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| Ultimi arrivi - Jupiter: the "King" and His Moons |
Amalthea and Io-PIA01626.jpgAmalthea and Io (approx. true colors)143 visiteComposite view of Amalthea and Io at the same scale. The visible part of Amalthea is about 150 Km across. The colors are just approximate. Amalthea is actually much darker than Io, but is displayed at a similar brightness for ease of viewing. The shape of Amalthea is controlled largely by impact cratering and fragmentation. In contrast, Io, like Earth, has gravity sufficient to form it into a slightly ellipsoidal sphere. Amalthea is covered by craters because there are no processes which erode or cover them efficiently. On extremely volcanically active Io, impact craters are covered quickly by lavas and other volcanic materials. Some of the volcanic materials escape from Io and probably contribute to the reddish colors of Amalthea and the other small inner satellites. The Amalthea and Io composites, obtained by the Solid State Imaging (SSI) camera on NASA's Galileo spacecraft on different orbits, were placed side by side for comparison purposes. The Amalthea composite combines data taken with the clear filter of the SSI system during orbit six, with lower resolution color images taken with the green, violet, and 1 micrometer filters during orbit 4. The Io data was obtained on July 2nd, 1998 (orbit 14) using the green, violet, and 1 micrometer filters.
Ott 20, 2005
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Jupiter_s Rings-PIA01627.jpgThe Rings of Jupiter (1)57 visiteOriginal caption:"This schematic cut-away view of the components of Jupiter's Ring System shows the geometry of the Rings in relation to Jupiter and to the small inner moons, which are the source of the dust forming the Rings themselves. The innermost and thickest Ring, shown in gray shading, is the halo that ends at the Main Ring. The thin, narrow Main Ring, shown with red shading, is bounded by the 16- Km-wide (10-miles) satellite Adrastea and shows a marked decrease in brightness near the orbit of Jupiter's innermost moon, Metis. It is composed of fine particles knocked off Adrastea and Metis. Although the orbits of Adrastea and Metis are about 1000 Km (about 600 miles) apart, that separation is not depicted in this drawing. Impacts by small meteoroids (fragments of asteroids and comets) into these small, low-gravity satellites feed material into the Rings. Thebe and Amalthea, the next 2 moons in increasing distance from Jupiter, supply dust which forms the thicker, disk-like 'Gossamer' Rings". Ott 17, 2005
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Jupiter_s Rings-PIA01628.jpgThe Rings of Jupiter (2)57 visiteScientists studying data from Galileo spacecraft have found that the Ring System is made up of impact debris created when meteoroids, which are fragments of comets and asteroids, slam into Jupiter`s four smallest satellites. The top panel shows that the Main Ring (red) is formed mostly from meteoroid impact debris kicked up from the innermost moons, Metis (m) and Adrastea (a). Since both satellites orbit in paths not inclined to Jupiter's equator, the Main Ring appears as a narrow line. The middle panel shows the additional effect of dust ejected from the satellite Amalthea (A), responsible for producing 1 of the 2 moon components of the Gossamer Ring. Amalthea's orbit is inclined to Jupiter's equatorial plane and at different times the satellite's vertical position can range anywhere between the 2 extreme limits shown. Dust ejected from Amalthea (orange) produces a ring whose thickness equals Amalthea's vertical projections beyond Jupiter's equatorial plane. The lower panel shows the additional effect of dust ejected from Thebe (T), which makes up the second component (shown in green) of the gossamer ring. Again, the two positions shown represent the maximum projections of Thebe from Jupiter's equatorial plane. This component of the gossamer ring is thicker than the component due to Amaltheas dust because Thebe's orbit is more inclined than that of Amalthea.
