Saturn: the "Ringed Beauty" and His Moons
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Saturn-PIA03559.jpgSaturn's clouds in 3D89 visiteSaturn's clouds and hazes at three different levels in the atmosphere are depicted in the image on the right, as observed by the visual infrared mapping spectrometer on the Cassini spacecraft.
In the image, red represents the deepest clouds yet found on Saturn. They are at an altitude where pressure is nearly double Earth's sea-level air pressure. The spectrometer saw these clouds using a 5.1 micron wavelength. Brightness levels in the original image were inverted to show cloud as bright features. Green is an image taken simultaneously at 1.6 micron wavelength, showing upper-level clouds near and above the altitude where atmospheric pressure equals Earth's sea-level air pressure, a pressure expressed as 1 bar. Blue is an image taken at 2.05 micron, a wavelength which is limited to showing only higher cloud level due to absorption of light by the hydrogen gas comprising the bulk of Saturn's atmosphere. Blue indicated clouds of an altitude where atmospheric pressure is only about 70 percent of Earth's sea-level air pressure. Thus, the aqua-colored feature over the equator is high-altitude haze residing 10 kilometers (6 miles) altitude above the typical zonal features seen in reflected sunlight over the planet (green).
The image on the left shows only the upperatmosphere above the 1-bar level, and is the view seen in reflected sunlight as observed by cameras not capable of seeing the thermal radiation of Saturn. Red in this image was taken at 2.79 micron, a wavelength that absorbs ammonia. The greenish appearance of the south pole indicates that ammonia gas is enhanced there.
As opposed to the uniform bands of hazes and clouds seen over the planet at pressures near and less than 1 bar, clouds at the 2-bar level (red, in right-hand image) are distinct, and come in a variety of shapes and sizes.
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Saturn-PIA06164-br500.jpgSaturn, Titan and Mimas in real colors78 visiteCaption NASA originale:"From its station nearly 1,2 BKMs (or 746 MMs) from Earth, the stalwart Cassini spacecraft sends holiday greetings to Earth with this lovely color portrait of Saturn and two of its moons. This color portrait serves as reminder of the Saturnian places we have already seen and the promise of future discovery at Titan when the European Space Agency's Huygens probe arrives at Titan on Jan. 14, 2005. A grayish, oval-shaped storm is visible in Saturn's southern hemisphere and is easily 475 Km across - the size of some hurricanes on Earth. Titan is visible near lower right with its thick, orange-colored atmosphere, and faint Mimas (398 Km across) appears just right of the rings' outer edge. Images taken in the red, green and blue filters with the Cassini spacecraft wide angle camera on Dec. 14, 2004, were combined to create this color view at a distance of approximately 719.000 Km from Saturn. The image scale is 43 Km (or 27 miles) per pixel".
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Saturn-PIA06177.jpgSaturn's Northern Hemisphere in natural colors62 visiteCaption NASA originale:"Saturn's Northern Hemisphere is presently a serene blue, more befitting of Uranus or Neptune, as seen in this natural color image from Cassini.
Light rays here travel a much longer path through the relatively cloud-free upper atmosphere. Along this path, shorter wavelength blue light rays are scattered effectively by gases in the atmosphere and it is this scattered light that gives the region its blue appearance. Why the upper atmosphere in the northern hemisphere is so cloud-free is not known, but may be related to colder temperatures brought on by the ring shadows cast there.
Shadows cast by the rings surround the pole, looking almost like dark atmospheric bands. The ring shadows at higher latitudes correspond to locations on the ringplane that are farther from the planet - i.e.: the northernmost ring shadow in this view is made by the outer edge of the A-Ring.
Spots of bright clouds also are visible throughout the region. This view is similar to an infrared image obtained by Cassini at nearly the same time".
