye of the storm is about 20 times larger than the average hurricane eye on Earth.

Winds are measured by following small clouds over a five-hour period. The winds at the inner ring are moving the fastest, at speeds of about 330 mph (50 meters per second) relative to the nominal rate for the planet established by NASA's Voyager spacecraft in 1980. These winds are four times the speed of the Earth's jet streams and more than four times the definition of a hurricane force wind on Earth. (Hurricane force winds blow at 74 mph, or 119 kilometers per hour.)

The clouds at the very center are spinning rapidly -- almost twice as fast as the planet itself, with a period just over six hours. The direction of rotation is counterclockwise, like a northern hemisphere hurricane on Earth, except there is no ocean underneath. A similar feature exists at Saturn's southern pole, and it spins in the same direction as that of a southern hemisphere hurricane on Earth. However, the hurricanes on Earth begin in the tropics and drift around. The polar hurricanes on Saturn are locked to their poles.

The bright clouds form a tightly wrapped spiral that traces a path toward the center as one follows it in a counterclockwise direction. This spiral could be a wave or actual particle motion toward the center from a disturbance further out. Or it could be the remnants of a compact cloud that got sheared apart by the higher angular velocity closer to the center. Choosing among these possibilities is the subject of ongoing research. Other ongoing research involves inferring cloud heights, both from the changing shadows as the sun moves relative to the features, and from the appearance of the clouds in other wavelengths, not shown in this set of black and white images.

This set of images is among the first sunlit views of Saturn's north pole captured by Cassini's imaging cameras. When the spacecraft arrived in the Saturnian system in 2004, it was northern winter and the north pole was in darkness.

The movie was constructed from seven images taken over five hours by Cassini's imaging science subsystem when the spacecraft was about 45 degrees above the horizon. Imaging team scientists re-projected the images to show a view from directly over the pole, keeping up with the rotation of the planet to make the clouds at 89.3 degrees latitude appear stationary. The winds at other latitudes produce the motion seen on the screen. They determined the rotation rate at each latitude, and interpolated in time to make a 200-step movie that flows smoothly as the clouds swirl around the center. To show the features at the center, the movie displays the motion relative to the clouds at 89.3 degrees latitude.

Video credit: NASA/JPL-Caltech/SSI


Note: For more information, see Mysterious Hurricane at Saturn's North Pole, NASA Probe Gets Close-Up Views of Large Hurricane on Saturn, Saturn's North-Pole Hurricane Close Up, and Gigantic Hurricane Spotted on Saturn.

Saturn's North Polar Hurricane in (Psychadelic) False Colors

This spectacular, vertigo inducing, false-color image from NASA's Cassini mission highlights the storms at Saturn's north pole. The angry eye of a hurricane-like storm appears dark red while the fast-moving hexagonal jet stream framing it is a yellowish green. Low-lying clouds circling inside the hexagonal feature appear as muted orange color. A second, smaller vortex pops out in teal at the lower right of the image. The rings of Saturn appear in vivid blue at the top right.

The images were taken with Cassini's wide-angle camera using a combination of spectral filters sensitive to wavelengths of near-infrared light. The images filtered at 890 nanometers are projected as blue. The images filtered at 728 nanometers are projected as green, and images filtered at 752 nanometers are projected as red. At Saturn, this scheme means colors correlate to different altitudes in the planet's polar atmosphere: red indicates deep, while green shows clouds that are higher in altitude. High clouds are typically associated with locations of intense upwelling in a storm. These images help scientists learn the distribution and frequencies of such storms. The rings are bright blue in this color scheme because there is no methane gas between the ring particles and the camera.

The view was acquired at a distance of approximately 261,000 miles (419,000 kilometers) from Saturn and at a sun-Saturn-spacecraft, or phase, angle of 94 degrees. Image scale is 13 miles (22 kilometers) per pixel.

Image credit: NASA/JPL-Caltech/SSI


Note: For more information, see Mysterious Hurricane at Saturn's North Pole, NASA Probe Gets Close-Up Views of Large Hurricane on Saturn, Saturn's North-Pole Hurricane Close Up, and Gigantic Hurricane Spotted on Saturn.

Saturn's North Polar Hurricane in Natural Color

The north pole of Saturn, in the fresh light of spring, is revealed in this color image from NASA's Cassini spacecraft. The north pole was previously hidden from the gaze of Cassini's imaging cameras because it was winter in the northern hemisphere when the spacecraft arrived at the Saturn system in 2004.

A hurricane-like storm circling Saturn's north pole at about 89 degrees north latitude is inside the famous "hexagon" feature, which scientists think is a wandering jet stream that whips around the north pole at about 220 miles per hour (98 meters per second). It folds into a six-sided shape because the hexagon is a stationary wave that guides the path of the gas in the jet. The hexagon borders occur at about 77 degrees north latitude and the feature is wider than two Earths. Saturn's rings can be seen at the upper right of the image.

