| Piú viste - Neptune and His Moons |
NeptuneandTriton_vg2_big.jpgNeptune and Triton from Voyager 273 visiteNettuno possiede, così come Giove, Saturno ed Urano, un Sistema di lune estremamente complesso, dal quale spiccano Tritone (qui in foto accanto a Nettuno) e Nereide.
Si tratta, come testimoniano le immagini che possediamo, di corpi rocciosi sostanzialmente privi di atmosfera (anche se per Tritone quest'ultima asserzione sembra essere non veritiera) e pertanto soggetti - anche ai giorni nostri - ad un'elevata attività di bombardamento meteorico.
Le altre lune che fanno parte del Sistema di Nettuno (a parte Proteus, di cui possediamo qualche immagine) sono troppo piccole per essere esaminate nei particolari ma si presume che possa trattarsi di corpi (in origine) cometari o di altri corpi "erranti" sfuggiti, a seguito di impatti e/o di influenze mareali (o per altre cause a noi ignote), alla Fascia di Kuiper ed in seguito "catturati" dalla gravità del Pianeta.
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Neptune-PIA00048.jpgNeptune in true colors, from Voyager 270 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-StrechedNaturalColors.JPGNeptune and a few of His Moons (Voyager 2 - Natural, but enhanced, Colors; credits: NASA)69 visiteCaption NASA:"Voyager 2 was the first spacecraft to observe the planet Neptune and its two satellites: Triton, the largest, and Nereid.
The most obvious feature of the Planet is its blue color, the result of Methane in the Atmosphere. Research continues on Neptune's two largest satellites and the additional 6 that were discovered by Voyager 2's investigation". MareKromium
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Triton-PIA02214_modest.jpgTriton from Voyager 2 (false colors)67 visiteCaption NASA originale:"This false color image of Triton is a composite of images taken through the violet, green and ultraviolet filters. The image was taken early on Aug. 25, 1989 when Voyager 2 was about 190.000 Km (118.000 miles) from Triton's surface. The smallest visible features are about 4 Km(2,5 miles) across. The image shows a geologic boundary between completely dark materials and patchy light/dark materials. A layer of pinkish material stretches across the center of the image. The pinkish layer must be thin because underlying albedo patterns show through. Several features appear to be affected by the thin atmosphere; the elongated dark streaks may represent particulate materials blown in the same direction by prevailing winds and the white material may be frost deposits".
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AA-Neptune-CJH.jpgSmiling Neptune and soft, white, water-clouds - from Voyager 2 (HR)66 visiteUn'immagine davvero meravigliosa, ottenuta dalla Sonda Voyager 2, durante il suo rapido passaggio accanto all'ultimo Gigante Gassoso del nostro Sistema Solare. Era il 31 Agosto 1989...
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Neptune-South_Hem-V2-PIA00050_modest.jpgThe Southern Polar Region of Neptune from approx. 4.200.000 Km65 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 più veloci e violenti. Un sistema configurato in maniera interessante ma, probabilmente, piuttosto instabile.
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Neptune-newmoons-PIA01991.jpgNew moons of Neptune64 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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Neptune_sEye-TheDarkSpot-V2-CJH.gifThe "Dark Spot" of Neptune64 visitenessun commento
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ZA-Neptune_s Rings-PIA01997_modest.jpgThe Rings of Neptune (full system) 163 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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AA-Neptune-HST-PIA01284.jpgNeptune in "Primary Colors" - HST62 visiteCaption NASA originale:"These 2 NASA HST images provide views of weather on opposite hemispheres of Neptune. Taken Aug. 13, 1996, with Hubble's Wide Field Planetary Camera 2, these composite images blend information from different wavelengths to bring out features of Neptune's blustery weather. The predominant blue color of the planet is a result of the absorption of red and infrared light by Neptune's methane atmosphere. Clouds elevated above most of the methane absorption appear white, while the very highest clouds tend to be yellow-red as seen in the bright feature at the top of the right-hand image. Neptune's powerful equatorial jet - where winds blow at nearly 900 mph! - is centered on the dark blue belt just south of Neptune's equator. Farther south, the green belt indicates a region where the atmosphere absorbs blue light".
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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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Neptune-PIA02209_modest.jpgNeptune from 176.000.000 Km - Voyager 261 visiteCaption NASA originale:"These pictures of Neptune were obtained by Voyager 2 on April 26,1989, at a distance of 176 MKM. At the center of the Neptune disc, each pixel covers a square 4° by 4° in latitude. (Each Voyager image contains 800 pixels, picture elements, per line and 800 lines.) Resolution here was 3256 Km per line pair. The violet, clear and orange filters of Voyager's narrow-angle camera were used to produce the color pictures. Image processing enhances contrast of the features. The picture on the right was taken five hours after that at left, during which time the planet rotated 100°. The dark spot visible in the left picture appeared in clear filter images obtained three months earlier. A much brighter, white spot, prominent in the earlier images, has now apparently faded. The white spot near the south pole in the right picture is new. It was visible only faintly in a picture taken 18 hours earlier at the same longitude. This evidence of dynamic activity was unexpected in Neptune's atmosphere because Neptune receives only one-tenth of one percent as much solar energy as does the Earth".
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