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Saturn: the "Ringed Beauty" and His Moons
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Saturn-PIA08303.jpgMore "Streamers" on sight!75 visiteA shepherd moon can do more to define ring structures than just keep the flock of particles in line, as Cassini spacecraft images such as this have shown.
Prometheus is seen here with two long streamers of material that it has pulled out of the F-Ring. When Prometheus comes close to the F-Ring in its orbit, the moon's gravity tugs on the ring particles. The disturbed particles, now pulled into orbits slightly closer to Saturn and therefore faster, shear out during successive orbits, creating the long and delicate streamers seen here.
This view looks toward the unlit side of the Rings from about 31 above the Ring-Plane.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Sept. 29, 2006 at a distance of approx. 1,7 MKM (a little more than 1 MMs) from Prometheus and at a Sun-Prometheus-spacecraft, or phase, angle of 160.
Image scale is roughly 10 Km (about 6 miles) per pixel.
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Saturn-PIA08332.jpgA "Hole" in the (South) "Pole"69 visiteCassini stares deep into the swirling hurricane-like vortex at Saturn's south pole, where the vertical structure of the clouds is highlighted by shadows. Such a storm, with a well-developed eye ringed by towering clouds, is a phenomenon never before seen on another planet.
This 14-frame movie shows a swirling cloud mass centered on the south pole, around which winds blow at 550 kilometers (350 miles) per hour. The frames have been aligned to make the planet appear stationary, while the sun appears to revolve about the pole in a counterclockwise direction. The clouds inside the dark, inner circle are lower than the surrounding clouds, which cast a shadow that follows the sun.
At the beginning of the movie, the sun illuminates directly from the top, and by the end it illuminates from the left. The width of the shadow and the height of the sun above the local horizon yield a crude estimate of the height of the surrounding clouds relative to the clouds in the center. The shadow-casting clouds tower 30 to 75 kilometers (20 to 45 miles) above those in the center. This is two to five times greater than the tallest terrestrial thunderstorms and two to five times the height of clouds surrounding the eye of a terrestrial hurricane. Such a height difference arises because Saturn's hydrogen-helium atmosphere is less dense at comparable pressures than Earth's atmosphere, and is therefore more distended in the vertical dimension.
The south polar storm, which displays two spiral arms of clouds extending from the central ring and spans the dark area inside a thick, brighter ring of clouds, is approximately 8,000 kilometers (5,000 miles) across, which is considerably larger than a terrestrial hurricane.
Eye-wall clouds are a distinguishing feature of hurricanes on Earth. They form where moist air flows inward across the ocean's surface, rising vertically and releasing a load of precipitation around an interior circular region of descending air, which is the eye itself.
Though it is uncertain whether moist convection is driving this storm, as is the case with Earthly hurricanes, the dark 'eye' at the pole, the eye-wall clouds and the spiral arms together indicate a hurricane-like system. The distinctive eye-wall clouds especially have not been seen on any planet beyond Earth. Even Jupiter's Great Red Spot, much larger than Saturn's polar storm, has no eye, no eye-wall, and is relatively calm at the center.
This giant Saturnian storm is apparently different from hurricanes on Earth because it is locked to the pole, does not drift around like terrestrial hurricanes and because it does not form over liquid water oceans.
The images were acquired over a period of three hours on Oct. 11, 2006, when Cassini was approximately 340,000 kilometers (210,000 miles) from Saturn. Image scale is about 17 kilometers (11 miles) per pixel. The images were taken with the wide-angle camera using a spectral filter sensitive to wavelengths of infrared light centered at 752 nanometers. All frames have been contrast enhanced using digital image processing techniques. The unprocessed images show an oblique view toward the pole, and have been reprojected to show the planet from a perspective directly over the south pole.
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Saturn-PIA08333.jpgThe VERY RESTLESS South Pole of Saturn65 visiteThese images of Saturn's south pole, taken by two different instruments on Cassini, show the hurricane-like storm swirling there and features in the clouds at various depths surrounding the pole. Different wavelengths reveal the height of the clouds, which span tens of kilometers in altitude.
The four monochrome images displayed here were acquired by the imaging science subsystem; the blue and red images in the bottom row were taken by the visual and infrared mapping spectrometer. The images are arranged in order of increasing wavelength in nanometers as follows: (top row) 460 nm, 752 nm, 728 nm; (bottom row) 890 nm, 2,800 nm, 5,000 nm.
