| Piú viste - Neptune and His Moons |
Neptune-South_Hem-V2-PIA00050_modest.jpgThe Southern Polar Region of Neptune from approx. 4.200.000 Km74 visiteGli Scienziati, analizzando le immagini fornite dalla Sonda Voyager 2, si sono convinti che il sistema atmosferico di Nettuno sia molto simile a quello di Giove: queste grandi formazioni nuvolose bianche riprese dalle fotocamere della Sonda si formano, al pari dei venti che le sospingono, nelle zone equatoriali del Pianeta. Poi, spostandosi verso Sud, questi venti diventano sempre pił veloci e violenti. Un sistema configurato in maniera interessante ma, probabilmente, piuttosto instabile.
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Z-Thalassa.gifThalassa74 visiteThalassa appears to be about 80 Km (about 50 miles) in diameter.
It orbits Neptune in 7 hours and 30 minutes, about 25.200 Km (such as approx. 15.700 miles) above the cloud tops. It is irregularly shaped and shows no sign of any geological modification. Thalassa circles the Planet in the same direction as Neptune rotates. This image has been slightly smeared so that Thalassa appears highly elongated.
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Triton-PIA02234.jpgTriton, from 530.000 Km!74 visiteCaption NASA:"Voyager 2 was 530.000 Km (330,000 miles) from Neptune's largest satellite, Triton, when this photo was taken, Aug. 24, 1989. With a resolution of 10 Km (about 6 miles), this is the first photo of Triton to reveal surface topography. The South Pole, continuously illuminated by sunlight at this season, is at bottom left. The boundary between the bright Southern Hemisphere and the darker Northern Hemisphere is clearly visible. Both the darker regions to the north and the very bright sub-equatorial band show a complex pattern of irregular topography that somewhat resembles "fretted terrain" on parts of Venus and Mars.
The pattern of dark and light Regions over most of the Southern Hemisphere will require HR images for interpretation. Also evident are long, straight lines that appear to be surface expressions of internal, tectonic processes. No large impact craters are visible, suggesting that the crust of Triton has been renewed relatively recently that is, within the past billion years or less".MareKromium
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Triton-PIA12187.jpgTritonian Terminator74 visitenessun commentoMareKromium
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Neptune-PIA01998.jpgNeptune, from FAR away...73 visiteCaption NASA originale:"This image of Neptune was taken through the clear filter of the narrow-angle camera, when the Voyager 2 spacecraft was at a range of 57 MKM (about 35 MMs). The image was processed by computer to show the newly resolved dark oval feature embedded in the middle of the dusky southern collar. The large dark spot nearer the equator is also prominent on the left edge of the disk. The new small dark spot rotates faster than the large dark spot indicating that the winds on Neptune have different velocities at different latitudes as is the case for Jupiter, Saturn and Uranus".
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Triton-vg2_p34665.jpgTriton (in natural colors and HR)73 visitenessun commento
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ZA-Neptune_s Rings-PIA01997_modest.jpgThe Rings of Neptune (full system) 172 visiteCaption NASA originale:"These two 591-second exposures of the rings of Neptune were taken with the clear filter by the Voyager 2 wide-angle camera on Aug. 26, 1989 from a distance of 280.000 Km (175.000 miles). The 2 main rings are clearly visible and appear complete over the region imaged. The time between exposures was 1 hour and 27 minutes. [During this period the bright ring arcs in the outer bright ring were not visible in either picture (they were unfortunately on the opposite side of the planet for each exposure).] Also visible in this image is the inner faint ring at about 42.000 km (25.000 miles) from the center of Neptune and the faint band which extends smoothly from the 53.000 Km (33.000 miles) ring to roughly halfway between the 2 bright rings".
