Saturn: the "Ringed Beauty" and His Moons |
 |
| TITOLO |
+ |
- |
| NOME FILE |
+ |
- |
| DATA |
+ |
- |
| POSIZIONE |
+ |
- |
|
|
Enceladus (1)42 visteA 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. This is a story that is recounted by imaging scientists in a paper published in the journal Science on March 10, 2006.
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.
Ancient craters remain somewhat pristine in some locales, but have clearly relaxed in others. Northward-trending fractures, likely caused by a change in the moon's rate of rotation and the consequent flattening of the moon's shape, rip across the southern hemisphere. The South Polar terrain is marked by a striking set of 'blue' fractures and encircled by a conspicuous and continuous chain of folds and ridges, testament to the forces within Enceladus that have yet to be silenced.
|
|
Enceladus' Geysers Model28 visteAs Saturn's active moon Enceladus continues to spew icy particles into space, scientists struggle to understand the mechanics of what is going on beneath the fractured south polar terrain. This graphic illustrates key aspects of the model proposed by the Cassini imaging science team in a paper published in the journal Science on March 10, 2006.
The model shows how proposed underground reservoirs of pressurized liquid water above 273 degrees Kelvin (0° Celsius) could fuel geysers that send jets of icy material into the skies above the moon's south pole. In the graphic, the vent to the surface pierces one of the "tiger stripe" fractures seen in Cassini views of the Southern Polar Terrain. Temperatures increase with depth.
Some combination of internal radioactive decay and flexing--perhaps concentrated within the tiger stripe fractures and brought about by the particular characteristics of Enceladus' orbit--is implicated as the source of the heat creating the liquid reservoirs. However, it is not yet clear how the deep interior of Enceladus functions, nor whether the moon is fully differentiated (separated into layers, with rock at the center and ice outside).
|
|
Enceladus' active South Pole (1)33 vistePlumes of icy material extend above the Southern Polar Region of Enceladus, as imaged by the Cassini spacecraft in February 2005. The monochrome view is presented along with a color-coded version on the right. The latter reveals a fainter and much more extended plume component.
Images like these are being analyzed by scientists as they seek to explain the processes that could be producing such incredible features. As reported in the journal Science on March 10, 2006, imaging scientists believe that the plumes are geysers erupting from pressurized subsurface reservoirs of liquid water above 273 degrees Kelvin (0° C.).
Another plume view was taken 1 month earlier and looks broadside at the moon's prominent "Tiger Stripe" fractures. In the January view, the plume appears to have a single component. The February view looks along the Tiger Stripe fractures and reveals both a large and a small component to the plume; the smaller, fainter component is separated from the main plume by about 100 Km.
|
|
Enceladus' surface temperatures (2)29 visteEnhanced thermal emission is seen in the vicinity of the prominent "Tiger Stripe" fissures discovered by the imaging cameras.
In these images, the excess emission is most strongly seen in the left-most composite Infrared Spectrometer field of view, which includes a fissure near the end of one of the Tiger Stripes. The peak temperatures, 86 and 90 Kelvin (such as about -305 and -298 Fahrenheit) respectively, are averages over the Composite Infrared Spectrometer field of view, and other composite Infrared Spectrometer data suggest that much higher temperatures, up to at least 145 Kelvin (such as -199 Fahrenheit), occur in narrow zones a few hundred meters wide along the Tiger Stripe fissures.
The 1st image is centered near long. 135° W. and lat. 65° S. and each square from the composite infrared spectrometer field of view is about 17,5 Km (approx. 10,9 miles) across.
The 2nd image was taken nearly 3 times closer to Enceladus and is centered near long. 120° W, lat. 82° S.
|
|
Enceladus' surface temperatures (1)38 visteThe exciting mystery of an active South Polar Region on Saturn's icy moon Enceladus continues to unfold as scientists make the correlation between geologically youthful surface fractures and unusually warm temperatures.
