| Piú viste - Neptune and His Moons |
ZC-Neptune_s Rings-PIA01493_modest.jpgThe Rings of Neptune56 visiteCaption NASA originale:"In Neptune's outermost ring, 39.000 miles out, material mysteriously clumps into 3 arcs.
Voyager 2 acquired this image as it encountered Neptune in August 1989".
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Neptune and Triton - PIA01491_modest.jpgNeptune and Triton56 visiteCaption NASA originale:"This image was returned by the Voyager 2 spacecraft on July 3, 1989, when it was 76 MKM from Neptune. The planet and its largest satellite, Triton, are captured in the field of view of Voyager's narrow-angle camera through violet, clear and orange filters. Triton appears in the lower right corner at about 5 o'clock relative to Neptune.
Recent measurements from Voyager images show Triton to be between 1.400 and 1.800 Km in radius with a surface that is about as bright as freshly fallen snow".
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Triton-PIA02246_modest.jpgTriton from Voyager 2 (real colors)56 visiteCaption NASA originale:"Features as small as 100 Km across can be seen in this color image of Neptune's satellite Triton, photographed by Voyager 2 on Aug. 20, 1989, while it was still 5.4 MKM (3.3 million miles) from Neptune. Triton's overall pinkish color may be due to reddish materials produced by irradiation of methane gas and ice on the satellite. The dark areas near the top of the image seem to be part of a belt of dark markings observed near Triton's equator at different longitudes. Generally, darker areas on Triton appear to be somewhat redder in color than brighter areas. The central longitude in the image is 123°. Here the south pole is at about 6 o'clock, approximately one sixth of the way up from the bottom. The color image was made from three black and white frames, taken through clear, violet and green filters".
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Triton-PIA00317_modest.jpgTriton (False Colors; credits: NASA/JPL/USGS)56 visiteCaption NASA originale:"The color was synthesized by combining HR images taken through orange, violet and ultraviolet filters; these images were displayed as red, green and blue images and combined to create this color version. With a radius of 1.350 Km, about 22% smaller than Earth's Moon, Triton is by far the largest satellite of Neptune. It is 1 of only 3 objects in the Solar System known to have a nitrogen-dominated atmosphere (the others are Earth and Saturn's giant moon, Titan). Triton has the coldest surface known anywhere in the Solar System (38 K, about -391 degrees F); it is so cold that most of Triton's nitrogen is condensed as frost, making it the only satellite in the Solar System known to have a surface made mainly of nitrogen ice. The pinkish deposits constitute a vast south polar cap believed to contain methane ice, which would have reacted under sunlight to form pink or red compounds. The dark streaks overlying these pink ices are believed to be an icy and perhaps carbonaceous dust deposited from huge geyser-like plumes, some of which were found to be active during the Voyager 2 flyby. The bluish-green band visible in this image extends all the way around Triton near the equator; it may consist of relatively fresh nitrogen frost deposits. The greenish areas includes what is called the cantaloupe terrain, whose origin is unknown, and a set of "cryovolcanic" landscapes apparently produced by icy-cold liquids (now frozen) erupted from Triton's interior".
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Triton-PIA00056_modest.jpgTriton's limb56 visiteCaption NASA originale:"Voyager 2 acquired this black and white image of Triton, Neptune's largest satellite, during the night of Aug. 24-25, 1989. Triton's limb cuts obliquely across the middle of the image. The field of view is about 1.000 Km (600 miles) across. Three irregular dark areas, surrounded by brighter material, dominate the image. Low-lying material with intermediate albedo occupies the central area, and fresh craters occur along the right margin. Sub-parallel alignment of linear patches of dark material shown in the lower and left part of the image suggests that the patches are structurally controlled".
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Neq-Neptune-PIA00057.jpgThe "haze" of Neptune (false colors)56 visiteCaption NASA originale:"This false color photograph of Neptune was made from Voyager 2 images taken through 3 filters: blue, green and a filter that passes light at a wavelength that is absorbed by methane gas. Thus, regions that appear white or bright red are those that reflect sunlight before it passes through a large quantity of methane. The image reveals the presence of a ubiquitous haze that covers Neptune in a semitransparent layer. Near the center of the disk, sunlight passes through the haze and deeper into the atmosphere, where some wavelengths are absorbed by methane gas, causing the center of the image to appear less red. Near the edge of the Planet, the haze scatters sunlight at higher altitude, above most of the methane, causing the bright red edge around the planet. By measuring haze brightness at several wavelengths, scientists are able to estimate the thickness of the haze and its ability to scatter sunlight. The image is among the last full disk photos that Voyager 2 took before beginning its endless journey into interstellar space".
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Neptune-shadows-PIA02220.jpg"Cloud shadows" on Neptune56 visiteCaption NASA originale:"This image of Neptune shows the discovery of shadows in Neptune's atmosphere, shadows cast onto a deep cloud band by small elevated clouds. They are the first cloud shadows ever seen by Voyager 2 on any planet. Estimates of the height of these discrete clouds above the underlying cloud bank can be obtained by careful analysis of this data".