At the center of the cauldron of storms spinning around the south pole is the south pole itself, which literally appears to be the eye of this vast polar storm system. As in a hurricane on Earth, the south polar "eye" is relatively clear of clouds and is surrounded by a wall of towering clouds that cast shadows into the center. However, while morphologically similar, it is not clear if this vortex operates in the same fashion as a terrestrial hurricane. In most of the images, the center of the polar storm is quite dark, indicating an unusually cloud-free atmosphere in the upper skies, which are otherwise typically inhabited by bright ammonia clouds. This polar hole in the ammonia cloud layer represents the eye of the hurricane-like storm. Unusually dark clouds likely exist at the bottom of this deep hole, enhancing the murkiness there.
The first image in this montage (at upper left) shows a muted eye, due to the enhanced scattering of light from the atmosphere itself at this blue wavelength (460 nanometers), just as in the blue skies of Earth. In the last image at bottom right, the eye appears relatively bright. This image is taken at a wavelength of 5,000 nanometers, where the dominant source of light is the thermal glow of the planet itself. The bright thermal glow seen in this polar hole again shows that the eye is relatively cloud-free to unusual depths.
In the imaging science subsystem images, the eye looks dark at wavelengths where methane gas absorbs the light (728 nanometers and 890 nanometers, at upper right and lower left) and only the highest clouds are visible, confirming that the clouds within the eye are deeper than their surroundings. This effect is also seen in visual and infrared mapping spectrometer images that show gas absorption.
In the visual and infrared mapping spectrometer image taken at 2,800 nanometers, four times the wavelength of light visible to the human eye, this cloud clearing appears dark, which is consistent with the idea that the atmosphere above any distinct clouds is unusually deep there. The eye is some 1,500 kilometers (930 miles) across, and is surrounded by a distinct ring of clouds some 300 kilometers (185 miles) across. The images also indicate the prevalence of smaller but vertically well-developed storms across the entire south polar region, indicating the extent to which convection characterizes the area.
Literally hundreds of storm clouds encircle the pole, appearing as dark spots in the infrared spectrometer thermal image (red image) and as both bright and dark spots in images taken in sunlight (blue image). Each of these spots represents a storm. These pictures reveal that Saturn's south pole is a cauldron of storm activity, unlike anything ever seen on any planet.
The individual storms surrounding the pole are seen as dark "leopard spots" in the thermal image (red) taken at a wavelength of 5,000 nanometers, some seven times the wavelength of light visible to the human eye. Here, these spots are blocking the thermal light, or heat, from the interior of Saturn. The storm clouds are thus seen in silhouette against Saturn's thermal glow. The effectiveness of these clouds in blocking Saturn's interior thermal glow indicates that the storm clouds are unusually thick, extending deep down into Saturn's atmosphere, and are comprised of relatively large cloud particles, likely condensates formed in upwelling air currents.
The large number of dark, circular leopard spots at the south pole seen at 5,000 nanometer wavelength, and their correlation with the features seen in sunlight at 2,800 nanometer wavelength, indicates that convective activity extending over dozens of kilometers in altitude is surprisingly rampant in the south polar region. Why such unusual dynamics exist there is perhaps linked to Saturn's southern summer, which is the season Saturn is in now. Observations taken over the next few years, as the south pole season changes from summer to fall, will help scientists understand the role seasons play in driving the dramatic meteorology at the south pole of Saturn. The images in this montage were acquired on Oct. 11, 2006, when Cassini was approximately 340,000 kilometers (210,000 miles) from Saturn. The original imaging science subsystem images have a scale of about 17 kilometers (11 miles) per pixel. The visual and infrared spectrometer images have a scale of about 174 kilometers (108 miles) per pixel. The images have been resized to approximately the same scale for presentation here.
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Saturn-PIA08334.jpgThe temperature of Saturn's "Stormy" South Pole73 visiteThe Cassini data presented in this view appear to confirm a region of warm atmospheric descent into the eye of a hurricane-like storm locked to Saturn's south pole. The view shows temperature data from the Cassini spacecraft composite infrared spectrometer overlaid onto an image from the imaging science subsystem wide-angle camera.
The composite infrared spectrometer data refer to a depth in Saturn's upper stratosphere where the pressure is 0.5 millibars (324 kilometers above the 1-bar level), a region higher than that imaged by the imaging camera and visual and infrared spectrometer during the same observation period. The composite infrared spectrometer data show a very small hot spot over the pole, similar in size to the "eye" of the storm seen in the imaging science subsystem images. See also Looking Saturn in the Eye and Saturn's Surprisingly Stormy South for related images.