Ott 17, 2005
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Amalthea-PIA01072.jpgFirst look at Amalthea69 visiteOriginal caption:"Galileo's first view of Amalthea, a small inner moon of Jupiter, showing the end of the elongated satellite that faces permanently toward the Giant Planet. North is to the top of the picture and the Sun illuminates the surface from the left. The circular feature that dominates the upper-right portion of the disk is Pan, the largest crater on Amalthea. This crater is about 90 Km wide. The bright spot at the South Pole is associated with another, slightly smaller crater named Gaea. (...) ".Ott 17, 2005
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Amalthea-PIA01074.jpgFour views of Amalthea75 visiteThese 4 images of Amalthea were taken by Galileo's Solid State Imaging System at various times between February and June 1997. North is approx. up in all cases. Amalthea, whose longest dimension is about 247 Km (154 miles) across, is tidally locked (like Thebe) so that the same side of the moon always points towards Jupiter. In such a tidally locked state, one side of Amalthea always points in the direction in which Amalthea moves as it orbits about Jupiter. This is called the "leading side" of the moon and is shown in the top 2 images. The opposite side of Amalthea, such as the "trailing side," is shown in the bottom pair of images. The Sun illuminates the surface from the left in the top left image and from the right in the bottom left image. Such lighting geometries, similar to taking a picture from a high altitude at sunrise or sunset, are excellent for viewing the topography of the satellite's surface such as impact craters and hills. In the two images on the right, however, the Sun is almost directly behind the spacecraft. This latter geometry, similar to taking a picture from a high altitude at noon, washes out topographic features and emphasizes Amalthea's albedo (light/dark) patterns. It emphasizes the presence of surface materials that are intrinsically brighter or darker than their surroundings. The bright albedo spot that dominates the top right image is located inside a large south polar crater named Gaea.Ott 17, 2005
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Ganymede-PIA02582.jpgScarps on Ganymede56 visiteOriginal caption:"NASA's Galileo spacecraft took this image of dark terrain within Nicholson Regio, near the border with Harpagia Sulcus on Jupiter's moon Ganymede. The ancient, heavily cratered dark terrain is faulted by a series of scarps. The faulted blocks form a series of "stair-steps" like a tilted stack of books. On Earth, similar types of features form when tectonic faulting breaks the crust and the intervening blocks are pulled apart and rotate. This image supports the notion that the boundary between bright and dark terrain is created by that type of extensional faulting.
North is to the right of the picture and the Sun illuminates the surface from the west (top). The image is centered at -14° latitude and 320° longitude and covers an area approx. 16 by 15 Km (about 10 by 9 miles). The resolution is 20 mt (66 feet) per picture element. The image was taken on May 20, 2000, at a range of 2.090 Km (about 1.299 miles)".Ott 17, 2005
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Ganymede-PIA02580.jpgCalderas on Ganymede?64 visiteThe shallow, scalloped depression in the center of this picture from NASA's Galileo spacecraft is a caldera-like feature 5 to 20 Km (3 to 12 miles) wide on Jupiter's largest moon, Ganymede.
Calderas are surface depressions formed by collapse above a subsurface concentration of molten material. Some shallow depressions in bright, smooth areas of Ganymede have some overall similarities to calderas on Earth and on Jupiter's moon Io. On Ganymede, caldera-like depressions may serve as sources of bright, volcanic flows of liquid water and slush - an idea supported by a Ganymede photo obtained by Galileo during its seventh orbit (PIA01614). In the more recent image here, from Galileo's 28th orbit, a tall scarp marks the western boundary of a caldera-like feature. The western scarp is aligned similarly to older tectonic grooves visible in the image, suggesting the feature has collapsed along older lines of weakness. The interior is mottled in appearance, yet smooth compared to most of Ganymede's bright terrain seen at high resolution. The eastern boundary of the caldera-like feature is cut by younger, grooved terrain. Small impact craters pepper the scene, but the lack of a raised rim argues against an impact origin for the caldera-like feature itself. Instead, water-rich icy lava may have once flowed out of it toward the east. If so, later tectonism could have erased any telltale evidence of volcanic flow fronts. Direct evidence for icy volcanism on Ganymede continues to be elusive.
North is to the top of the picture and the Sun illuminates the surface from the left. The image, centered at -24 degrees latitude and 318degrees longitude, covers an area approximately 162 by 119 kilometers(101 by 74 miles). The resolution is 43 meters (141 feet) per picture element.
Ott 17, 2005
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Ganymede and Europa-PIA02574.jpgGanymede and Europa: so different and yet so similar!60 visiteThis frame compares a HR view of Arbela Sulcus on Ganymede (top) with the gray band Thynia Linea on another Jovian moon, Europa (bottom), shown to the same scale. Both images are from NASA's Galileo spacecraft.
Arbela Sulcus is one of the smoothest lanes of bright terrain identified on Ganymede, but subtle striations are apparent here along its length. This section of Arbela contrasts markedly from highly fractured terrain to its west and dark terrain to its east.
On Europa, gray bands such as Thynia Linea have formed by tectonic crustal spreading and renewal. Such bands have sliced through and completely separated pre-existing features in the surrounding bright, ridged plains. The younger prominent double ridge Delphi Flexus cuts across Thynia Linea. The scarcity of craters on Europa attests to the relative youth of its surface compared to Ganymede's.
Unusual for Ganymede, it is possible that Arbela Sulcus has formed by complete separation of Ganymede's icy crust, like bands on Europa. Tests of this idea come from detailed comparisons of their internal shapes and the relationships to the surrounding structures.
In the Ganymede image, north is to the top of the picture and the Sun illuminates the surface from the west. The image, centered at -15degrees latitude and 347 degrees longitude, covers an area approximately 34 by 26 kilometers (21 by 16 miles). The resolution is 34 meters (112 feet) per picture element. The image was taken on May 20, 2000, at a range of 3,370 kilometers (2,094 miles).