This view shows excess heat radiation from cracks near the moon's South Pole. These warm fissures are the source of plumes of dust and gas seen by multiple instruments on the Cassini spacecraft during its flyby of Enceladus on July 14, 2005, as described in a series of papers in the March 10, 2006, issue of the journal Science. This image shows two arrays of temperature readings across the surface of Enceladus, as measured by the Cassini Composite Infrared Spectrometer (CCIS), superimposed on images of the surface taken simultaneously by the Imaging Science Subsystem. Surface temperatures in Kelvin, derived from the intensity of infrared radiation detected by the composite infrared spectrometer, are shown along with their formal uncertainties, although true uncertainties for temperatures below about 75 Kelvin (minus 325 degrees Fahrenheit) are not easily described by a single number.
|
|
The "Fountains" of Enceladus28 visteA fine spray of small, icy particles emanating from the warm, geologically unique province surrounding the South Pole of Enceladus was observed in a Cassini narrow-angle camera image of the crescent moon taken on Jan. 16, 2005. Taken from a high phase angle of 148° - a viewing geometry in which small particles become much easier to see - the plume of material becomes more apparent in images processed to enhance faint signals.
Imaging scientists have measured the light scattered by the plume's particles to determine their abundance and fall-off with height. Though the measurements of particle abundance are more certain within 100 Km of the surface, the values measured there are roughly consistent with the abundance of water ice particles made by other Cassini instruments (reported in 09/2005) at altitudes as high as 400 Km above the surface.
At present, it is not clear if the plume particles emanating from the south pole arises because of water vapor escaping from warm ice that is exposed to the surface. Another possibility is that at some depth beneath the surface, the temperatures are hot enough for water to become liquid, which then, under pressure, escapes to the surface like a cold Yellowstone geyser.
The image at the left was taken in visible green light. A dark mask was applied to the moon's bright limb to make the plume feature easier to see.
The image at the right has been color-coded to make faint signals in the plume more apparent. Images of other moons, such as Tethys and Mimas, taken in the last 10 months from similar lighting and viewing geometries, and with identical camera parameters, were closely examined to demonstrate that the plume towering above Enceladus' south pole is real and not a camera artifact.
The images were acquired at a distance of about 209,400 kilometers (130,100 miles) from Enceladus. Image scale is about 1 kilometer (0.6 mile) per pixel.
|
|
The "Fountains" of Enceladus26 viste"...this greatly enhanced and colorized image shows the enormous extent of the fainter, larger-scale component of the plume..."
Nota: dal tenore del commento NASA, oltre ad una leggera sorpresa, non pare trasparire alcunchè. Allora: se abbiamo capito bene c'è qualcosa che viene "spruzzato" nel cielo dalla superficie di Encelado e che forma una sorta di "fontana" di corpuscoli che si disperdono nello spazio.
Qualcosa di incredibile e di assolutamente "alieno" (nel senso di lontano dal nostro modo di vedere e di immaginare le cose) sta accadendo, ma la NASA si limita a darci un commentino secco e asciutto, come la risposta ad un quesito di Scienze Planetarie che verrebbe data al Professore da uno studente non troppo preparato. Abbiamo letto, recentemente, della costante caduta di interesse da parte dell'opinione pubblica in generale e dei giovani in particolare verso lo Spazio e l'esplorazione del Sistema Solare. Onestamente, visto l'atteggiamento costantemente bolso di ESA e NASA, non ce ne meravigliamo...
|
|
The "Fountains" of Enceladus28 visteRecent Cassini images of Saturn's moon Enceladus backlit by the sun show the fountain-like sources of the fine spray of material that towers over the South Polar Region. This image was taken looking more or less broadside at the "tiger stripe" fractures observed in earlier Enceladus images. It shows discrete plumes of a variety of apparent sizes above the limb of the moon.
|
|
Enceladus: a VERY active moon... (2)25 visteWrinkles and cracks have reworked the surface of Enceladus, perhaps due to the influence of tidal stresses. The monochrome view also makes it clear that certain geological provinces on the moon have been altered by the activity, erasing ancient craters, while other places have retained much of the cratering record.
The terrain seen here is on the Trailing Hemisphere of Enceladus; North is up.
