Jupiter: the "King" and His Moons

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Inizio > SOLAR SYSTEM > Jupiter: the "King" and His Moons

AA-Jupiter-PIA02666_modest.jpgJupiter from Cassini-Huygens115 visiteJupiter Data and Statistics
Mass (kg) = 1.900e+27
Mass (Earth = 1) = 3,1794e+02
Equatorial radius = 71.492 Km
Equatorial radius (Earth = 1) = 1,1209e+01
Mean density (gm/cm^3) = 1,33
Mean distance from the Sun = 778.330.000 Km
Mean distance from the Sun (Earth = 1) = 5,2028
Rotational period (days) = 0,41354
Orbital period (days) = 4332,71
Mean orbital velocity = 13,07 Km per second
Tilt of axis = 3,13°
Orbital inclination = 1,308°
Equatorial surface gravity (m/sec^2) = 22,88
Equatorial escape velocity = 59,56 Km per second
Magnitude (Vo) = - 2,70
Mean cloud temperature = - 121°C
Atmospheric pressure (bars) = 0,7
Atmospheric composition: Hydrogen 90%; Helium 10%

Amalthea and Io-PIA01626.jpgAmalthea and Io (approx. true colors)131 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.

Amalthea-Galileo.jpgAmalthea, from Galileo53 visiteOn its way in and out, Galileo took these two snapshots of Amalthea. The purpose was to improve navigation for the upcoming flyby of this little moonlet, but such images also help in the study of the shape of irregular worlds.MareKromium

Amalthea-PIA01072.jpgFirst look at Amalthea61 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. (...) ".

Amalthea-PIA01074.jpgFour views of Amalthea69 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.

Amalthea-PIA01076.jpgAmalthea and a few inner Moons of Jupiter66 visiteChe cosa distingue questi "macigni vaganti" dalla maggior parte delle Lune di Giove? Si tratta di Lune originarie del Sistema Gioviano o sono state "attratte" da Giove, durante un passaggio troppo ravvicinato? Probabilmente si tratta di asteroidi vaganti o di comete mancate: oggetti provenienti dalla Fascia di Kuiper (KBO) che, in transito accanto al Gigante Gassoso, si sono trovati all'angolo ed alla velocità corretti per non essere nè semplicemente deflessi dalla loro corsa e quindi scagliati via nello...

Amalthea-PIA02532.jpgA white streak on Amalthea66 visite...spazio interstellare, nè per essere attratti ed ingurgitati definitivamente da Giove, come è invece accaduto alla Cometa Shoemaker-Levy. Molti Scienziati non escludono neppure l'ipotesi che possa trattarsi di frammenti di una Luna Gioviana disintegratasi (magari a seguito di una collisione) qualche milione di anni fa. La verità, come sempre, non sarà facile da trovarsi...

Amalthea-PIA07248_modest.jpgAmalthea: just an "Ice Cube"!55 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.

Callisto-040507.jpgCallistus, from New Horizons53 visiteThe New Horizons Long Range Reconnaissance Imager (LORRI) captured these two images of Jupiter's outermost large moon, Callisto, as the spacecraft flew past Jupiter in late February.
New Horizons' closest approach distance to Jupiter was 2,3 MKM (about 1,4 MMs), not far outside Callisto's orbit, which has a radius of 1,9 MKM (about 1,2 MMs). However, Callisto happened to be on the opposite side of Jupiter during the spacecraft's pass through the Jupiter System, so these images, taken from 4,7 MKM (about 3 MMs) and 4,2 MKM (about 2,6 MMs) away, are the closest of Callisto that New Horizons obtained.
Callisto's ancient, crater-scarred surface makes it very different from its three more active sibling satellites, Io, Europa and Ganymede. Callisto, 4800 Km (about 3000 miles) in diameter, displays no large-scale geological features other than impact craters and every bright spot in these images is a crater. The largest impact feature on Callisto, the huge basin Valhalla, is visible as a bright patch at the 10 o'clock position. The craters are bright because they have excavated material relatively rich in water ice from beneath the dark, dusty material that coats most of the surface.

The two images show essentially the same side of Callisto - the side that faces Jupiter - under different illumination conditions. The images accompanied scans of Callisto's infrared spectrum with New Horizons' Linear Etalon Imaging Spectral Array (LEISA).
The New Horizons Science Team designed these scans to study how the infrared spectrum of Callisto's water ice changes as lighting and viewing conditions change, and as the ice cools through Callisto's late afternoon.
The infrared spectrum of water ice depends slightly on its temperature, and a goal of New Horizons when it reaches the Pluto system (in 2015) is to use the water ice features in the spectrum of Pluto's moon Charon, and perhaps on Pluto itself, to measure surface temperature.
Callisto provided an ideal opportunity to test this technique on a much better-known body.

The left image, taken at 05:03 Universal Time on February 27, 2007, is centered at 5° South, 5° West, and has a Solar Phase Angle of 46°. The right image was taken at 03:25 Universal Time on February 28, 2007. It is centered at 4° South, 356° West, and has a Solar Phase Angle of 76°.MareKromium

Callisto-Asgard emi.-Gal-PIA00562_modest.jpgThe "Asgard" hemisphere of Callisto (detail mgnf)54 visiteCaption NASA originale:"...Dominating the scene is the impact structure, Asgard, centered on the smooth, bright region near the middle of the picture and surrounded by concentric rings up to 1.700 kilometers in diameter. A second ringed structure with a diameter of about 500 kilometers can be seen to the north of Asgard, partially obscured by the more recent, bright-rayed crater, Burr. The icy materials excavated by the younger craters contrast sharply with the darker and redder coatings on older surfaces of this Moon..."

Callisto-Asgard emisph.-Gal-PIA01100_modest.jpgThe "Asgard" hemisphere of Callisto53 visiteCaption NASA originale:"False color view of a portion of the leading hemisphere of Jupiter's moon Callisto as seen through the infrared filters of the Solid State Imaging (CCD) system aboard NASA's Galileo spacecraft. North is to the top of the picture and the sun illuminates the surface from the east. More recent impacts have excavated bright, relatively clean ice from beneath Callisto's battered surface. Callisto's dark mottled appearance may be due to contamination by non-ice components contributed by impactors or concentrated in a residue as ice is removed".

Callisto-Chain of craters-PIA00514_modest.jpgA chain of craters on Callisto94 visiteCaption NASA originale:"A portion of a chain of impact craters on Jupiter's moon Callisto is seen in this image taken by the Galileo spacecraft on November 4, 1996. This crater chain on Callisto is believed to result from the impact of a split object, similar to the fragments of Comet Shoemaker-Levy 9 which smashed into Jupiter's atmosphere in July of 1994".

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