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Nereid-vg2_1138148.jpgNereid (HR)72 visitenessun commento
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Neptune-newmoons-PIA01991.jpgNew moons of Neptune70 visiteThis image captured by the Voyager 2 was used to confirm the discovery of 3 new moons orbiting Neptune. The 46" exposure was taken by Voyager 2's narrow angle camera through a clear filter on July 30, 1989, when the spacecraft was about 37,3 MKM (or 23,6 MMs) from Neptune. The large globe of the planet itself is severely overexposed and appears pure white. The image has been computer processed to accentuate the new moons, which otherwise would appear little stronger than background noise. The satellite 1989 N1, at right in this frame, was discovered by Voyager 2 in early July 1989. The new satellites are 1989 N2, 1989 N3 and 1989 N4. Each of the moons appears as a small streak: an effect caused by movement of the spacecraft during the long exposure. The new moons occupy nearly circular and equatorial orbits ranging from about 27.300 to 48.300 Km (such as 17.000 to 30.000 miles) from Neptune's cloud tops, and are estimated to range in diameter from about 100 to 200 Km (such as 60 to 125 miles).
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Triton-PIA00329.jpgViews of Triton (natural colors - elab. NASA)70 visiteTriton Voyager 2 approach sequence with latitude-longitude grid superposed. The color image was reconstructed by making a computer composite of three black and white images taken through red, green and blue filters. Details on Triton's surface unfold dramatically in this sequence of approach images. South Pole near the bottom of the images at the convergence of lines of longitude. Resolution changes from about 60 Km/pixel (37 mi/pixel) in the image at upper left taken from a distance of 500.000 Km to about 5 Km/pixel (3,1 mi/pixel) for the image at lower right. Global and regional albedo features are visible in all of the images. The albedo features can be tracked in successive images and show that Triton has undergone about 3/4 of a rotation during the 4.3-day interval over which these images were obtained.
A Southern Polar Cap of bright pink, yellow and white materials covers nearly all of the Southern Hemisphere; these materials consist of Nitrogen ice with traces of other substances, including frozen CH4 and CO2. Feeble ultraviolet radiation from the Sun is thought to act on methane to cause chemical reactions to the pinkish yellowish substances. At the time of the Voyager 2 flyby (Jan. 1989) Triton's Southern Hemisphere was starting the Summer Season and the South Pole was canted toward the Sun day and night, such that the Polar Cap was sublimating under the relatively 'hot' summer Sun (surface temperature about 38 K, about -391 degree F). Numerous dark streaks on the Southern Polar Nitrogen-ice cap are thought to consist of dark dust deposited by prevailing winds in Triton's tenuous Nitrogen Atmosphere. A bluish band, seen in all of the images, nearly circumstances Triton's Equator; this band is thought to consist of fairly Nitrogen frost, perhaps deposited in the decade prior to Voyager 2's flyby.MareKromium
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Neptune-PIA01995.jpgSouth Polar Clouds and Shadows (Natural Colors; credits: Lunexit)70 visiteCaption NASA:"This image of Neptune's South Polar Region was obtained by the NASA Voyager 2 Probe narrow-angle camera on Aug. 23, 1989, when it was at a distance of about 25 MKM (about 1,6 MMs).
The smallest cloud features are 45 Km (about 28 miles) in diameter. Also this image shows the discovery of shadows in Neptune's Atmosphere, shadows cast onto a deep cloud bank by small elevated clouds. Located at about 68° South Lat., they are the first cloud shadows ever seen by the Voyager on any Planet.
The dark regions adjacent to the small bright clouds are believed to be shadows, because they are on the side of the cloud that is opposite to the incoming Sunlight and also because they lengthen in places where the Sun lies closer to the horizon".MareKromium
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ZA-Triton-PIA02247_modest.jpgFarewell Triton...69 visiteCaption NASA originale:"Voyager 2 obtained this parting shot of Triton, Neptune's largest satellite, shortly after closest approach to the moon and passage through its shadow on the morning of Aug. 25, 1989. The distance to Triton was 90.000 Km and the phase angle was 155°, so that only a thin crescent of Triton's south polar region can be seen. Because of the high phase angle, and perhaps because of scattering sunlight in Triton's hazy atmosphere, few surface features are also easily discernible". Un piccolo commento: non sembra anche a Voi di intuire una sottile somiglianza fra Tritone e Titano?...
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