This image was taken using a near infrared spectral filter sensitive to wavelengths of light centered at 752 nnmts. The view was obtained using the Cassini spacecraft narrow-angle camera on Jan. 17, 2006 at a distance of approx. 153.000 Km (about 95.000 miles) from Enceladus and at a phase angle of 29°. Image scale is about 912 mt (such as approx. 2.994 feet) per pixel.
Nota: i 4 Giganti Gassosi (Giove, Saturno, Urano e Nettuno) sono mondi circondati da tante lune, alcune delle quali ancora geologicamente attive, a dispetto delle loro dimensioni e della enorme - e via-via crescente - distanza di questi Sistemi dal Sole. Pensate, p.e., ad Io ed Europa (per Giove); a Titano ed Encelado (per Saturno) ed infine ad Ariel (per Urano) e Tritone (per Nettuno). I piccoli mondi rocciosi, invece, hanno poche lune (o nessuna, come Venere e Mercurio) e queste lune NON sembrano - il dubitativo è d'obbligo - essere geologicamente attive. Il caso del Sistema Multiplo di Plutone va trattato a parte. Tutto ciò premesso, che cosa si può dedurre? Forse che la "Gioventù Geologica" di una piccolo pianeta roccioso (una "luna") dipende anche dalle caratteristiche del suo "Mondo Madre"? I 4 Giganti Gassosi emettono enormi quantitativi di radiazioni e posseggono caratteristiche tali da farli rassomigliare, ora più ed ora meno, a piccole "stelle mancate": questa circostanza potrebbe avere un peso?
|
|
Enceladus: a VERY active moon... (1)23 visteA false color look reveals subtle details on Enceladus that are not visible in natural color views. The now-familiar bluish appearance (in false color views) of the Southern "Tiger Stripes" features and other relatively youthful fractures is almost certainly attributable to larger grain sizes of relatively pure ice, compared to most surface materials.
On the Tiger Stripes, this coarse-grained ice is seen in the colored deposits flanking the fractures as well as inside the fractures. On older fractures in other areas of Enceladus, the blue ice mostly occurs on the exposed wall scarps.
The color difference across the moon's surface (a subtle gradation from upper left to lower right) could indicate broad-scale compositional differences across the moon's surface. It is also possible that the gradation in color is due to differences in the way the brightness of Enceladus changes toward the limb, a characteristic which is highly dependent on wavelength and viewing geometry.
|
|
The "Young Face" of Enceladus19 visteOriginal caption:"For Enceladus, wrinkles mean the opposite of old age. This view of a crescent Enceladus shows a transition zone between a wrinkled and presumably younger Region of terrain and an older, more heavily cratered Region. The moon's geologically active Southern Polar Region is seen on the left.
The lit terrain shown here is on the side of Enceladus that faces away from Saturn.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Dec. 24, 2005 at a distance of approx. 108.000 Km (such as about 67.000 miles) from Enceladus, at a Sun-Enceladus-spacecraft angle of 102°.
Image scale is roughly 646 mt (about 2.118 feet) per pixel".
|
|
Enceladus over the B-Ring18 visteOriginal caption:"The moon Enceladus seems to hover above the outer reaches of Saturn's B-Ring. Below and to the right of Enceladus, four faint bands lie in the center of the dark Cassini Division.
Recently, scientists have speculated that the particles that make up the dense B and A-Rings might be more like fluffy snowballs than hard ice cubes. The conclusion is based on temperature data obtained by the Cassini spacecraft.
Enceladus' diameter is about 505 Km (such as approx. 314 miles). The icy moon is on the near side of the Rings in this view.
This image was taken in visible light with the Cassini spacecraft narrow-angle camera on Sept. 15, 2005, at a distance of approx. 2,3 MKM (1,4 MMs) from Enceladus.
The image scale is 14 Km (approx. 9 miles) per pixel on Enceladus".
|
|
| 2537 files su 212 pagina(e) |
|
|
|
|
|
|
|
174 | |
|
|
|
|
|