In the Europa image, north is to the upper-right of the picture and the Sun illuminates the surface from the northwest. The image, centered at-66 degrees latitude and 161 degrees longitude, covers an area approximately 44 by 46 kilometers (27 by 29 miles). The resolution is 45 meters (147 feet) per picture element. The image was taken on September 26, 1998, at a range of 3,817 kilometers (2,371 miles).
Ott 17, 2005
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Thebe-PIA01075.jpgThebe59 visiteOriginal caption:"These 2 images of the Jovian moon Thebe were taken by Galileo's solid state imaging system in November 1996 and June 1997, respectively. North is approximately up in both cases. Thebe, whose longest dimension is about 116 Km (or 72 miles) across, is tidally locked so that the same side of the satellite always points towards Jupiter, similar to how the nearside of our own Moon always points toward Earth. In such a tidally locked state, one side of Thebe always points in the direction in which Thebe moves as it orbits about Jupiter. This is called the "leading side" of the moon and is shown at the left. The image on the right emphasizes the side of Thebe that faces away from Jupiter (the so-called "anti-Jupiter" side). Note that there appear to be at least three or four very large impact craters on the satellite - very large in the sense that each of these craters is roughly comparable in size to the radius of Thebe".
Nota: crateri troppo grandi per un mondo così piccolo...Ott 17, 2005
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Jupiter-HR.jpgJupiter's North Pole (HR)59 visiteDa "NASA - Picture of the Day" dell'11-09-2005:"Gas giant Jupiter is the Solar System's largest world with about 320 times the mass of Earth. Famous for its Great Red Spot, Jupiter is also known for its regular, equatorial cloud bands, also visible in very modest sized telescopes.
The dark belts and light-colored zones of Jupiter's cloud bands are organized by the Planet's girdling winds which reach speeds of up to 500 Km/hour. On toward the Jovian poles though, the cloud structures become more mottled and convoluted until, as in this Cassini spacecraft mosaic of Jupiter, the Planet's Polar Region begins to look something like a brain. This striking equator-to-pole change in cloud patterns is not presently understood, but may be due in part to the effect of Jupiter's rapid rotation or to convection vortices generated at high latitudes by the massive Planet's internal heat loss.
Cassini took this dramatically detailed view of Jupiter in December 2000, during its flyby enroute to Saturn".Set 11, 2005
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Jupiter&Comet Shoemaker.jpgComet Shoemaker impacting Jupiter59 visiteQuesta spettacolare ripresa - ottenuta dall'HST - ci mostra alcuni dettagli relativi ai momenti successivi alla sequenza di impatti che, nel Luglio 1994, interessarono gli strati superiori dell'atmosfera di Giove.
Per quelli che non ricordano tutta la storia diciamo che queste immagini ci raccontano della fine (spettacolare, comunque) incontrata dai residui della cometa Shoemaker-Levy la quale, durante la sua corsa verso l'interno del Sistema Solare - ivi, lo Spazio di Giove -, venne "fatta a pezzi" (letteralmente) dalle onde gravitazionali provenienti dal Re dei Giganti Gassosi.Set 11, 2005
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Amalthea-PIA07248_modest.jpgAmalthea: just an "Ice Cube"!62 visiteThese images of Jupiter's moon Amalthea were taken with NASA's Galileo and Voyager spacecraft. Recent findings show that Amalthea is almost pure water ice, hinting that it may not have formed where it now orbits! This information challenges long-held theories about how moons form around giant planets. The image on the left shows the Escape Velocities (EV) color-coded on a shape model of Amalthea with the same viewpoint as the Voyager spacecraft image in the middle panel. Blue represents the lowest EV, barely 1 mt/second (about 3 feet) near the anti-Jupiter end, while red (barely visible) shows the region of much higher EV, nearly 90 mt/second (295 feet). The low EV result from the low density of Amalthea and from its rapid rotation as it orbits Jupiter.
The middle image is a composite from both Galileo and NASA's Voyager spacecraft and shows Amalthea from the anti-Jupiter side. The visible area is about 150 Km (about 93 miles) across.
The Sun is behind the spacecraft, resulting in loss of visible shadows. The brighter markings on the ends of a ridge are prominent in this view.
On the right is a Galileo image of Amalthea, (see PIA02532), with the bright spots on the end of Amalthea seen from the leading side of the satellite. Here the Sun is to the left and topography, such as the impact crater at the right, is visible.
Amalthea is Jupiter's fifth largest moon. It orbits about 181,000 kilometers (112,468 miles) from Jupiter, considerably closer than the Moon orbits Earth. It measures about 168 miles in length and half that in width. Galileo passed within about 99 miles of the moon on Nov. 5, 2002. After more than 30 close encounters with Jupiter's four largest moons, the Amalthea flyby was the last moon flyby for Galileo. The mission began orbiting the planet in 1995.
Ago 09, 2005
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