| Piú viste - Neptune and His Moons |
NEPTUNE-Springtime.jpgSpring on Neptune from the Hubble Space Telescope88 visiteUna meravigliosa visione dell'Emisfero Sud di Nettuno e delle immense formazioni nuvolose bianche che sembrano essere la causa del suo notevole (e recente) aumento di luminosità.
L'Estate, anche per questo mondo lontano, si sta dunque avvicinando!
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NEPTUNE4.jpgNeptune from Voyager 285 visiteLe fotografie che Vi offriamo di Nettuno sono state, tranne forse un paio, tutte scattate dalla Sonda Voyager 2 che, come sapete, transitò molto vicina al Pianeta ed al suo Sistema di Lune nel 1989.
L'atmosfera di Nettuno è costituita, in prevalenza, da Idrogeno ed Elio (gas entrambi invisibili) e quindi gli Scienziati ritengono che il bel colorito azzurro del Pianeta sia determinato dalla presenza di sensibili quantitativi di Metano atmosferico (un gas che assorbe, preferenzialmente, le radiazioni...
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Neptune-bw-PIA02222.jpgNeptune and the "Great Dark Spot"84 visiteCaption NASA originale:"This photo was taken by Voyager 2's wide-angle camera. Light at methane wavelengths is mostly absorbed in the deeper atmosphere. The bright, white feature is a high-altitude cloud just south of the Great Dark Spot. Other, smaller clouds associated with the Great Dark Spot are white, and are also at high altitudes.
The Voyager Mission was conducted by JPL for NASA's Office of Space Science and Applications".
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NEPTUNE.jpgNeptune from Voyager 282 visiteL'anno di Nettuno, a livello di curiosità, dura circa 165 anni terrestri e, quindi, ognuna delle sue "stagioni" si estende per oltre 41 anni.
Adesso è ancora Primavera su Nettuno, ma l'Estate è alle porte (inizierà, nell'Emisfero Sud, nel 2005).
Può sembrare un fatto incredibile (basti pensare che la luce solare, su Nettuno, è circa 900 volte meno intensa di quanto essa lo sia sulla Terra) eppure, all'avvicinarsi dell'Estate, il clima di Nettuno sembra "rispondere" di conseguenza. E' stato infatti notato, mettendo a confronto immagini del Pianeta riprese dall'HST nel 1996 rispetto ad altre riprese (sempre dell'HST) nel 2002, un notevole incremento della sua luminosità superficiale causata dall'aumento di nuvole bianche presenti, appunto, nell'Emisfero Sud, cioè quello per cui l'Estate si sta rapidamente approssimando.
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AA-Neptune-HST-PIA01287_modest.jpgNeptune from HST82 visiteLa seconda serie di immagini del Pianeta Nettuno, ripreso dal Telescopio Spaziale Hubble. Poco da aggiungere rispetto a quanto già detto in precedenza se non che la (quasi totale) impossibilità di fotografare amatorialmente Nettuno dalle nostre latitudini dipende da un continuo e costante degrado dell'atmosfera che ci circonda: inquinamento gassoso ed inquinamento luminoso fanno a gara per vedere quale dei due sia il peggiore.
Purtroppo, sebbene per motivi ed in ambiti diversi, sono entrambi "letali"!
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Neptune-PIA01982.jpgClouds near the "Eye" of Neptune (Natural Colors; credits: Lunexit)82 visiteCaption NASA:"The bright cirrus-like clouds of Neptune change rapidly, often forming and dissipating over periods of several to tens of hours. In this sequence, Voyager 2 observed cloud evolution in the region around the Great Dark Spot (GDS).
The surprisingly rapid changes which occur separating each panel shows that in this Region Neptune's weather is perhaps as dynamic and variable as that of the Earth. However, the scale is immense by our standards -- the Earth and the GDS are of similar size -- and in Neptune's frigid Atmosphere, where temperatures are as low as 55 degrees Kelvin (-360 F), the cirrus clouds are composed of frozen Methane rather than Earth's crystals of water ice".MareKromium
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TRITON2.jpgTriton from Voyager 2 (enhanced real colors)78 visiteUn dettaglio della superficie di Tritone, sempre ripresa dal Voyager 2 (da notare che le gradazioni di colore e, conseguentemente, la qualità del dettaglio e dei particolari, sono state artificiosamente accentuate/i).
Una curiosità: a quanto è stato possibile accertare sino ad ora, le caratteristiche morfologiche superficiali di Tritone sembrano davvero molto simili a quelle di Plutone. Due mondi simili (due KBOs?) con un comune passato remoto e che, magari, sono destinati ad un comune lontano futuro...
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Triton-PIA00317-PCF-LXTT-IPF.jpgThe Southern Regions of Triton (Absolute Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga/Lunar Explorer Italia/Italian Planetary Foundation)77 visiteThis wonderful and highly detailed global Absolute Natural Color image mosaic of Triton was obtained in the AD 1989 by the NASA - Voyager 2 Spacecraft during its Fly-By of the Neptunian System.
