Compositional maps of Saturn's moon Phoebe from imaging spectroscopy

Abstract

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 formed. By contrast, Saturn's regular satellites (with prograde, low-inclination, circular orbits) probably accreted within the sub-nebula in which Saturn itself formed. 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.

Constraints from Comets on the Formation and Volatile Acquisition of the Planets and Satellites

“…CO 2 is frequently seen on the surface of outer planet moons, but many possibilities exist for in situ production of this molecule. It has been observed on the surface of Saturn's satellites Phoebe (Clark et al 2005), Iapetus (Buratti et al 2005) and Hyperion (Cruikshank et al 2007) as well the Uranian moons Ariel, Umbriel and Titania (Grundy et al 2006). As with Jupiter's icy moons, it is currently unclear if this CO 2 is primordial or produced through surface chemistry or endogenic processes so no conclusion can be made about the formation processes of these satellites based on this measurement.…”

“…The well-studied variation δ 18 O of VSMOW as a function of global terrestrial glaciation, rainfall, and evaporation is a good example of this (e.g. Clark and Fritz 1997). The interaction between different stable isotopes in the formation of different types of oxygen bearing compounds produces a general trend that can be broken down by δ 18 O and δ 17 O values ( Fig.…”

Outer irregular satellites of the planets and their relationship with asteroids, comets and Kuiper Belt objects

“…Phoebe's density was found to be 1630 ± 33 kg m −3 (Porco et al 2005). The spectra showed lots of water ice as well as ferrous-iron-bearing minerals, bound water, trapped CO 2 , phyllosilicates, organics, nitriles and cyanide compounds on the surface (Clark et al 2005). Phoebe's volatile rich surface and many compounds infer the object was formed beyond the rocky main belt of asteroids and maybe very similar to the composition of comets.…”

Spectrodirectional remote sensing: From pixels to processes

“…4)-a good indication of the increasing relevance of this emerging topic. The table is based on searches performed in altavista.com, citations in scopus.com using combinations of keywords (e.g., hyperspectral, imaging spectroscopy, imaging spectrometry, directional, multiangular, spectrodirectional, and variants thereof), as of September 2004. A thematic separation of these search terms in the above overview will be increasingly difficult in the future, since methodologies used in Earth observation related imaging spectroscopy are now also widely used in deep space research (Clark et al, 2005), neurosciences (Devonshire et al, 2004), chemometrics (Fernández Pierna et al, 2004), amongst others.…”