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Pluto and Charon: The "Double Planet"
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A - Pluto and Charon - HST.jpgPluto and Charon from the Hubble Space Telescope128 visiteAggiornamento del 19 Agosto 2006: il Sistema "Plutone-Caronte", sino a ieri considerato un sistema equiparabile a quello Terra-Luna (in cui Plutone, al pari della Terra, il Corpo Maggiore e Caronte, invece ed al pari della Luna, quello minore e dunque SOLO Satellite del primo), in accordo ad una decisione dell'International Astronomical Union (IAO) stato ora rubricato come "Doppio Pianeta".
Caption IAU originale:"Both Pluto and Charon each are large enough (massive enough) to be spherical. Both bodies independently satisfy the definition of planet. The reason they are called a double planet is that their common centre of gravity is a point that is located in free space outside the surface of Pluto. Because both conditions are met: each body is planet-like and each body orbits around a point in free space that is not inside one of them, the system qualifies to be called a Double Planet.
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B-Caron.jpgThe Discovey of Charon54 visiteCharon was discovered in June 1978 by U.S. Naval Observatory astronomers James Christy and Robert Harrington. They weren't even looking for satellites of Pluto - they were trying to refine Pluto's orbit around the Sun!
Charon was discovered when sharp-eyed Christy noticed the images of Pluto were strangely elongated - it looked like Pluto had an irregular blob attached to its side. Perhaps the telescope was joggled when the picture was taken? No, that possibility was quickly eliminated by noticing that the other stars on the photo were round. Moreover, the blob itself seemed to move around Pluto - the direction of elongation cycled back and forth over 6.39 days - Pluto's rotation period. From this, Christy, after being checked by Harrington, concluded that Pluto either possessed a mountain thousands of kilometers high or a satellite that orbited in its synchronous orbit.
Searching through their archives of Pluto images taken years before, Christy found more cases where Pluto appeared strangely elongated. Working independently, Christy measured the angle (from north) where the elongations appeared while Harrington calculated what the answer "should be" if the elongation was caused by an orbiting satellite. When the anxious moment came for them to compare their answers, they found perfect agreement. Just to be sure, they waited for the U. S. Naval Observatory 60-inch telescope to make one more confirmation. And sure enough, on July 2 new images showed the elongation due to a satellite right where it was supposed to be. They announced their discovery to the world on July 7, 1978. Christy proposed the name "Charon", after the mythological ferryman who carried souls across the river Acheron, one of the five mythical rivers that surrounded Pluto's underworld. Apart from the mythological connection for this name, Christy chose it because the first four letters also matched the name of his wife, Charlene.
Charon's satellite status was finally confirmed when Pluto and Charon began a series of mutual eclipses in 1985. Later, Hubble Space Telescope and even advanced ground-based telescopes were able to spot Charon orbiting nearby just 1/4000th of a degree from Pluto!MareKromium
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C-Pluto_Charon.jpgPluto and Charon, from the Subaru Telescope53 visiteThe excellent quality of its 8,3-meter primary mirror and the stability of the atmosphere above Mauna Kea, Hawaii, allowed the Subaru Telescope to provide clearly separated images of Pluto and Charon using its Cooled Infrared Spectrograph/Camera.
This image is produced from three 2-second exposures taken through infrared filters on June 9, 1999.
MareKromium
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PLUTO&CHARON.jpgPluto & Charon (1) from the Hubble Space Telescope128 visitePluto Statistics: discovered by Clyde W. Tombaugh on February, 18, 1930.
Mass (Kg): 1.27e+22
Mass (if Earth = 1): 2,125e-03
Equatorial radius (Km): 1,137
Equatorial radius (if Earth = 1): 0,1783
Mean density (gm/cm^3): 2,05
Mean distance from the Sun (Km): 5.913.520.000
Mean distance from the Sun (if Earth = 1): 39,5294
Rotational period (in days): 6,3872
Orbital period (in years): 248,54
Mean orbital velocity (Km/sec): 4,74
Orbital eccentricity: 0,2482
Tilt of axis (in degrees): 122,52
Orbital inclination (in degrees): 17,148
Equatorial surface gravity (in mt/sec^2): 0,4
Equatorial escape velocity (in Km/sec):1,2
Visual geometric albedo: 0,3
Magnitude (Vo): 15,12
Atmospheric composition: Methane and Nitrogen
Una delle poche immagini in nostro possesso che rappresentano il Sistema (Binario) Plutone-Caronte.