The color scale at the bottom indicates the temperature in Kelvin corresponding to the colors of the temperature map. Numbers on the grid correspond to lines of latitude and longitude on the planet.
Infrared images taken through the Keck I telescope by ground-based observers had previously shown the south polar spot to be warm. Cassini's composite infrared spectrometer has confirmed this with higher resolution temperature maps of the area (like the map displayed here) and sees a temperature increase of about 2 Kelvin (4 degrees Fahrenheit) at the pole.
The temperatures are in the stratosphere and higher up than the clouds seen by the Cassini imaging and visual and infrared mapping spectrometer instruments, but they suggest that the atmosphere sinks over the south pole. Because the pressure increases with depth, the descending atmosphere compresses and heats up. The warmer temperatures over the south pole also indicate that the vortex winds are decaying with height in the stratosphere. The descent implied by the temperatures nicely supports the lower cloud altitudes observed by the imaging camera and visual and infrared spectrometer instruments at the pole.
The image and atmospheric data were acquired on Oct. 11, 2006, when Cassini was approximately 340,000 kilometers (210,000 miles) from Saturn. The wide-angle camera image was taken using a spectral filter sensitive to wavelengths of infrared light centered at 752 nanometers. The image has been contrast enhanced using digital image processing techniques. The unprocessed image shows an oblique view toward the pole, and was reprojected to show the planet from a perspective directly over the south pole. Scale in the original image was about 17 kilometers (11 miles) per pixel.
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Saturn-PIA08340.jpgShadowlands65 visiteL'espressione "Shadowland/s" l'avevamo inventata un paio d'anni fa, per commentare le immagini che mostravano il profilo di rilievi elevati i quali si trovavano, al momento di effettuazione della ripresa, sul cosiddetto "Terminatore" (ossa la linea che divide il giorno dalla notte).
E' non solo curioso ma anche, ed almeno dal nostro punto di vista, fonte di piacere il fatto di vedere che la NASA - chiss, forse anche ispirata da qualcuno dei "titoli" che diamo alle immagini... - abbia adottato questa medesima espressione per descrivere il regno di ombre che sembra caratterizzare, nel frame in oggetto, il Gigante Anellato pi famoso del Sistema Solare: Saturno.
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Saturn-PIA08357.jpgCrescent Saturn65 visiteCaption NASA:"Cassini coasts beneath giant Saturn, staring upward at its gleaming crescent and icy rings.
A great bull's-eye pattern is centered on the South Pole, where a vast, hurricane-like storm spins.
This view looks toward the lit side of the Rings from about 26 below the Ring-Plane. The view was acquired about 2 hours prior to "The Lore of Saturn".
Images taken using red, green and blue spectral filters were combined to create this natural-color view.
The images were obtained with the Cassini spacecraft wide-angle camera on Jan. 30, 2007, from a distance of approx. 1,1 MKM (about 700.000 miles) from Saturn.
Image scale is roughly 61 Km (about 38 miles) per pixel".MareKromium
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Saturn-PIA08358.jpgThe Northern Regions of Saturn78 visiteCaption NASA:"Magnificent blue and gold Saturn floats obliquely as one of its gravity-bound companions, Dione, hangs in the distance. The darkened Rings seem to nearly touch their shadowy reverse images on the planet below.
This view looks toward the unlit side of the Rings from about 9 above the Ring-Plane. The Rings glow feebly in the scattered light that filters through them.
The image was taken in visible light with the Cassini spacecraft wide-angle camera on Feb. 4, 2007, at a distance of approx. 1,2 MKM (about 800.000 miles) from Saturn.
Image scale is roughly 75 Km (about 47 miles) per pixel".MareKromium
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Saturn-PIA08359.jpgThe Southern Regions of Saturn66 visiteCaption NASA:"With pastel blues, pinks, greens and golds, Saturn displays a dazzling diversity of colors and hues.
Here, Cassini looks upward at, and through, the sunlit side of the Rings from about 19 below the Ring-Plane. The small moon Janus can be spotted off the Planet's Western Limb (edge) near the image bottom.
Images taken using red, green and blue spectral filters were combined to create this natural-color view. The images were obtained with the Cassini spacecraft wide-angle camera on Feb. 3, 2007, at a distance of approx. 1,1 MKM (about 700.000 miles) from Saturn.
Image scale is roughly 60 Km (about 38 miles) per pixel".MareKromium
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Saturn-PIA08360.jpgFrom North to South...65 visiteCaption NASA:"Dark and sharply defined ring shadows appear to constrict the flow of color from Saturn's warmly hued South to the bluish Northern Latitudes.
