| Piú viste - Neptune and His Moons |
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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s Rings-PIA02207_modest.jpgNeptune's Rings (and a crescent Neptune) from 1,1 MKM55 visiteCaption NASA originale:"This wide-angle Voyager 2 image, taken through the camera's clear filter, is the first to show Neptune's rings in detail. The 2 main rings, about 53.000 Km and 63.000 Km from Neptune, are 5 to 10 times brighter than in earlier images and the difference is due to lighting and viewing geometry. In approach images, the rings were seen in light scattered backward toward the spacecraft at a 15° phase angle. However, this image was taken at a 135° phase angle as Voyager 2 left the planet. That geometry is ideal for detecting microscopic particles that forward-scatter light preferentially. The fact that Neptune's Rings are so much brighter at that angle means the particle-size distribution is quite different from most of Uranus' and Saturn's rings, which contain fewer dust-size grains. However, a few components of the Saturnian and Uranian ring systems exhibit forward-scattering behavior: the F-Ring and the Encke Gap ringlet at Saturn, and 1986U1R at Uranus".
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Triton-PIA01538_modest.jpgGeologic processes on Triton (2)55 visiteCaption NASA originale:"Part of the complex geologic history of icy Triton, Neptune's largest satellite, is shown in this Voyager 2 photo, which has a resolution of 900 meters (2.700 feet) per picture element. The photo was received as part of a Triton-mapping sequence between 3:30 and 5:30 a.m. (PDT). This view is about 500 Km (300 miles) across.
It encompasses 2 depressions, possibly old impact basins, that have been extensively modified by flooding, melting, faulting and collapse. Several episodes of filling and partial removal of material appear to have occurred. The rough area in the middle of the bottom depression probably marks the most recent eruption of material. Only a few impact craters dot the area, which shows the dominance of internally driven geologic processes on Triton".
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Triton-PIA01537_modest.jpgGeologic processes on Triton (1)55 visiteCaption NASA originale:"This image of Triton was taken from a distance of about 130.000 Km (80.000 miles) at 12:20 a.m. PDT Aug. 25 1989. The image was received at JPL four hours later at about 4:20 a.m. The smallest detail that can be seen is about 2,5 Km (or 1,5 miles) across. The long linear feature extending vertically across the image is probably a graben (a narrow down dropped fault block) about 35 Km (20 miles) across. The ridge in the center of the graben probably is ice that has welled up by plastic flow in the floor of the graben. The surrounding terrain is a relatively young icy surface with few impact craters".
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Triton-PIA00061_modest.jpgTriton's Northern Hemisphere in HR55 visiteCaption NASA originale:"This is one of the most detailed views of the surface of Triton taken by Voyager 2 on its flyby of the large satellite of Neptune early in the morning of Aug. 25, 1989. The picture was stored on the tape recorder and relayed to Earth later. Taken from a distance of only 40.000 Km (25.000 mi), the frame is about 220 Km (140 miles) across and shows details as small as 750 meters (0.5 miles). Most of the area is covered by a peculiar landscape of roughly circular depressions separated by rugged ridges. This type of terrain, which covers large tracts of Triton's Northern Hemisphere, is unlike anything seen elsewhere in the Solar System. The depressions are probably not impact craters: they are too similar in size and too regularly spaced. Their origin is still unknown, but may involve local melting and collapse of the icy surface. A conspicuous set of grooves and ridges cuts across the landscape, indicating fracturing and deformation of Triton's surface. The rarity of impact craters suggests a young surface by solar system standards, probably less than a few billion years old".
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Triton-PIA00059_modest.jpgThe South Polar Region of Triton: "dark plumes" and "seasonal winds"55 visiteCaption NASA originale:"This image of the South Polar terrain of Triton, taken on Aug. 25, 1989 reveals about 50 dark plumes or 'wind streaks' on the icy surface. The plumes originate at very dark spots generally a few miles in diameter and some are more than 100 miles long. The spots which clearly mark the source of the dark material may be vents where gas has erupted from beneath the surface and carried dark particles into Triton's nitrogen atmosphere. Southwesterly winds then transported the erupted particles, which formed gradually thinning deposits to the northeast of most vents. It is possible that the eruptions have been driven by seasonal heating of very shallow subsurface deposits of volatiles and the winds transporting particles similarly may be seasonal winds. The polar terrain, upon which the dark streaks have been deposited, is a region of bright materials mottled with irregular, somewhat dark patches. The pattern of irregular patches suggests that they may correspond to lag deposits of moderately dark material that cap the bright ice over the polar terrain".
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Neptune-crescent-PIA02204_modest.jpgNeptune's bright crescent55 visiteCaption NASA originale:"Neptune's bright crescent taken in six filters (from bottom to top: UV, violet, blue, clear, green, orange) on August, 31, 1989. The images were shuttered in temporal order: violet, blue, UV, clear, green, orange. These images how the bright core of D2, the South Polar feature, and the symmetric structure immediately surrounding the South Pole. The relatively high contrast of the features in these images indicates that they extend above most of the scattering haze and absorbing methane gas in Neptune's atmosphere. [Image processing by D.A. Alexander]"
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Proteus2.jpgProteus (HR)55 visitenessun commento
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Nereid-CJH.gifNereid55 visiteNereid was discovered in 1949 by astronomer Gerard Kuiper. Nereid is about 340 Km (210 miles) in diameter and is so far from Neptune that it requires 360 days to make one orbit. Voyager's best photos of Nereid were taken from about 4,7 MKM (about 2,9 MMs). The photos show that the moon's surface reflects about 14% of the sunlight that strikes it, making it somewhat more reflective than Earth's Moon and more than twice as reflective as Proteus. Nereid's orbit is the most eccentric in the Solar System. Its distance to Neptune ranges from about 1.353.600 Km (about 841.100 miles) to 9.623.700 Km (such as about 5.980.200 miles).
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ZA-U-Triton.jpgFarewell Triton... (HR)55 visitenessun commento
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Triton-PIA01994.jpgStrange "surface features" on Triton (clouds?!?)55 visiteCaption NASA originale"Already intriguing patterns of unknown origin appear on the surface of Neptune's largest satellite, Triton, in this image returned by Voyager 2. The image was taken Aug. 22, 1989, from a distance of about 4 MKM (approx. 2.5 MMs). Voyager images show that Triton's diameter is about 2.720 Km (approx. 1.690 miles) and that it is one of the brightest objects in the Solar System, reflecting about 70% of the sunlight that strikes it. This is the Hemisphere of Triton that always faces away from Neptune. The South Pole is near the bottom of the image. Triton's rotation axis is tilted so that the latitude at the center of the disk is 55° South. Dark regions at the top of the disk extend from roughly the equator to beyond 20° North. The margin between the bright and dark regions varies with longitude around the satellite. The gray, featureless area just to the right of the center of the disk is due to a reseau (reticule mark) in the camera".
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