Posto ad una distanza pari a circa 40 volte la distanza Terra/Sole, Plutone (un mondo gelido - si pensa che la temperatura media al suolo sia intorno ai - 233 C - ed eternamente immerso nella notte) si trova ai confini del Sistema Solare, a ridosso della cd "Fascia di Kuiper".
Per lo studio di questo affascinante Sistema e per "spiare" ci che si trova oltre i suoi confini, stata progettata la Sonda "New Horizons" la quale dovrebbe partire nel 2006 e raggiungerlo nel Luglio 2015, se tutto andr bene.
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PLUTO&CHARON2.jpgPluto & Charon (2) from the European Southern Obs.125 visiteLa Sonda, a quel punto, "sfiorer" Plutone (passandogli a circa 9600 Km di distanza) e Caronte (transito previsto a circa 27.000 Km), prima di dirigersi (e perdersi...) nella Fascia di Kuiper, alla ricerca sia di oggetti oscuri - che, con non grandissima fantasia, sono stati chiamati "KBO", ovvero Kuiper's Belt Objects (o anche "TNO", e cio Trans Neptunian Objects) -, sia di risposte a tutti quei quesiti che ogni Scienziato, ogni volta che guarda il Cielo, non pu non porsi.
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PLUTO.jpgPluto in "true color"219 visiteOvviamente non sappiamo molto di Plutone, ma le pi recenti scoperte parlano di vasti depositi di acqua ghiacciata sulla sua superficie. Sappiamo pure che Plutone possiede un'atmosfera (composta da azoto, metano ed altri gas in misura minore) oltremodo sottile la quale, inevitabilmente, "ghiaccia" all'afelio del Pianeta (afelio--->il punto pi lontano dal Sole).
Il lancio della Sonda New Horizons stato concepito secondo tempistiche le quali dovrebbero portarla a ridosso di Plutone prima che la sua atmosfera ghiacci totalmente e quindi permetterci di studiarla (un minimo) ed analizzarne le componenti.
Facts-bites about Pluto&Charon:
Pluto orbits the Sun once every 248 years.
A person on Pluto would weigh 1/15 what they weigh on Earth - for comparison, the astronauts on the Moon had 1/6 of their Earth weight.
Pluto is named after the Greek god of the underworld.
The symbol for Pluto ("PL") is tribute to Percival Lowell, who started the search for the ninth planet in the early 1900s.
Charon is 20 times closer to Pluto than our moon is to Earth.
Pluto was discovered in 1930 by American astronomer Clyde Tombaugh.
American astronomers James Christy and Robert Harrington discovered Charon in 1978.
Charon is named after the mythological boatman who ferried souls across the river Styx to Pluto for judgment.
At 1,470 miles (about 2,370 kilometers) across, Pluto could fit between Washington, D.C. and Denver, Colorado.
Charon is half of Pluto's diameter - making it the largest satellite relative to the planet it orbits.
Pluto is an ice dwarf - a "new" type of planet common to the deep outer solar system.
Pluto-Charon is the solar system's only known binary planet.
Pluto's surface is among the most contrasty in the solar system.
Pluto has weather, winds, hazes, chemistry and an ionosphere.
Pluto's estimated surface temperature falls between --378 to --396 degrees F (-228 to -238 C).
Pluto is one of only two planets that rotates on its side - Uranus is the other.
Pluto's surface has nitrogen, methane and carbon monoxide ices on it.
A radio signal moving at the speed of light takes about 4 hours to reach Pluto from Earth.
The Kuiper Belt is a collection of icy, rocky objects residing beyond Neptune's orbit.
The first Kuiper Belt Object was discovered in 1992.
Some Kuiper Belt Objects (like Pluto) have an average reddish color, while others are gray.
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Pluto-421596main_s1006ay-1.jpgSurface Color-Variations on Pluto54 visiteSince its discovery in 1930, Pluto has been a speck of light in the largest ground-based telescopes. But NASA's Hubble Space Telescope has now mapped the Dwarf Planet in never-before-seen detail. The new map is so good, astronomers have even been able to detect changes on the Dwarf Planet's Surface by comparing Hubble images taken in 1994 with the newer images taken in 2002-2003. The task is as challenging as trying to see the markings on a soccer ball 40 miles away.
