A common feature of Uranus seems to be the presence of poorly reflecting materials on all the solid bodies that surround it. In fact, even its major satellites are much darker than the moons of the other giant planets of the solar system: the moon with the lowest reflecting power is Umbriel (12%), followed by Oberon and Titania (20%) and by Ariel and Miranda (30%). Let's explore these new worlds one by one as they were revealed by Voyager. The most external satellite (586 000 kilometers from Uranus) is Oberon which, with a diameter of 1 600 kilometers, is also the largest in the Uranian system together with Titania. Its surface, which is rather flat and uniform, is furrowed with impact craters on its icy ground which can be distinguished from the surrounding territory thanks to their very dark bottom: this might be material with a high carbon content that flowed from the crust at the time of the collision and then solidified. Around the craters, light radial structures extend outward which are similar to those observed on Callisto, one of Jupiter's moons. Two particular structures were revealed in this landscape: a huge "mountain", with a height of about 6 000 meters which emerges from the edge of the satellite, and an enormous impact crater with a small central and lighter peak located in the center of the visible hemisphere. Titan, located inside the orbit of Oberon, is 438 000 kilometers from the surface of the planet. It was filmed by Voyager from a distance of 500 000 kilometers. In addition to numerous impact craters, these pictures also show many geologically interesting structures: a large jagged furrow and valleys with widths ranging from 50 to 100 kilometers and lengths of hundreds of kilometers which would provide evidence of the presence, in this icy satellite, of an interior that is still rather active. Umbriel, which is 267 000 kilometers from Uranus and has a diameter of 1 200 kilometers, is not only the darkest satellite, but also the one that has the least number of color variations. Due to the great distance from which Voyager filmed this moon (more than one million kilometers) and its poor reflectivity, its surface only reveals numerous impact craters and a strange light spot in the shape of a ring that stands out on the edge of its disk. The fourth satellite, Ariel, which orbits the planet at a distance of 192 000 and has a diameter of 1 300 kilometers, instead had the good fortune of being filmed at a distance of only 130 000 kilometers. Thus, it was possible to observe a greater variety of surface features. The oldest traces are undoubtedly the many impact craters, while the most recent structures are the long linear cracks which intersect over the entire surface and the windy overlapping furrows which are probably due to movements of fluid masses. But the most unusual object filmed by Voyager was certainly Miranda, the innermost satellite of Uranus, which is only 130 000 kilometers from the surface of the planet and the smallest of the larger satellites. In this case, Voyager flew by at only 31 000 kilometers and, thanks to a special rotation of the television cameras, it was possible to reconstruct an almost complete mosaic of the satellite, in which there are very small details with amazing clarity. Miranda thus was found to be the strangest hybrid of the entire solar system: the surface has a mix of craters and canyons, faults and alignments, projections and depressions which have already been observed at various times on other bodies, but never all together on only one. These structures probably were created during various geological periods in the history of the moon and are proof of very violent events: geologists literally jumped at the opportunity to analyze to discover once again a piece in the extraordinary never-ending puzzle offered by the space around us.
A common feature of Uranus seems to be the presence of poorly reflecting materials on all the solid bodies that surround it. In fact, even its major satellites are much darker than the moons of the other giant planets of the solar system: the moon with the lowest reflecting power is Umbriel (12%), followed by Oberon and Titania (20%) and by Ariel and Miranda (30%). Let's explore these new worlds one by one as they were revealed by Voyager. The most external satellite (586 000 kilometers from Uranus) is Oberon which, with a diameter of 1 600 kilometers, is also the largest in the Uranian system together with Titania. Its surface, which is rather flat and uniform, is furrowed with impact craters on its icy ground which can be distinguished from the surrounding territory thanks to their very dark bottom: this might be material with a high carbon content that flowed from the crust at the time of the collision and then solidified. Around the craters, light radial structures extend outward which are similar to those observed on Callisto, one of Jupiter's moons. Two particular structures were revealed in this landscape: a huge "mountain", with a height of about 6 000 meters which emerges from the edge of the satellite, and an enormous impact crater with a small central and lighter peak located in the center of the visible hemisphere. Titan, located inside the orbit of Oberon, is 438 000 kilometers from the surface of the planet. It was filmed by Voyager from a distance of 500 000 kilometers. In addition to numerous impact craters, these pictures also show many geologically interesting structures: a large jagged furrow and valleys with widths ranging from 50 to 100 kilometers and lengths of hundreds of kilometers which would provide evidence of the presence, in this icy satellite, of an interior that is still rather active. Umbriel, which is 267 000 kilometers from Uranus and has a diameter of 1 200 kilometers, is not only the darkest satellite, but also the one that has the least number of color variations. Due to the great distance from which Voyager filmed this moon (more than one million kilometers) and its poor reflectivity, its surface only reveals numerous impact craters and a strange light spot in the shape of a ring that stands out on the edge of its disk. The fourth satellite, Ariel, which orbits the planet at a distance of 192 000 and has a diameter of 1 300 kilometers, instead had the good fortune of being filmed at a distance of only 130 000 kilometers. Thus, it was possible to observe a greater variety of surface features. The oldest traces are undoubtedly the many impact craters, while the most recent structures are the long linear cracks which intersect over the entire surface and the windy overlapping furrows which are probably due to movements of fluid masses. But the most unusual object filmed by Voyager was certainly Miranda, the innermost satellite of Uranus, which is only 130 000 kilometers from the surface of the planet and the smallest of the larger satellites. In this case, Voyager flew by at only 31 000 kilometers and, thanks to a special rotation of the television cameras, it was possible to reconstruct an almost complete mosaic of the satellite, in which there are very small details with amazing clarity. Miranda thus was found to be the strangest hybrid of the entire solar system: the surface has a mix of craters and canyons, faults and alignments, projections and depressions which have already been observed at various times on other bodies, but never all together on only one. These structures probably were created during various geological periods in the history of the moon and are proof of very violent events: geologists literally jumped at the opportunity to analyze to discover once again a piece in the extraordinary never-ending puzzle offered by the space around us.