Images with red, green and blue spectral filters were combined to create this natural-color view, which is what the human eye would see if we were there at Saturn. The image here was acquired with the Cassini spacecraft wide-angle camera on Nov. 27, 2012 at a distance of approximately 260,000 miles (418,000 kilometers) from Saturn and at a sun-Saturn-spacecraft, or phase, angle of 96 degrees. Image scale is 18 miles (28.6 kilometers) per pixel.

A false-color version of this image can be seen at PIA14946.

Image credit: NASA/JPL-Caltech/SSI


Note: For more information, see Mysterious Hurricane at Saturn's North Pole, NASA Probe Gets Close-Up Views of Large Hurricane on Saturn, Saturn's North-Pole Hurricane Close Up, and Gigantic Hurricane Spotted on Saturn.

False Color Image of Saturn's North Pole Hurricane

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 NASA's Cassini spacecraft. Measurements have sized the eye at a staggering 1,250 miles (2,000 kilometers) across with cloud speeds as fast as 330 miles per hour (150 meters per second).

This image is among the first sunlit views of Saturn's north pole captured by Cassini's imaging cameras. When the spacecraft arrived in the Saturnian system in 2004, it was northern winter and the north pole was in darkness. Saturn's north pole was last imaged under sunlight by NASA's Voyager 2 in 1981; however, the observation geometry did not allow for detailed views of the poles. Consequently, it is not known how long this newly discovered north-polar hurricane has been active.

The images were taken with the Cassini spacecraft narrow-angle camera on November 27, 2012, using a combination of spectral filters sensitive to wavelengths of near-infrared light. The images filtered at 890 nanometers are projected as blue. The images filtered at 728 nanometers are projected as green, and images filtered at 752 nanometers are projected as red. In this scheme, red indicates low clouds and green indicates high ones.

The view was acquired at a distance of approximately 261,000 miles (419,000 kilometers) from Saturn and at a sun-Saturn-spacecraft, or phase, angle of 94 degrees. Image scale is 1 mile (2 kilometers) per pixel.

Image credit: NASA/JPL-Caltech/SSI

Note: For more information, see Mysterious Hurricane at Saturn's North Pole, NASA Probe Gets Close-Up Views of Large Hurricane on Saturn, Saturn's North-Pole Hurricane Close Up, and Gigantic Hurricane Spotted on Saturn.

Saturn's Clouds and Storms

Saturn's richly dynamic atmosphere rewards viewers with unique and fascinating structures with every new observation. Here, the Cassini spacecraft uses the near-infrared filters on its wide-angle camera to get a better look at some of Saturn's cloud patterns, shaped by wind and storms in Saturn's atmosphere.

This view is centered on 30 degrees north latitude, 42 degrees west longitude. North is up and rotated 44 degrees to the right. The image was taken with the Cassini spacecraft wide-angle camera on December 24, 2012 using a spectral filter sensitive to wavelengths of near-infrared light centered at 752 nanometers.

The view was acquired at a distance of approximately 440,000 miles (710,000 kilometers) from Saturn's surface and at a Sun-Saturn-spacecraft, or phase, angle of 14 degrees. Image scale is 26 miles (42 kilometers) per pixel.

Photo credit: NASA/JPL-Caltech/Space Science Institute

Rain from Saturn's Rings

This artist's concept illustrates how charged water particles flow into the Saturnian atmosphere from the planet's rings, causing a reduction in atmospheric brightness. The observations were made with the W.M. Keck Observatory on Mauna Kea, Hawaii, with NASA funding. The analysis was led by the University of Leicester, England.

Image credit: NASA/JPL-Caltech/Space Science Institute/University of Leicester

Note: For more information, see Blame it on the Rain (from Saturn's Rings).

North Polar Hexagon and Rings

Saturn's north polar hexagon basks in the Sun's light now that spring has come to the northern hemisphere. Many smaller storms dot the north polar region and Saturn's signature rings, which appear to disappear on account of Saturn's shadow, put in an appearance in the background.

The north polar hexagon was first observed by Voyager. To see more of the hexagon, see PIA10486 and PIA11682.

The image was taken with the Cassini spacecraft's wide-angle camera on November 27, 2012 using a spectral filter sensitive to wavelengths of near-infrared light centered at 750 nanometers.

The view was acquired at a distance of approximately 403,000 miles (649,000 kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 21 degrees. Image scale is 22 miles (35 kilometers) per pixel.

Photo credit: NASA/JPL-Caltech/Space Science Institute

Northern Storm in Full Force

This mosaic of images from NASA's Cassini spacecraft shows the trail of a great northern storm on Saturn raging in full force. The contrast in the images has been enhanced to make the turbulent parts of the storm (in white) stand out without losing the details of the surrounding regions.

The head of the storm is the set of bright clouds near the left of the image. A clockwise-spinning vortex spawned by the storm shortly after it erupted in early December 2010 can be seen in the middle. The head of the storm moved very swiftly westward, while the vortex drifted more slowly westward.