Hubble's view isn't sharp enough to see craters or mountains, if they exist on the surface, but Hubble reveals a complex-looking and variegated world with white, dark-orange, and charcoal-black terrain. The overall color is believed to be a result of UltraViolet radiation from the distant Sun breaking up Methane that is present on Pluto's Surface, leaving behind a dark, molasses-colored, carbon-rich residue.
Astronomers were very surprised to see that Pluto's brightness has changed the Northern Pole is brighter and the Southern Hemisphere is darker and redder. Summer is approaching Pluto's North Pole, and this may cause surface ices to melt and refreeze in the colder shadowed portion of the Planet. The Hubble pictures underscore that Pluto is not simply a ball of ice and rock but a dynamic world that undergoes dramatic atmospheric changes.MareKromium
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Pluto-421596main_s1006ay-2.jpgSurface Color-Variations on Pluto53 visiteNASA today released the most detailed set of images ever taken of the distant dwarf planet Pluto. The images taken by NASA's Hubble Space Telescope show an icy and dark molasses-colored, mottled world that is undergoing seasonal changes in its surface color and brightness. Pluto has become significantly redder, while its illuminated Northern Hemisphere is getting brighter. These changes are most likely consequences of surface ices sublimating on the sunlit Pole and then refreezing on the other Pole as the dwarf planet heads into the next phase of its 248-year-long seasonal cycle. The dramatic change in color apparently took place in a two-year period, from 2000 to 2002.
The Hubble images will remain our sharpest view of Pluto until NASA's New Horizons probe is within 6 months of its Pluto flyby. The Hubble pictures are proving invaluable for picking out the planet's most interesting-looking hemisphere for the New Horizons spacecraft to swoop over when it flies by Pluto in 2015.
Though Pluto is arguably one of the public's favorite planetary objects, it is also the hardest of which to get a detailed portrait because the world is small and very far away. Hubble resolves surface variations a few hundred miles across, which are too coarse for understanding Surface Geology. But in terms of surface color and brightness Hubble reveals a complex-looking and variegated world with white, dark-orange, and charcoal-black terrain. The overall color is believed to be a result of UltraViolet radiation from the distant Sun breaking up Methane that is present on Pluto's Surface, leaving behind a dark and red carbon-rich residue.
When Hubble pictures taken in 1994 are compared with a new set of images taken in 2002 to 2003, astronomers see evidence that the northern polar region has gotten brighter, while the southern hemisphere has gotten darker. These changes hint at very complex processes affecting the visible surface, and the new data will be used in continued research.
The images are allowing planetary astronomers to better interpret more than three decades of Pluto observations from other telescopes, says principal investigator Marc Buie of the Southwest Research Institute in Boulder, Colo. "The Hubble observations are the key to tying together these other diverse constraints on Pluto and showing how it all makes sense by providing a context based on weather and seasonal changes, which opens other new lines of investigation."
The Hubble pictures underscore that Pluto is not simply a ball of ice and rock but a dynamic world that undergoes dramatic atmospheric changes. These are driven by seasonal changes that are as much propelled by the Planet's 248-year elliptical orbit as its axial tilt, unlike Earth where the tilt alone drives seasons. The seasons are very asymmetric because of Pluto's elliptical orbit. Spring transitions to Polar Summer quickly in the Northern Hemisphere because Pluto is moving faster along its orbit when it is closer to the Sun.
Ground-based observations, taken in 1988 and 2002, show that the mass of the atmosphere doubled over that time. This may be due to warming and sublimating Nitrogen ice. The new Hubble images from 2002 to 2003 are giving astronomers essential clues about how the seasons on Pluto work and about the fate of its atmosphere.
The images, taken by the Advanced Camera for Surveys, are invaluable to planning the details of the New Horizons flyby in 2015. New Horizons will pass by Pluto so quickly that only one hemisphere will be photographed in the highest possible detail. Particularly noticeable in the Hubble image is a bright spot that has been independently noted to be unusually rich in carbon monoxide frost. It is a prime target for New Horizons. "Everybody is puzzled by this feature," says Buie. New Horizons will get an excellent look at the boundary between this bright feature and a nearby region covered in pitch-black surface material.
"The Hubble images will also help New Horizons scientists better calculate the exposure time for each Pluto snapshot, which is important for taking the most detailed pictures possible," says Buie. With no chance for re-exposures, accurate models for the surface of Pluto are essential in preventing pictures that are either under- or overexposed.
