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| Ariel |
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Ariel is a moon of Uranus discovered on 24 October 1851 by William Lassell. It was discovered at the same time as Umbriel.The first and so far only close-up observations of Ariel were made by the Voyager 2 probe during its 1986 Uranus fly-by. Voyager 2 made its closest approach of Ariel on January 24, 1986 and passed within 127 000 km of the moon. Because the moon's south pole was pointed towards the Sun, only the southern hemisphere was photographed.
Ariel's composition is roughly 70% ices (water ice, carbon dioxide ice, and possibly methane ices) and 30% silicate rock, and it appears to have regions of fresh frost in places, particularly in the ejecta radiating from young impact craters. The oldest and most extensive geologic unit observed on Ariel by Voyager 2 was a vast area of cratered plains centered near Ariel's south pole. Analysis of craters seen on Ariel's cratered plains suggest most are younger than many of those seen on Titania, Oberon, and Umbriel.[4] The largest crater observed on Ariel is Yangoor, at only 78 km across, and shows signs of deformation since its formation. Voyager 2 also observed a network of faults, canyons, and icy outflows running along Ariel's mid-southern latitudes, breaking up the cratered plains region. The canyons probably represent grabens formed by extensional faulting. Smooth material and grooves are often seen running down length of Ariel's valley networks, suggested that some canyon floors have been covered in warm ice extruded from Ariel's interior.
Ariel's past geologic activity is believed to have been driven by tidal heating at a time when its orbit was more eccentric than currently. Early in its history, Ariel was apparently captured in a 4:1 orbital resonance with Titania, from which it subsequently escaped. The resonance would have increased orbital eccentricity; resulting tidal friction due to time-varying tidal forces from Uranus would have caused warming of the moon's interior. In the Uranus system, due to the planet's lesser degree of oblateness, and the larger relative size of its satellites, escape from a mean motion resonance is much easier than for satellites of Jupiter or Saturn.
Ariel may be like Saturn's Dione. They are very similar in size, density and mass with Ariel only having slightly higher numbers. Both appear to have had past geological activity.
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| Miranda |
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Miranda
is the smallest and innermost of Uranus' five
major moons.It was discovered by
Gerard Kuiper on 1948-02-16 at McDonald
Observatory. It was named after Miranda from
William Shakespeare's play The Tempest by
Kuiper in his report of the discovery.
The adjectival form of the name is Mirandan.
It is also designated Uranus V.
So far the only close-up images of Miranda
are from the Voyager 2 probe, which made
observations of the moon during its Uranus flyby
in January, 1986. During the flyby the southern
hemisphere of the moon was pointed towards the
Sun so only that part was studied. It is
geologically the most active body in the Uranian
system.
Miranda's surface may be
mostly water ice, with the low density body also
likely containing silicate rock and organic
compounds in its interior.
Miranda's surface has patchwork regions of
broken terrain indicating intense geological
activity in the moon's past, and is criss-crossed
by huge canyons. Large 'racetrack'-like grooved
structures, called coronae, may have formed via
extensional processes at the tops of diapirs, or
upwellings of warm ice. The ridges probably
represent extensional tilt blocks. The canyons
probably represent grabens formed by extensional
faulting. Other features may be due to
cryovolcanic eruptions of icy magma. The diapirs
may have changed the density distribution within
the moon, which could have caused Miranda to
reorient itself, similar to a process believed
to have occurred at Saturn's geologically active
moon Enceladus. Miranda is one of the few bodies
in the solar system in which the equatorial
circumference is shorter than the pole-to-pole
circumference, likely a consequence of the
diapir activity.
Miranda's past geological activity is
believed to have been driven by tidal heating at
a time when its orbit was more eccentric than
currently. Early in its history, Miranda was
apparently captured in a 3:1 orbital resonance
with Umbriel, from which it subsequently
escaped. The
resonance would have increased orbital
eccentricity; resulting tidal friction due to
time-varying tidal forces from Uranus would have
caused warming of the moon's interior. In the
Uranus system, due to the planet's lesser degree
of oblateness, and the larger relative size of
its satellites, escape from a mean motion
resonance is much easier than for satellites of
Jupiter or Saturn. Miranda's orbital inclination
(4.34°) is unusually high for a body so close to
the planet. Miranda probably escaped from its
resonance with Umbriel via a secondary
resonance, and the mechanism of this escape is
believed to explain why its orbital inclination
is more than 10 times those of the other large
Uranian moons (see Uranus' natural satellites).
An earlier theory, proposed shortly after the
Voyager 2 flyby and now out of favor, was
that a previous incarnation of Miranda was
shattered by a massive impact, with the
fragments reassembling into the current strange
pattern.
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| Oberon |
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Oberon
is the outermost of the major moons of the
planet Uranus. With a mean radius of about 760
km., Oberon is the second largest moon of
Uranus, as well as the tenth largest moon in the
solar system.
It was discovered on January 11, 1787 by William
Herschel, in the same year that he reported
Titania. He would later report four more
satellites, which would turn out to be spurious.
Remarkably, for nearly fifty years
following their discovery, Titania and Oberon
would not be observed by any other instrument
than William Herschel's. However, the moon can
be seen from Earth with a present-day amateur
telescope.
So far the only close-up images of Oberon are
from the Voyager 2 probe, which
photographed the moon during its Uranus flyby in
January, 1986. At the time of the flyby the
southern hemisphere of the moon was pointed
towards the Sun, so the northern hemisphere
could not be studied.
Although its interior make-up is uncertain, one
model suggests that Oberon is composed of
roughly 50% water ice, 30% silicate rock, and
20% methane-related carbon/nitrogen compounds.
It has an old, heavily cratered, and icy surface
which shows little evidence of internal activity
other than some unknown dark material that
apparently covers the floors of many craters.
However, some large faults can be seen across
the southern hemisphere, which indicates some
internal activity early in its life.
So far, scientists have recognised a few types
of geological features on Oberon: craters,
chasmata, and mountains. In fact one such
mountain rises about 6 kilometers (3.7 miles)
above the Oberonian surface.
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Titania |
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Titania
is the largest moon of Uranus and the eighth
largest moon in the Solar System.
So far the only close-up images of Titania are
from the Voyager 2 probe, which
photographed the moon during its Uranus flyby in
January, 1986. At the time of the flyby the
southern hemisphere of the moon was pointed
towards the Sun; the northern hemisphere was
unobservable.
Although its interior composition is uncertain,
one model suggests that Titania is composed of
roughly 50% water ice, 30% silicate rock, and
20% methane-related organic compounds. A major
surface feature is a huge canyon that dwarfs the
scale of the Grand Canyon on Earth and is in the
same class as the Valles Marineris on Mars or
Ithaca Chasma on Saturn's moon Tethys.
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