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L

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RE: Phoebe Map
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This map is part of a group release of Mercator and polar stereographic projections of Saturn's moon Phoebe. A Mercator projection is a map that preserves directions on a body, but distorts sizes, especially near the poles.
This global digital map of Phoebe was created using data taken during the Cassini spacecraft's close flyby of the small moon in June 2004.


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The mosaic is projected into the Mercator projection within the latitude range of 57 degrees south to 57 degrees north latitude; the stereographic projections represent latitudes greater and lower than plus or minus 55 degrees.

The nomenclature was proposed by the Cassini imaging team and has yet to be validated by the International Astronomical Union. Resolution of the digital mosaic is 233 metres per pixel, although the highest resolution images have resolutions of 70 metres per pixel.

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L

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RE: Phoebe
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This global digital map of Saturn's moon Phoebe was created using data taken during the Cassini spacecraft's close flyby of the small moon in June 2004. The map is an equidistant projection and has a scale of 233 meters per pixel.


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The mean radius of Phoebe used for projection of this map is 107 kilometres. The resolution of the map is 8 pixels per degree.

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Scientists have concluded that Saturn's moon Phoebe originated in the outer solar system, and is similar to Pluto and other members of the Kuiper Belt.
"Cassini is showing us that Phoebe is quite different from Saturn's other icy satellites, not just in its orbit but in the relative proportions of rock and ice. It resembles Pluto in this regard much more than it does the other Saturnine satellites." - Dr. Jonathan Lunine, Cassini interdisciplinary scientist.


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Phoebe has a density consistent with that of the only Kuiper Belt objects for which densities are known. Phoebe’s mass, combined with an accurate volume estimate from images, yields a density of about 1.6 grams per cubic centimetre, much lighter than most rocks but heavier than pure ice, which is about 0.93 grams per cubic centimetre. This suggests a composition of ice and rock similar to that of Pluto and Neptune's moon Triton.
Whether the dark material on other moons of Saturn is the same primordial material as on Phoebe remains to be seen.

"Phoebe was left behind from the solar nebula, the cloud of interstellar gas and dust from which the planets formed. It did not form at Saturn. It was captured by Saturn's gravitational field and has been waiting eons for Cassini to come along." - Dr. Torrence Johnson, Cassini imaging team member.


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Saturn's pock-marked moon Phoebe could be a comet that was captured by the gravity of the ringed planet.
Data from the Cassini spacecraft during a close flyby on 11 June 2004, suggests it originated in the frozen outer Solar System region called the Kuiper Belt - a reservoir for comets.

The tiny satellite is very different in its chemical composition to Saturn's larger moons and circles the planet in the opposite direction to them.

"When we finally understand Phoebe, we will also understand the Kuiper Belt objects" - Ralf Jaumann, German Aerospace Centre
"It could have been a comet. Phoebe has a long journey behind it. It comes from the outer Solar System and probably rounded the Sun a few times before it was captured by Saturn's orbit. But we really don't know." - Ralf Jaumann of the German Aerospace Centre (DLR).

Phoebe and the objects that populate the Kuiper Belt are remnants of primordial objects that served as the building blocks of planets in our Solar System.
The saturnine satellite could itself be between 4 and 4.4 billion years old.
During the formation of the planets, gravitational interactions ejected some so-called icy planetesimals like Phoebe into distant orbits to join a native population of similar cosmic bodies.
This process formed the region we know today as the Kuiper Belt.
Phoebe itself must have migrated inwards and was captured by Saturn's gravity after the ringed planet formed from its planetary nebula.
Analysis of Phoebe's surface shows that it is one of the most complex Solar System objects yet studied.



Scientists have identified water-ice, possible clays, iron-bearing minerals and organics such as aromatic compounds, alkanes and nitriles on the 220km-wide saturnine satellite. More complex organics also seem to be there, but scientists are yet to characterise them.
The observations come from Cassini's Visual and Infrared Mapping Spectrometer (Vims).
Dr Jaumann thinks clays could have formed through heating if Phoebe came close to the Sun before being captured by Saturn, forcing water ice to react with silicates.
Phoebe's surface composition also suggests that chemical activity in the first half billion years of the Solar System may have been more complex than previously thought.



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