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Saturn-PIA06194.jpgAre these "anomalies" the clock-tracks of a New Moon?76 visiteUna piccola premessa: le irregolarit fisiche del margine esterno dell'Anello A, situate in prossimit di quella zona conosciuta come Divisione Keeler (larga circa 42 Km), sono ritenute dalla NASA una evidenza indiretta (o prova circostanziale) dell'esistenza di una nuova 'luna nascosta'. In realt, queste alterazioni fisiche - le quali altro non sono che il riflesso visibile delle interazioni gravitazionali esercitate da corpi sufficientemente vicini - allorch i corpi interagenti sono, almeno relativamente, "stabili" (come dobbiamo ragionevolmente supporre che sia nel nostro caso), si caratterizzano per una sostanziale regolarit e ripetitivit. Ora nell'immagine di riferimento, come potete vedere Voi stessi, questa 'anomalia gravitazionale' sembra tutt'altro che regolare e ripetitiva. Perch non provare a pensare, dunque, ad una vera e propria 'interazione complessa' (possibile indice della presenza di pi lune) o, magari, a qualcosa di diverso (per esempio ad un - raro - Fenomeno Transitorio)?
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Saturn-PIA06196.jpgGravitational Anomalies and Interferences81 visiteIn fondo, per quanto ne sappiamo, i Fenomeni Transitori non sono una prerogativa unica della superficie dei pianeti e non si manifestano solamente attraverso 'outgassing', 'annebbiamenti' e/o fenomeni luminosi! Anche i fenomeni gravitazionali possono essere transitori, allorch ci si trovi in un ambiente - per cos dire - "affollato" da corpi celesti, quale pu essere un'area di confine di uno degli Anelli di Saturno. Comunque eccoVi una parte della Caption NASA originale al riguardo:"Images taken of Saturn's rings by Cassini immediately after it entered orbit around Saturn have turned up circumstantial evidence that an unseen moon may be orbiting dead center in the narrow Keeler Gap in Saturn's outer A-Ring. Several faint discontinuities, or spikes, in the outer gap edge have been found in 2 narrow-angle camera images of the illuminated side of the Rings. These features are similar to the spikes protruding inward from the core of the F-Ring during Prometheus's passages and it is likely that the features are caused by the passages of a yet-unseen moonlet on an eccentric orbit within the Keeler gap".
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Saturn-PIA06436.jpgSaturn's Aurora75 visiteThe Cassini spacecraft has obtained new images of Saturn's auroral emissions, which are similar to Earth's Northern Lights. Images taken on June 21, 2005, with Cassini's UVA Imaging Spectrograph are the first 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 H gas excited by electron bombardment, while red-orange represents reflected sunlight. The images show that the aurora lights at the Polar Regions respond rapidly to changes in the Solar Wind. Previous images have been taken closer to the Equator, making it difficult to see the Polar Regions. Changes in the emissions inside the Saturn South-Pole aurora are visible by comparing the 2 images, taken about 1 hour apart. The brightest spot in the left aurora fades and a bright spot appears in the middle of the aurora in the second image. Like Earth's aurora, those on Saturn form in an oval at high latitudes around each pole, along with associated spots and streaks. The ultraviolet imaging spectrograph data shows that the Saturn aurora lasts at least one hour, but small changes are visible in that time between the two images.
The same process produces auroras on both planets: variations in the plasma environment release trapped electrons, which stream along the magnetic field lines into the upper atmosphere. There, they collide with atoms and molecules, exciting them to higher energies. The atoms and molecules release this added energy by radiating light at particular characteristic colors and wavelengths. On Earth, this light is mostly from oxygen atoms and nitrogen molecules. On Saturn, it is from emissions of molecular and atomic hydrogen.
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Saturn-PIA06485_modest.jpgSaturn, Janus and Mimas (in natural colors)67 visiteCaption NASA originale:"Looking something like the fibrous bow of a violin, Saturn's colorful rings sweep through this spectacular natural color view while two small moons look on.
From left, the moons visible here are Janus (181 Km across) and Mimas (398 Km across). Cassini's view in this image is from beneath the ring plane; the moons are on the far side of Saturn. Janus leads Mimas as the two moons orbit the planet. Nearly the entire ring system can be seen in this view. The diaphanous C-Ring appears at the upper right, followed by the multi-hued B-Ring. Next, the famous Cassini division (4.800 Km wide) separates the A and B rings. The outer edge of the B-Ring which forms the inner boundary of the Cassini division is maintained by a gravitational resonance with Mimas. Near the outer edge of the A-Ring are the Encke Gap (325 Km wide) and the barely visible Keeler Gap (35 Km wide). The faint, thread-like F-Ring is slightly discernible just beyond the main rings".
