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Compositional maps of Saturn's moon Phoebe from imaging spectroscopy


The origin of Phoebe, which is the outermost large satellite of Saturn, is of particular interest because its inclined, retrograde orbit suggests that it was gravitationally captured by Saturn, having accreted outside the region of the solar nebula in which Saturn formed1. By contrast, Saturn's regular satellites (with prograde, low-inclination, circular orbits) probably accreted within the sub-nebula in which Saturn itself formed2. Here we report imaging spectroscopy of Phoebe resulting from the Cassini–Huygens spacecraft encounter on 11 June 2004. We mapped ferrous-iron-bearing minerals, bound water, trapped CO2, probable phyllosilicates, organics, nitriles and cyanide compounds. Detection of these compounds on Phoebe makes it one of the most compositionally diverse objects yet observed in our Solar System. It is likely that Phoebe's surface contains primitive materials from the outer Solar System, indicating a surface of cometary origin.

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Figure 1: VIMS data, x and y axes show longitude and latitude, respectively, in degrees.
Figure 2: Spectra of Phoebe show the presence of numerous compounds.


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This work was funded by the Cassini project. Authors from American institutions were funded by NASA; authors from European institutions were funded by ESA.

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Correspondence to Roger N. Clark.

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Clark, R., Brown, R., Jaumann, R. et al. Compositional maps of Saturn's moon Phoebe from imaging spectroscopy. Nature 435, 66–69 (2005).

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