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NEPTUNE3.jpgNeptune from Voyager 294 visiteUn ciclopico ed ultrasecolare uragano anche per Nettuno, quindi?
Sembra di si, anche se delle risposte più accurate potranno venire solo da esami ed osservazioni, rispettivamente, maggiormente prolungati e ravvicinate.
Ci sono Missioni alle viste per Nettuno?
Purtroppo no, e allora dobbiamo rimetterci all'HST e dobbiamo altresì sperare che qualcuno alla NASA si ricordi di rendere note le informazioni e le scoperte riguardanti questo mondo azzurro e bianco, così bello e rassicurante - in apparenza - eppure così lontano, violento (da tanti punti di vista) e diverso dal nostro.
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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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NEPTUNE5.jpgNeptune from Voyager 2105 visite...luminose che agiscono sulla lunghezza d'onda del rosso).
Il movimento delle meravigliose formazioni nuvolose che caratterizzano gli strati superiori dell'atmosfera del Pianeta, come riprese dalla Sonda Voyager 2, ci hanno anche permesso di calcolare la velocità approssimativa dei venti che le muovono.
E così, a seguito di questo semplice calcolo, è stato possibile accertare che i venti di Nettuno sono i più forti dell'intero Sistema Solare: essi soffiano, infatti, a circa 2000 Km orari!
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NEPTUNE_S EYE.jpgNeptune from Voyager 2 - The "Blue Spot"95 visiteA questo proposito c'è pure chi sostiene che Plutone stesso, in un remoto passato, fosse un satellite di Nettuno e che, forse, tornerà ad esserlo - sia pure solo in un lontano futuro.
In questa foto: l'Occhio di Nettuno o, come dicono gli astronomi, la "Grande Macchia Blu" (The Big Blue Spot).
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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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Neptune-HST1.JPGViews of Neptune (from Hubble Space Telescope)76 visitenessun commentoMareKromium
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Neptune-HST2.JPGNeptune and a few of His Moons (HST; Natural Colors; credits: NASA)57 visitenessun commentoMareKromium
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Neptune-HST4.JPGMoments of Neptune (HST - False Colors; credits: NASA, L. Sromovsky and P. Fry - University of Wisconsin-Madison)54 visitenessun commentoMareKromium
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Neptune-June2011-HST.jpgOne Neptunian Day...89 visiteCaption NASA:"Neptune rotates once on its axis in about 16 hours. So, spaced about 4 hours apart these 4 images of the Solar System's most distant Gas Giant cover one Neptune day. Recorded by the Hubble Space Telescope in late June 2011, they combine exposures made with visible and Near-InfraRed filters to show high-altitude Clouds composed of Methane ice crystals against the Planet's normally blue Cloud Tops.
Because Neptune's axis of rotation is tilted to its orbital plane by 29°, compared to Earth's 23,5°, Neptune experiences seasons analogous to Earth's.
As early Summer comes to Neptune's Southern Hemisphere and Winter to the North, Hubble observations have shown Cloud activity shifting to the Northern Hemisphere. In fact the progression of Neptune's seasons has come around once since its position was predicted by French mathematician Urbain Le Verrier and British mathematician John Couch Adams, and the Planet was subsequently discovered by German astronomer Johann Galle on September 23, 1846. With an orbital period of approximately 165 years, this week on July 12, 2011, Neptune has been once around the Sun since its discovery date".MareKromium
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Neptune-PIA00048.jpgNeptune in true colors, from Voyager 269 visiteOriginal caption:"This image of clouds in Neptune's atmosphere is the first that tests the accuracy of the weather forecast that was made eight days earlier (nota: questa caption è relativa all'Estate del 1989) to select targets for the Voyager narrow angle camera. Three of the four targeted features are visible in this photograph; all 3 are close to their predicted locations.
The "Great Dark Spot" with its bright white companion is slightly to the left of center. The small bright "Scooter" is below and to the left, and the second "Dark Spot" with its bright core is below the Scooter. Strong eastward winds up to 400 mph cause the second dark spot to overtake and pass the larger one every five days. The spacecraft was 6,1 MKM (about 3,8 MMs) from the Planet at the time of camera shuttering, and the images uses the orange, green and clear filters of the camera".
Qualche nota sui Voyager 1 e 2: Voyager 1, launched September 5, 1977, visited Jupiter in 1979 and Saturn in 1980. It is now leaving the solar system, rising above the ecliptic plane at an angle of about 35 degrees, at a rate of about 520 million kilometers a year.
Voyager 2, launched August 20, 1977, visited Jupiter in 1979, Saturn in 1981 and Uranus in 1986 before making its closest approach to Neptune on August 25, 1989. Voyager 2 traveled 12 years at an average velocity of 19 kilometers a second (about 42,000 miles an hour) to reach Neptune, which is 30 times farther from the Sun than Earth is. Voyager observed Neptune almost continuously from June to October 1989. Now Voyager 2 is also headed out of the solar system, diving below the ecliptic plane at an angle of about 48 degrees and a rate of about 470 million kilometers a year.
Both spacecraft will continue to study ultraviolet sources among the stars, and their fields and particles detectors will continue to search for the boundary between the Sun's influence and interstellar space. If all goes well, we will be able to communicate with the two spacecraft for another 20 years, until their radioactive power sources can no longer supply enough electrical energy to power critical subsystems.
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Neptune-PIA01286_modest.jpgA new "dark spot" on Neptune, as seen by HST54 visiteCaption NASA originale:"NASA's HST has discovered a new Great Dark Spot, located in the Northern Hemisphere of Neptune. Because the planet's Northern Hemisphere is tilted away from Earth, the new feature appears near the limb of the planet.
The Spot is a near mirror-image to a similar Southern Hemisphere Dark Spot that was discovered in 1989 by the Voyager 2. In 1994, HST showed that the Southern Dark Spot had gone. Like its predecessor, the new Spot has high altitude clouds along its edge, caused by gasses that have been pushed to higher altitudes where they cool to form methane ice crystal clouds. The Dark Spot may be a zone of clear gas that is a window to a cloud deck lower in the atmosphere. Planetary scientists do not know how long this new feature might live. HST's HR images will allow astronomers to follow the spot's evolution and other unexpected changes in Neptune's dynamic atmosphere. This image was taken on 2.11-'94 with HST's Wide Field Planetary Camera 2, when Neptune was 4,5 BKMs from Earth".
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Neptune-PIA01539_modest.jpgFarewell Neptune: a "bright smile" for the Earthlings...61 visiteCaption NASA originale:"Voyager 2's post-encounter view of Neptune's South Pole as the spacecraft sped away on a southward trajectory".
E con la Sonda Voyager 2 che sfiorava Nettuno e poi si dirigeva verso i più estremi confini del Sistema Solare - perdendosi per sempre nello spazio interstellare - quest'ultimo frame ci mostra (passateci il termine) il "sorriso" di Nettuno per noi Terrestri.
Un "luminoso sorriso" che a noi piace pensare sia il suo modo di dire "Arrivederci"...
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