With a radius of approx. 1350 Km (such as a little more than 838 miles) and therefore some 22% smaller than Earth's Moon, Triton is by far the largest Natural Satellite of Neptune. Furthermore, Triton is one of the only 3 (three) objects in the Solar System known to have a Nitrogen-dominated Atmosphere (the others are our Home Planet Earth and the Saturnian giant moon, Titan). Triton has the coldest Surface known anywhere in the Solar System (38 K, or about - 391 degrees Fahrenheit, or - 235° Celsius): it is so cold that most of Triton's Nitrogen is condensed as Frost, making it the only Celestial Body in the whole Solar System that is known to have a Surface mainly composed of Nitrogen Ice.
The pinkish deposits constitute a vast South Polar Cap, that is believed to contain Methane Ice, which somehow reacted under Sunlight so 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 Fly-By. The light gray colored band visible in this image extends all the way around Triton, near the Equator and it may consist of relatively fresh Nitrogen Frost Deposits. The vaguely greenish areas of Triton (central and upper right side) include what is known as "The Cantaloupe Terrain", whose origin is still unknown, and a set of "Cryovolcanic" Landscapes apparently produced by Icy-cold Liquids (now totally frozen) that were erupted from Triton's interior.
This frame (which is the Original NASA - Voyager 2 color image mosaic published on the NASA - Planetary Photojournal with the ID n. PIA 00317) has been additionally processed and then re-colorized, according to an educated guess carried out by Dr Paolo C. Fienga (LXTT-IPF), in Absolute Natural Colors (such as the colors that a human eye would actually perceive if someone were onboard the NASA - Voyager 2 Spacecraft and then looked outside, towards the Neptunian moon Triton), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team. Different colors, as well as different shades of the same color, mean, among others, the existence of different Elements present on the Surface of Triton, each having a different Albedo (---> Reflectivity) and Chemical Composition.MareKromium
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Triton-PIA02246-PCF-LXTT-IPF.jpgStill in the Abyss (Absolute Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunar Explorer Italia/Italian Planetary Foundation)77 visiteFeatures as small as approx. 100 Km (such as a little more than 62 miles) across can be seen in this Absolut Color Image of Neptune's moon Triton, photographed by the NASA - Voyager 2 Spacecraft on August 20, 1989, while it was still approx. 5,4 Million KiloMeters (such as about 3,35 Million Miles) from Neptune. Triton's overall light pinkish color may be due to the heavy irradiation (---> the action of the Cosmic Rays and other Charged Particles, including the ones forming the Solar Wind) of the Ice (and, maybe, other Elements which were already) existing on the Surface of this distant Celestial Body.
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. However - and generally speaking -, the darker areas visible on Triton appear to be somewhat redder in color than the brighter ones. The central Longitude in the image is 123° East. The South Pole of Triton is at about 6 o'clock of the disk, approximately 1/6th (one sixth) of the way up from its lower limb.
This frame (which is the Original NASA - Voyager 2 color frame published on the NASA - Planetary Photojournal with the ID n. PIA 02246) has been additionally processed and then re-colorized, according to an educated guess carried out by Dr Paolo C. Fienga (LXTT-IPF), in Absolute Natural Colors (such as the colors that a human eye would actually perceive if someone were onboard the NASA - Voyager 2 Spacecraft and then looked outside, towards the Neptunian moon Triton), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team. Different colors, as well as different shades of the same color, mean, among others, the existence of different Elements present on the Surface of Triton, each having a different Albedo (---> Reflectivity) and Chemical Composition.MareKromium
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Neptune-HST1.JPGViews of Neptune (from Hubble Space Telescope)76 visitenessun commentoMareKromium
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PROTEUS.jpgProteus75 visiteUna luna minore del Sistema di Nettuno: Proteus.
Caratterizzata da una forma solo vagamente sferica, questa luna presenta un gigantesco - e facilmente visibile - cratere da impatto in prossimità del suo Polo Nord (fotografico).
Forse è proprio questo cratere la "cicatrice" generata dall'urto che ha spinto "Proteus" al di fuori dalla Fascia di Kuiper e poi verso Nettuno, dalla cui gravità è stato infine catturato.
Un probabilissimo KBO, dunque, o - come dicono alcuni - un Trans Neptunian Object.
O forse una cometa mancata.
Forse.
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Triton-clouds-PIA02203.jpgClouds on the limb of Triton75 visiteCaption NASA originale:"Limb clouds over Triton's South Polar Cap. Image is stretched to enhance the limb clouds and surface features. The image shows the cloud on the west limb that extends about 100 Km along the limb and appears detached over much of its length".
Nuvole nel cielo di Tritone: non si tratta di un'ipotesi affascinante, bensì di un fatto. Ora la domanda non può che essere questa: qual'è la composizione delle nuvole di Tritone?
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