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Triton-PEI.jpgMoments of Triton...56 visiteThis set of images shows the best views of Neptune's moon Triton taken by Voyager 2 as the spacecraft withdrew from the Neptune system on August 25, 1989. The top four images were constructed from various color image bands as Voyager receded from Triton.
The third image from the left is sharper than the other four, because it was taken with the Narrow Angle Camera, with Triton filling two thirds of the frame. The thin crescent first image, while much closer, spanned about a quarter of the frame. The second image was somewhat smaller, and the last was very small. The first of the four images was composed of Blue, Green, and Orange filter images. The second utilized Violet, Green, and Orange Filtered images. In both composites, the Orange image was of poorer quality. In the fourth image, no orange was available, and the green and blue images were badly smeared, though somewhat salvageable. A clear filtered image (also smeared) was substituted for orange. They were combined and used as a color overlay for a slightly overexposed, but sharp clear filtered view. The third image is composed of a Violet and a Green wide-angle image. Like all the images in the first and second composites, and like the images used to color the fourth composite, these images were underexposed. However, they were very sharp. The orange image came from a poor quality wide angle orange image. The resulting color image was combined with a well exposed clear filter image to provide the detail
The Narrow Angle images used in these mosaics were the first obtained after closest approach, with the exception of a single clear filter image obtained while the disk was about twice as big as what could be framed in the camera's field of view. It is very noisy, and by far the worst underexposure of them all, and could not be processed to the point in which the whole image could be made presentable. However, a few sections were salvaged. The first (lower left) was binned to make up for noisiness and sharpened. It was then merged with the color data from the third image above. A cloud can be seen near the limb. To its right is an image of the cloud that has not been as heavily processed. The cloud itself is better presented, as it was far brighter than the surrounding area and hence more securely detected. Its shadow can be faintly made out to its right.
The next two images are the same, but one to the right was merged with color data. The image is towards the center of the crescent, the brightest area, in which white spots can be seen. Although a few of them may be impact craters, this area, as most of the crescent, is over the south polar cap, and thus frost covered, and the appearance of this area most closely resembles the cantaloupe terrain seen on the other hemisphere before closest approach. The final image (lower right) hints of surface topography near the terminator. It seems it is one of the more rugged parts of Triton. The large, foreshortened circular feature slightly below the center of the image is a dimple similar those found in the cantaloupe terrain. The other features are too ambiguous to determine whether or not they are of the same nature.
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Neptune-PIA02245.jpgNeptune from 16.000.000 Km55 visiteCaption NASA originale:"This color image, produced from a distance of about 16 MKM, shows several complex and puzzling atmospheric features. The Great Dark Spot (GDS) seen at the center is about 13.000 Km by 6.600 km in size - as large along its longer dimension as the Earth. The bright, wispy "cirrus-type" clouds seen hovering in the vicinity of the GDS are higher in altitude than the dark material of unknown origin which defines its boundaries".
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Triton-PIA02213_modest.jpgThe limb of Triton (natural colors - elab. NASA)55 visiteCaption NASA originale:"This natural color image of the limb of Triton was taken early in the morning of Aug. 25, 1989, when the Voyager 2 spacecraft was at a distance of about 210.000 Km (128.000 miles) from the icy satellite. The largest surface features visible area about 3 miles across. The picture is a composite of images taken through the violet, green and clear filters.
The image shows a geologic boundary between a rough, pitted surface to the right and a smoother surface to the left".
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ZA-Neptune_s Rings-PIA02202_modest.jpgThe Rings of Neptune (full system) 255 visiteCaption NASA originale:"This pair of Voyager 2 images (FDS 11446.21 and 11448.10), two 591-s exposures obtained through the clear filter of the wide angle camera, show the full ring system with the highest sensitivity. Visible in this figure are the bright, narrow N53 and N63 rings, the diffuse N42 ring, and (faintly) the plateau outside of the N53 ring (with its slight brightening near 57.500 Km)".
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Nereid-V2-PIA00054.jpgNereid55 visiteUn'immagine certo non magnifica, ma di grande valore e molto rara: si tratta di Nereide, la seconda delle due Lune Maggiori di Nettuno. I dettagli che possono percepirsi da questa fotografia ottenuta dal Voyager 2 sono troppo indefiniti per poter azzardare delle valutazioni, ma l'ipotesi più probabile relativamente alle fattezze di Nereide, è che si tratti di un piccolo mondo fatto di roccia e ghiaccio, dalla forma irregolare, ricoperto di crateri da impatto e costellato da crepacci che ne rendono la superficie completamente inospitale.
Forse, come sostengono alcuni Scienziati, si potrebbe trattare di un KBO catturato da Nettuno in tempi assai remoti.
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