The Hubble images are a few pixels wide. But through a technique called dithering, multiple, slightly offset pictures can be combined through computer-image processing to synthesize a higher-resolution view than could be seen in a single exposure. "This has taken four years and 20 computers operating continuously and simultaneously to accomplish," says Buie, who developed special algorithms to sharpen the Hubble data.
The Hubble research results appear in the March 2010 issue of the Astronomical Journal. Buie's science team members are William Grundy of Lowell Observatory in Flagstaff, Ariz., and Eliot Young, Leslie Young, and Alan Stern of Southwest Research Institute in Boulder, Colo.
Buie plans to use Hubble's new Wide Field Camera 3 to make further Pluto observations prior to the arrival of New Horizons.MareKromium
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Pluto.jpgPluto & Charon (Ground View + HST View)111 visiteA dire il vero, il rischio maggiore per New Horizons (pi dei rischi di un viaggio di quasi 6 miliardi di Km) che i fondi necessari al suo lancio non vengano raccolti in tempo per soddisfare la citata "finestra di lancio". Inoltre, ad essere onesti, siamo rimasti molto sorpresi dai tempi stimati per il raggiungimento di Giove (poco pi di un anno) e quindi di Plutone.
Nuovi sistemi di propulsione, finestra di lancio (ultra) ottimale - con possibilit di effettuare qualche "swing" attorno ad altri Pianeti durante il viaggio e dunque accelerare), nostro errore di valutazione o informazioni eccessivamente ottimistiche?
Vedremo!...
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ZA-Pluto-NOT.jpgPluto & Charon106 visiteUn esempio di eccellente immagine del Sistema (Binario) costituito da Plutone e Caronte ottenuta direttamente dalla Terra. Certo, non possibile cogliere dettagli della superficie di Plutone (n, tantomeno, di Caronte), ma la risoluzione dei due dischi ci pare davvero buona. Plutone un mondo estremamente lontano e non ha mai costituito un obbiettivo di primario interesse, almeno sino a qualche tempo fa.
Tuttavia, alcune recenti scoperte relative, fra l'altro, alle peculiari caratteristiche della sua orbita, al tipo di relazione - in termini di rotazione - che intercorre fra Plutone stesso e Caronte e, infine, a delle (per ora inspiegabili) variazioni della sua albedo, hanno tutte contribuito ad accendere l'interesse degli Scienziati per questo mondo lontano che, forse, un giorno (fra qualche miliardo di anni, quando il Sole sar una Gigante Rossa e se l'Umanit - ma ne dubitiamo... - esister ancora) potrebbe anche diventare la nostra "casa".
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ZB-Surface map of Pluto-HST-PIA00826_modest.jpgA "Map" of Pluto, from HST84 visiteCaption NASA originale:"This map that covers about 85% of the surface of the Planet confirms that Pluto has a dark equatorial belt and bright polar caps. The brightness variations in this map may be due to topographic features such as basins and fresh impact craters. Pluto itself probably shows even more contrast and perhaps sharper boundaries between light and dark areas than is shown here, but HST resolution (just like early telescopic views of Mars) tends to blur edges and blend together small features sitting inside larger ones".
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ZB-T-Surface map of Pluto.jpgSurface Map of Pluto72 visiteQuando si parla del Sistema Plutone-Caronte in molti (anche noi...) parlano - a nostro avviso impropriamente - di "Sistema Binario", con ci intendendo il fatto che i due corpi celesti in questione hanno dimensioni similari e si muovono ad una modesta (sempre in termini cosmici) distanza media l'uno dall'altro. In realt il rapporto che lega Plutone a Caronte comunque un rapporto di "maggiore" a "minore" o, se preferite, di "Parent Planet" a "moon" (o "satellite") e quindi parlare di Sistema Binario errato.
Per Sistema Binario, infatti, si dovrebbe intendere un rapporto "alla pari" fra i 2 corpi il quale - prescindendo anche dalle loro effettive dimensioni - si fonda su un principio di "Equilibrio Gravitazionale" fra di essi. Un "equilibrio" in virt del quale non c' n un Parent Planet, n una moon, bens 2 corpi celesti "connessi ma indipendenti", i quali si muovono armonicamente e sincronicamente l'uno rispetto all'altro secondo traiettorie definite dalle loro reciproche interazioni gravitazionali.
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