Editor's Summary

5 May 2005

Phoebe a Kuiper-belt refugee?

Phoebe, the outermost large satellite of Saturn, is of particular interest because its unusual orbit suggests that it was gravitationally captured by Saturn, having formed outside the solar nebula where Saturn itself formed. The Cassini−Huygens spacecraft encountered Phoebe on 11 June 2004, and imaging spectroscopy from Cassini was used to detect iron, bound water, trapped CO₂, phyllosilicates, organics, nitriles and cyanide compounds on Phoebe. The presence of all these compounds makes Phoebe one of the most compositionally diverse objects in our Solar System, consistent with a surface of cometary origin incorporating primitive materials from the outer Solar System. Further evidence on Phoebe's past comes from density measurements made by two other instrument systems on Cassini. Phoebe's composition is distinctly different from the ice-rich material that formed the intermediate-sized saturnian satellites, and is consistent with formation from the same material out of which Pluto and Triton (archetypical Kuiper-belt objects) formed.

News and Views: Planetary science:  Saturn's retrograde renegade

Data from the Cassini−Huygens mission provide convincing evidence that the saturnian moon Phoebe formed elsewhere in the Solar System, and was only later captured by Saturn's gravitational pull.

J. Brad Dalton

doi: 10.1038/435033a

Full Text | PDF (134K)

Letter: Compositional maps of Saturn's moon Phoebe from imaging spectroscopy

Roger N. Clark, Robert H. Brown, Ralf Jaumann, Dale P. Cruikshank, Robert M. Nelson, Bonnie J. Buratti, Thomas B. McCord, J. Lunine, K. H. Baines, G. Bellucci, J.-P. Bibring, F. Capaccioni, P. Cerroni, A. Coradini, V. Formisano, Y. Langevin, D. L. Matson, V. Mennella, P. D. Nicholson, B. Sicardy, C. Sotin, Todd M. Hoefen, John M. Curchin, Gary Hansen, Karl Hibbits and K.-D. Matz

doi: 10.1038/nature03558

First paragraph | Full Text | PDF (356K)

Letter: Saturn's moon Phoebe as a captured body from the outer Solar System

Torrence V. Johnson and Jonathan I. Lunine

doi: 10.1038/nature03384

First paragraph | Full Text | PDF (153K)