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Why might water freezing inside Miranda have fractured its surface?
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Uranus
Two views of the southern hemisphere of Uranus, produced from images obtained by Voyager 2 on Jan. 17, 1986. In colours visible to the unaided human eye, Uranus is a bland, nearly featureless sphere (left). In a colour-enhanced view processed to bring out low-contrast details, Uranus shows the banded cloud structure common to the four giant planets (right). From the polar perspective of Voyager at the time, the bands appear concentric around the planet's rotational axis, which is pointing nearly toward the Sun. Small ring-shaped features in the right image are artifacts arising from dust in the spacecraft's camera.
The fracturing of Miranda’s surface, characterized by its spectacular riftlike canyons, is believed to be the result of internal expansion.1
Scientists hypothesize that this expansion, estimated at approximately 6 percent of the moon's volume, occurred if the water within Miranda’s interior was once in a liquid state and subsequently froze after the moon's outer crust had already formed. Because water expands as it transitions into ice under low pressure, this internal freezing would have caused the moon's volume to increase, effectively stretching and shattering the surface crust.1