The five major Uranian satellites (left to right in mosaic: Miranda, Ariel, Umbriel,
Titania, and Oberon). Tiny Miranda is only 470 kilometers across.
Miranda and Ariel are the two smallest and innermost of the five major Uranian satellites.
Despite their small size (470 and 1160 kilometers across, respectively), they are
also the most complex geologically. Although the exact mechanism remains uncertain,
proximity to Uranus probably generated enough tidal heating to partially
melt some of these satellites and trigger volcanism and tectonic deformation
in the distant past.
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This six-frame mosaic of tiny Miranda is one of the best views of a satellite
obtained by Voyager during its amazing journey through the outer solar system.
Features as small as 300 meters across can be seen. Miranda is only 450
kilometers across, yet its surface is scarred by 10-kilometer-high fault
scarps, unusual dark craters, and concentric areas of fracturing and
volcanic resurfacing (termed coronae). These zones of resurfacing are now thought
to be a result of internal heating and melting of low-temperature
ices such as ammonia-water ice. These materials rose upward as blobs or diapirs,
fracturing the crust and triggering local volcanism. This view is shown at roughly
900 meters resolution due to its large size.
Ariel, 1160 kilometers across, is even more highly disrupted and resurfaced than
Miranda. Enormous canyons 3 to 5 kilometers deep can be seen near the
equator (top and right in this view). Smooth and ridged plains are signs of
viscous (or sticky) volcanic extrusions. Impact craters are seen but they are
not as common as on other Uranian satellites. The causes of this geologic
activity are unclear but may be related to the tidal heating process responsible
for volcanism on Io and Triton.
All images by Paul M. Schenk, Lunar and Planetary Institute, Houston, TX.
©Lunar and Planetary Institute, 1997
Supplemental Reading Materials
Beatty J. K., O'Leary B., and Chaikin A., eds. (1990) The New Solar System. Sky Publishing Corporation, Cambridge, Massachusetts; Cambridge University Press, New York. 326 pp.
Moons and Rings (1991) Voyage Through the Universe series. Time-Life Books, Alexandria, Virginia. 144 pp.
Rothery D. (1992) Satellites of the Outer Planets. Clarendon Press, Oxford. 208 pp.
Bergstralh J. et al., eds. (1991) Uranus. University of Arizona Press, Tucson. 1076 pp.
Schenk P. (1991) Fluid volcanism on Miranda and Ariel. Journal of Geophysical Research, 96, 1887-1906.
Pappalardo R. T. et al. (1997) Extensional tilt blocks on Miranda: Evidence for an upwelling origin of Arden Corona. Journal of Geophysical Research, 102, 13369.