| Risultati della ricerca nelle immagini - "Umbriel" |
UMBRIEL-PIA00040-PCF-LXTT-IPF.jpgUmbriel (Absolute Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga/Lunar Explorer Italia/Italian Planetary Foundation)75 visiteThe Southern Hemisphere of the Uranian moon Umbriel displays heavy Cratering in this NASA - Voyager 2 image, taken on January 24, 1986, at a distance of approx. 557.000 Km (such as a little less than 346.000 miles) from the Surface of the moon. This frame, taken through the Clear-Filter of Voyager's Narrow-Angle Camera, is the most detailed image of Umbriel that we have, with a resolution of about 10 Km (such as 6,21 miles) per picture element.
Umbriel is the darkest of Uranus' larger moons and the one that appears to have experienced the lowest level of Geological Activity. It has a diameter of about 1200 Km (a little more than 745 miles) and its Surface reflects only 16% of the light that receives; in the latter respect, Umbriel is similar to the Lunar Highland Areas of our own Moon. Umbriel, as we wrote herebefore, is heavily cratered, but it lacks the numerous Bright-Ray Craters that are commonly seen on the other large Uranian Natural Satellites; this fact, among other things, results in a relatively uniform Surface Albedo (---> Reflectivity).
The prominent Impact Crater visible on the Terminator (at about 11 o'clock of Umbriel's disk) is approx. 110 Km (such as 68,3 miles) across and it shows a really bright Central Peak. On the other hand, the strangest Surface Feature visible in this image (on the Limb of Umbriel, right at 12 o'clock of the disk) is a curious-looking Bright Ring which represents the most reflective area seen on Umbriel itself. The Bright Ring is about 140 Km (approx. 87 miles) in diameter and it lies near the moon's Equator. The nature of the Bright Ring is unknown, although it might be a very large Frost Deposit, perhaps associated with (located on top and near) the Rim of a huge Impact Cater. The few white spots that can be barely seen against the black background are not stars, but just just image artifacts, due to 'noise' in the data received on Earth.
This frame (which is the Original NASA - Voyager 2 b/w image published on the NASA - Planetary Photojournal with the ID n. PIA 00040) has been additionally processed and then colorized, according to an educated guess carried out by Dr Paolo C. Fienga (LXTT-IPF), in Absolute Natural Colors (such as the colors that a human eye would actually perceive if someone were onboard the NASA - Voyager 2 Spacecraft and then looked outside, towards the Neptunian moon Triton), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team. Different colors, as well as different shades of the same color, mean, among others, the existence of different Elements present on the Surface of Triton, each having a different Albedo (---> Reflectivity) and Chemical Composition.MareKromium
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UMBRIEL-vg2-SV.jpgUmbriel's most prominent Surface Features: Skynd and Wunda Craters (Natural Colors; credits: NASA)57 visiteThe surface of Umbriel is an ancient one.
A collection of impact craters of various sizes was found to saturate the landscape. As Voyager 2 drew closer, became clear that most or all of the bright features are related to craters. On the Terminator, one can see 2 interesting craters.
One, Skynd, has a bright Central Peak. The other, Wunda, at the top of the image, has a bright rim and no apparent Central Peak. This is the best color image obtained by Voyager 2.MareKromium
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UMBRIEL-vg2_p29502-A.jpgUmbriel's extremely unusual surface feature (HR - context image)66 visiteIl rilievo (che definire "fortemente anomalo" è riduttivo) che caratterizza il versante prossimo al Polo Nord di Umbriel è, almeno dalle immagini che sono in nostro possesso, del tutto inesplicabile.
Alcuni Ricercatori (anche nel Gruppo Lunar Explorer Italia) ipotizzano che si tratti di una montagna dalle dimensioni davvero incredibili (almeno in rapporto al corpo celeste a cui essa accede - immaginate come il Monte Everest apparirebbe dallo spazio se fosse alto 70 o più Km e largo 300, tanto per rendere l'idea...), mentre altri Studiosi ritengono che quello che si vede in questa immagine è solo il risultato di una deformazione del frame la quale potrebbe essere imputabile ad un vizio di trasmissione e/o di ricevimento ed elaborazione dati (il che equivarrebbe a dire che il rilievo in questione non esiste).
Altri ancora interpretano questo rilievo come una "plume" vulcanica (?) o una gigantesca formazione nuvolosa.
Purtroppo, il mistero non sarà risolto tanto facilmente...
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UMBRIEL-vg2_p29502-B.jpgUmbriel's extremely unusual surface feature: Wunda Crater (HR - detail mgnf)60 visitenessun commento
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UMBRIEL-vg2_p29502-Wunda.jpgUmbriel's extremely unusual surface feature: Wunda Crater (Natural Colors; credits: NASA)57 visiteHere is a closeup systhesis from all the close-ups of Wunda Crater.
It is hard to tell if the craters dug up the bright material, or if they had something to do with the impacts. Maybe it was derived from eruptions or melting caused by impacts.
Or maybe they are some sort of frost left over from impacts.
This issue may not be resolved until another spacecraft observes Umbriel. Here is the best view of Wunda that can be generated with the available data.MareKromium
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UMBRIEL.jpgFarewell Umbriel! (Natural Colors; credits: Ted Stryk)58 visitenessun commentoMareKromium
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Uranus-familyportrait-PIA01975_modest.jpgThe 5 major moons of Uranus63 visiteThis "family portrait" of Uranus' 5 largest moons was compiled from images sent back Jan. 20, 1986, by Voyager 2 spacecraft. The pictures were taken through a clear filter from distances of 5 to 6,1 MKM (3,1 to 3.8 MMs). In this comparison, we see the relative sizes and relativities of the satellites. From left, in order of increasing distance from the planet, they are Miranda, Ariel, Umbriel, Titania and Oberon. The 2 largest, Oberon and Titania, are about half the size of Earth's Moon, or roughly, 1.600 Km (1.000 miles) in diameter. Miranda, smallest of the 5, has about one-quarter to one-third the diameter. Even in these distant views, the satellites exhibit distinct differences in appearance. On average, Oberon and Titania reflect about 20% of the sunlight, Umbriel about 12%, Ariel and Miranda about 30%. Ariel shows the largest contrast on its surface, with the brightest areas about 25%. All five satellites show only slight color variations on their surfaces, with their average color being very nearly gray. The best views of the satellites will be obtained Jan. 24, the day of closest approach.
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