| Piú viste - Neptune and His Moons |
Triton-PIA02213_modest.jpgThe limb of Triton (natural colors - elab. NASA)64 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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Triton-PIA00061_modest.jpgTriton's Northern Hemisphere in HR64 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"64 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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Nereid-CJH.gifNereid64 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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Triton-PIA01994.jpgStrange "surface features" on Triton (clouds?!?)64 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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Triton-vg2_1138639.jpgTriton (HR)64 visitenessun commento
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Triton.JPGNorthern Latitudes on Triton64 visiteVoyager 2 took this picture of Neptune's largest satellite, Triton, from less than 80.000 Km (about 50.000 miles). The image shows an area in Triton's Northern Hemisphere.
The Sun is just above the horizon, so features cast shadows that accentuate height differences. The large, smooth area in the right-hand side of the image shows a single, fresh, impact crater. Otherwise there is no evidence of impacts such as those that have pocked the faces of most of the satellites Voyager 2 has visited.
Many low cliffs in the area, bright where they face the Sun, and when they face away from it, suggest and intricate history for Triton. The cliffs might be due either to melting of surface materials or, possibly, caused by unusual fluid materials that flowed sometime in Triton's past.MareKromium
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Neptune_and_Despina-transit_combo_despinabrightened.jpgNeptune and Despina64 visiteDalla Rubrica "NASA - Picture of the Day", del giorno 3 Settembre 2009:"Despina is a tiny moon of Neptune. A mere 148 Km across, diminutive Despina was discovered in 1989, in images from the Voyager 2 Spacecraft taken during its encounter with the Solar System's most distant Gas Giant Planet. But looking through the Voyager 2 data 20 years later, amateur image processor (and philosophy professor) Ted Stryk discovered something no one had recognized before -- images that show the shadow of Despina in transit across Neptune's blue cloud tops.
His composite view of Despina and its shadow is composed of four archival frames taken on August 24, 1989, separated by 9 minutes. Despina itself has been artificially brightened to make it easier to see.
In ancient Greek mythology, Despina is a daughter of Poseidon (the Roman god Neptune)".MareKromium
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Neptune-clouds-PIA01982_modest.jpgThe clouds of Neptune (b/w) - 263 visiteAncora i "cirri" di Nettuno, ripresi dalla Sonda Voyager 2, mentre si spostano rapidamente nei pressi - e lungo i bordi, in particolare- della Grande Macchia Scura (o GDS, come dicono alla NASA).
E' curioso pensare che i mutamenti del clima, su Nettuno, possano in qualche modo essere simili ai mutamenti di clima che possiamo riscontrare nel cielo della nostra Terra.
Già, ma in fondo - a pensarci bene - le nuvole ed il vento devono essere fenomeni assolutamente universali.
Certo, le nuvole di Nettuno non sono costituite da cristalli d'acqua, bensì da cristalli di metano ghiacciato ed i venti di Nettuno superano i 2000 Km orari. Ma le nuvole restano nuvole ed il vento - per quanto forte possa essere - rimane vento. Forse queste considerazioni sono banali, ma noi siamo convinti che, di tanto in tanto, sia una cosa giusta quella di pensare a quanto diversi, eppure quanto simili, possano essere i fenomeni della Natura qui, sulla Terra, o su Marte, o su Nettuno od ovunque - probabilmente - nell'Universo.
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Neptune-PIA02220.jpgSouth Polar Clouds and Shadows (Natural Colors; credits: Lunexit)63 visiteCaption NASA:"This image of Neptune shows the discovery of shadows in Neptune's Upper Atmosphere, shadows cast onto a deep cloud band by small elevated clouds. They are the first cloud shadows ever seen by Voyager 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".MareKromium
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Neptune-PIA02245.jpgNeptune from 16.000.000 Km60 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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Proteus2.jpgProteus (HR)60 visitenessun commento
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