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Saturn-PIA06491_modest.jpgSaturn's swirls and ribbons75 visiteCaption NASA originale:"This Cassini image shows mesmerizing detail in the swirls and ribbons of air in Saturn's atmosphere. The view was obtained at a distance of 8.5 million Km from Saturn and is but a taste of what the spacecraft's powerful cameras will show when Cassini draws nearer to the planet. The limb of the planet is visible at lower right.
The image was taken with the Cassini spacecraft narrow angle camera on Sept. 15, 2004, through a filter sensitive to wavelengths of infrared light. The image scale is 101 Km per pixel. The image was magnified by a factor of two and slightly contrast enhanced to improve visibility of features in the atmosphere".
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Saturn-PIA06532_modest.jpgSaturn from 618.000 Km67 visiteCaption NASA originale:"Cassini pierced the ring plane and rounded Saturn on Oct. 27, 2004, capturing this view of the dark portion of the rings. A portion of the planet's atmosphere is visible here, as is its shadow on the surface of the rings.
The image was taken with the Cassini spacecraft wide angle camera on Oct. 27, 2004, at a distance of about 618.000 Km from Saturn through a filter sensitive to wavelengths of infrared light centered at 1001 nanometers. The image scale is 33 Km per pixel".
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Saturn-PIA06538_modest.jpgSaturn and the shadow of his Rings67 visiteThis majestic view of Saturn captures several phenomena of interest to scientists working on the Cassini mission. The planet's nighttime atmosphere looms ahead - an excellent place to search for storms and lightning. Saturn's shadow stretches across the rings, which will over the next four years receive their most thorough examination since Galileo discovered them in 1610. And barely visible near lower right just inside the F-Ring, is the small shepherd moon Prometheus (102 Km across). Researchers will explore the many moons of Saturn, including special ones like Prometheus that help maintain some of the rings and gaps in this complex and dynamic system.
The image was taken in visible light with the Cassini spacecraft wide angle camera on Oct. 29, 2004, at a distance of about 940.000 Km from Saturn. The image scale is 52 Km per pixel."
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Saturn-PIA06604.jpgSaturn, Titan, Rhea and Enceladus67 visiteCaption NASA originale:"Saturn's biggest and brightest moons are visible in this portrait by Cassini.
Titan (5.150 Km, or 3,200 miles across) is Saturn's largest moon and appears at the lower left. Note that some details in the moon's smoggy atmosphere are visible here. Rhea (1.528 Km, or 949 miles across) is the planet's second largest moon and is seen above center. Enceladus (505 Km, or 314 miles across) has the brightest surface in the solar system, reflecting nearly all of the sunlight that falls upon it. Enceladus is just above the rings, left of center. Titan was on the far side of the planet at the time of this exposure, while the other moons were on the near side, much closer to Cassini.
Also seen here are details in the cloud bands of Saturn's mostly hydrogen atmosphere, variations in brightness across the dazzling rings and magnificent ring shadows cast upon the northern hemisphere. The image was taken with the Cassini spacecraft wide-angle camera on Feb. 5, 2005, at a distance of approximately 3.4 million kilometers (2.1 million miles) from Saturn through a filter sensitive to wavelengths of infrared light centered at 728 nanometers. The image scale is 200 kilometers (124 miles) per pixel".
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Saturn-PIA06619.jpgThe Southern Side of Saturn77 visiteCaption NASA originale:"Viewed nearly edge-on, Saturn's rings appear dark and pencil-thin against the backdrop of the planet's swirling clouds. Notable here are the shadows cast by the rings onto the northern hemisphere, as well as details of the banded atmosphere, such as the bright equatorial region. The image was taken with the Cassini spacecraft wide-angle camera on Feb. 18, 2005, at a distance of approximately 1,2 MKM from Saturn through a filter sensitive to wavelengths of infrared light centered at 727 nnmts, where gaseous methane absorbs. The image scale is 67 Km per pixel".
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