Scientists studying Saturn are not yet sure about the precise cause of the color change from North to South. NASA Voyager spacecraft flybys witnessed a more evenly painted Planet in the early '80s, when Saturn was closer to Equinox. However, the bluish color was readily apparent upon Cassini's approach to the Planet in late 2003, when Saturn was just coming out of its Northern Hemisphere Winter. Scientists have speculated that the color is due to seasonal effects on the atmosphere.
Aside from the color differences, the cloud morphology is quite different in the Polar Regions compared to the mid-latitudes. Bright, isolated clouds dot the high latitudes, while Saturn's middle is characterized by flowing cloud bands and the occasional bright or dark vortex.
This view looks toward the lit side of the rings from about half a degree below the Ring-Plane.
Images taken using red, green and blue spectral filters were combined to create this natural-color view. The images were obtained with the Cassini spacecraft wide-angle camera on Feb. 4, 2007, at a distance of approx. 1,2 MKM (about 700.000 miles) from Saturn. Image scale is roughly 67 Km (about 42 miles) per pixel". MareKromium
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Saturn-PIA08361.jpgThe Ring-World in natural colors64 visiteCaption NASA:"Our robotic emissary, flying high above Saturn, captured this view of an alien copper-colored Ring-World. The overexposed planet has deliberately been removed to show the unlit Rings alone, seen from an elevation of 60, the highest Cassini has yet attained.
The view is a mosaic of 27 images -- nine separate sets of red, green and blue images -- taken over the course of about 45', as Cassini scanned across the entire main Ring System. The Planet's shadow carves a dark swath across the Ring-Plane at the right.
Moons visible in this image: Epimetheus, at the 1 o'clock position; Pandora, at the 5 o'clock position and Janus, at the 10 o'clock position.
Bright clumps of material in the narrow F-Ring moved in their orbits between each of the color exposures, creating a chromatic misalignment that provides some sense of the continuous motion in the Ring System.
Radially extending lens flare artifacts, which result from light being scattered within the camera optics, are present in the view.
The images in this natural-color view were obtained with the Cassini spacecraft wide-angle camera on Jan. 21, 2007, at a distance of approx. 1,6 MKM (1 MMs) from Saturn. Image scale is 90 roughly Km (about 56 miles) per pixel".
MareKromium
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Saturn-PIA08362.jpgThe Ringed World, from above65 visiteCaption NASA:"Surely one of the most gorgeous sights the Solar System has to offer, Saturn sits enveloped by the full splendor of its stately Rings. Taking in the Rings in their entirety was the focus of this particular imaging sequence. Therefore, the camera exposure times were just right to capture the dark-side of its Rings, but longer than that required to properly expose the globe of sunlit Saturn. Consequently, the sunlit half of the Planet is overexposed.
Between the blinding light of day and the dark of night, there is a strip of twilight on the globe where colorful details in the atmosphere can be seen. Bright clouds dot the bluish-grey Northern Polar Region here. In the South, the Planet's night side glows golden in reflected light from the Rings' sunlit face.
Saturn's shadow stretches completely across the Rings in this view, taken on Jan. 19, 2007, in contrast to what Cassini saw when it arrived in 2004.
The view is a mosaic of 36 images -- that is, 12 separate sets of red, green and blue images -- taken over the course of about 2,5 hours, as Cassini scanned across the entire Main Ring System. This view looks toward the unlit side of the Rings from about 40 above the Ring-Plane.
The images in this natural-color view were obtained with the Cassini spacecraft wide-angle camera at a distance of approx. 1,23 MKM (about 764.000 miles) from Saturn. Image scale is roughly 70 Km (about 44 miles) per pixel".MareKromium
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Saturn-PIA08366.jpgSaturn and Rhea66 visiteCaption NASA:"A serene orb of ice is set against the gentle pastel clouds of giant Saturn. Rhea transits the face of the gas giant, whose darkened Rings and their planet-hugging shadows appear near upper right.
Rhea is the second largest of Saturn's moons.
This view looks toward the unilluminated side of the Rings from about 3 above the Ring-Plane.
Images taken using red, green and blue spectral filters were combined to create this natural color view. The view was acquired with the wide-angle camera on Feb. 4, 2007. Cassini acquired the view at a distance of approx. 1,2 MKM (about 700.000 miles) from Saturn and approx. 679.000 Km (about 422.000 miles) from Rhea.
Image scale is roughly 68 Km (about 42 miles) per pixel on Saturn and about 40 Km (about 25 miles) per pixel on Rhea".
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