| Piú viste - Neptune and His Moons |
Nereid-vg2_1138148.jpgNereid (HR)54 visitenessun commento
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Triton-PIA00329.jpgViews of Triton (natural colors - elab. NASA)54 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-PIA09927.jpgThe "Hot" South Pole of Neptune54 visiteCaption NASA:"These thermal images show a "hot" South Pole on the Planet Neptune. These warmer temperatures provide an avenue for Methane to escape out of the deep atmosphere.
The images were obtained with the Very Large Telescope in Chile, using an imager/spectrometer for mid-infrared wavelengths on Sept. 1 and 2, 2006.
The telescope is operated by the European Organization for Astronomical Research in the Southern Hemisphere (known as ESO).
Scientists say Neptune's South Pole is "hotter" than anywhere else on the Planet by about 10° Celsius (50 degrees Fahrenheit). The average temperature on Neptune is about -200° Celsius (-392 degrees Fahrenheit).
The upper left image samples temperatures near the top of Neptune's troposphere (near 100 millibar pressure, which is 1/10th the Earth atmospheric pressure at sea level). The hottest temperatures are indicated at the lower part of the image, at Neptune's south pole (see the graphic at the upper right).
The lower two images, taken 6.3 hours apart, sample temperatures at higher altitudes in Neptune's stratosphere. They do show generally warmer temperatures near, but not at, the south pole. They also show a distinct warm area which can be seen in the lower left image and rotated completely around the back of the planet and returned to the earth-facing hemisphere in the lower right image".MareKromium
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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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Triton.JPGNorthern Latitudes on Triton54 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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Triton_Mosaic.JPGTriton (photo-mosaic - credits: NASA)54 visiteCaption NASA:"This picture of Triton is a mosaic of the highest resolution images taken by Voyager 2 on Aug. 25, 1989 from a distance of about 40.000 Km (approx. 24.800 miles). The mosaic is superimposed on the lower resolution mapping images taken about 2 hours earlier in order to fill in gaps between high resolution images. The smallest features that can be seen on the images are about 0,8 Km (approx. 0,5 miles) across.
The Terminator (such as the line separating the day from the night) is at the top of the picture and is centered at about 30° North Lat. and 330° East Longitude.
These highest resolution images were targeted for the Terminator Region to show details of the topography by the shadows it casts. Near the center of the picture is a depression filled with smooth plains that are probably ices which were once erupted in a fluid state. The depth of the depression is about 300 meters (900 feet) and the prominent fresh impact crater on its floor is about 20 Km (approx. 12 miles) in diameter and about 1 Km (such as approx. 0,6 mile) deep. On the right is an elongate crater with adjacent dark deposits above it. This feature may be an explosive eruption vent formed by gaps within the ice.
The linear structure on the left is probably a fracture along which fresh ice has been extruded".MareKromium
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Z-Thalassa.gifThalassa53 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-vg2_1138639.jpgTriton (HR)53 visitenessun commento
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Triton-vg2_p34665.jpgTriton (in natural colors and HR)53 visitenessun commento
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