Cassini's imaging camera obtained the images that went into this mosaic on March 6, 2011. The image is centered at about 0 degrees longitude and 35 degrees latitude.

In this image, scientists assigned red, green and blue channels to those visible-light colors. However, this view is not what a human eye would see at Saturn -- in enhancing the contrast, the natural color balance was not preserved. To human eyes, storm would have appeared more like a bright feature against a yellow background with less color variation, as is seen in PIA16724. In this color scheme, the brightness generally corresponds to the altitude of the cloud features. Bright white indicates highest cloud tops in the troposphere, and dark places indicate holes in the cloud layer. The subtle colors that become apparent in this enhanced-contrast view are probably produced by variation in the composition of clouds. However, the coloring agents responsible for producing these subtle hues remain unidentified.

Image credit: NASA/JPL-Caltech/SSI/Hampton University

First Chapter of the Northern Storm

This mosaic of false-color images from NASA's Cassini spacecraft shows what a giant storm in Saturn's northern hemisphere looked like about a month after it began. The bright head of the storm is on the left. The storm also spawned a clockwise-spinning vortex, seen as the light blue circular feature framed with a curl of bright clouds a little to the right of the storm head.

Cassini's imaging camera obtained the images that went into this mosaic on January 11, 2011. The storm erupted in early December 2010 and the head of the storm began moving rapidly westward. The vortex, spun off from the head of the storm in early December shortly after the storm began, drifted much more slowly. In August 2011, the head ran into the vortex, like a version of the mythical serpent that bites its own tail. By late August, the convective phase of the storm was over.

The colors indicate the altitudes of the clouds -- red is the lowest, green is an intermediate level and blue is the highest. White indicates thick clouds at a high altitude. Scientists assigned red to a wavelength of radiation that penetrates the atmosphere deep down to the top of the tropospheric cloud deck (750 nanometers). The troposphere is the part of the atmosphere where weather occurs. They assigned green to the 728-nanometer wavelength. Blue is a wavelength band that penetrates only to the top of tropospheric haze (890 nanometer).

Image credit: NASA/JPL-Caltech/SSI/Hampton University

Six Views of the Northern Hemisphere Vortex

A vortex that was part of a giant storm on Saturn slowly dissipates over time in this set of false color images from NASA's Cassini spacecraft. This clockwise vortex spun off the bright head of the storm shortly after the thunder-and-lightning storm erupted in early December 2010.

The top left image shows the vortex's most turbulent activity captured by Cassini's imaging cameras on January 11, 2011. It was centered around 54 degrees west longitude and 35 degrees north latitude. At the time, it was the largest vortex ever observed in Saturn's troposphere, which is the layer of the atmosphere where weather occurs. It measured up to 7,500 miles (12,000 kilometers) across. This is comparable in size to the giant storm on Jupiter known as Oval BA, though Oval BA and Jupiter's more famous storm -- the Great Red Spot -- are not thunder-and-lightning storms. Jupiter's vortices are known for their stability and longevity. Precursors to Oval BA formed in the 1930s, and evolved into what finally became Oval BA in the late 1990s. The Great Red Spot has been in existence at least since 1879, and possibly since 1664. Jupiter and Saturn are similar in many respects. However, why Jupiter's vortices are long-lived and why Saturnian ones are so short remain a mystery.

The image in the top middle was taken on March 17, 2011, when the center of the vortex had drifted west to around 6 degrees west longitude. The image on the top right was taken on April 25, 2011, when the vortex had moved to about 315 degrees west longitude.

The bright head of the storm was moving more quickly westward than the vortex and collided with the vortex by mid-June. The image at bottom left was obtained on July 12, 2011, after the head and vortex collided. The vortex here is less turbulent and is centered around 247 degrees west longitude. The bottom middle image was taken on August 24, 2011, about four days before the storm's thunder and lightning ceased completely. The vortex is swirling at about 218 degrees west longitude. The bottom right image was taken on October 6, 2011, when the vortex had nearly faded away. What is left of the vortex is centered around 248 degrees west longitude.The colors in these images denote the altitudes of the clouds – with red being the lowest, green being an intermediate level and blue being the highest. White indicates thick clouds at a high altitude. Scientists assigned the red color channel to a wavelength of radiation that penetrates the atmosphere deep down to the top of the tropospheric cloud deck (750 nanometers). They assigned blue to a wavelength that penetrates only to the top of tropospheric haze (890 nanometers). Green represents an intermediate wavelength above the troposphere (728 nanometers).

Image credit: NASA/JPL-Caltech/SSI/Hampton University

Note: For other images in this series, see PIA16722: Which Way the Wind Blows, PIA16723: Swirling Vortex, and PIA16724: Great Disturbances. Also, NASA's Cassini Watches Storm Choke on Its Own Tail.