Decoding the Domino: The Dark Side of Iapetus

Owen, Tobias; Cruikshank, D. P.; Ore, C. M. Dalle; Geballe, T. R.; Roush, T. L.; Bérgh, C. de; Meier, R.; Pendleton, Y. J.; Khare, B. N.

doi:10.1006/icar.2000.6521

Cited by 80 publications

(82 citation statements)

References 55 publications

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“…The CGS4 data were obtained in individual spectral segments of 0.15-0.64 µm that were also separated in time, while the SpeX data were obtained simultaneously over the region 0.8-2.5 µm in several orders of a cross-dispersed echelle. Our study of the low-albedo hemisphere of Iapetus has been reported by Owen et al (2001), and our Phoebe study appears in Owen et al (1999). In this paper, we present additional results from this program.…”

Section: Introductionmentioning

confidence: 66%

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A spectroscopic study of the surfaces of Saturn's large satellites: HO ice, tholins, and minor constituents

Cruikshank¹,

Owen²,

Ore³

et al. 2005

Icarus

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100

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We present spectra of Saturn's icy satellites Mimas, Enceladus, Tethys, Dione, Rhea, and Hyperion, 1.0-2.5 µm, with data extending to shorter (Mimas and Enceladus) and longer (Rhea and Dione) wavelengths for certain objects. The spectral resolution (R = λ/ λ) of the data shown here is in the range 800-1000, depending on the specific instrument and configuration used; this is higher than the resolution (R = 225 at 3 µm) afforded by the Visual-Infrared Mapping Spectrometer on the Cassini spacecraft. All of the spectra are dominated by water ice absorption bands and no other features are clearly identified. Spectra of all of these satellites show the characteristic signature of hexagonal H 2 O ice at 1.65 µm. We model the leading hemisphere of Rhea in the wavelength range 0.3-3.6 µm with the Hapke and the Shkuratov radiative transfer codes and discuss the relative merits of the two approaches to fitting the spectrum. In calculations with both codes, the only components used are H 2 O ice, which is the dominant constituent, and a small amount of tholin (Ice Tholin II). Tholin in small quantities (few percent, depending on the mixing mechanism) appears to be an essential component to give the basic red color of the satellite in the region 0.3-1.0 µm. The quantity and mode of mixing of tholin that can produce the intense coloration of Rhea and other icy satellites has bearing on its likely presence in many other icy bodies of the outer Solar System, both of high and low geometric albedos. Using the modeling codes, we also establish detection limits for the ices of CO 2 (a few weight percent, depending on particle size and mixing), CH 4 (same), and NH 4 OH (0.5 weight percent) in our globally averaged spectra of Rhea's leading hemisphere. New laboratory spectral data for NH 4 OH are presented for the purpose of detection on icy bodies. These limits for CO 2 , CH 4 , and NH 4 OH on Rhea are also applicable to the other icy satellites for which spectra are presented here. The reflectance spectrum of Hyperion shows evidence for a broad, unidentified absorption band centered at 1.75 µm.

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Section: Introductionmentioning

confidence: 66%

“…Tholins are strongly colored, and mostly affect the short wavelength portion (0.3-1.4 µm) of the spectrum, where H 2 O ice is nearly neutral in reflectance. Certain tholins have a strong N-H absorption band at 3 µm, which appears in the model spectra (note particularly the models of Iapetus in Owen et al, 2001).…”

Section: Rheamentioning

confidence: 98%

A spectroscopic study of the surfaces of Saturn's large satellites: HO ice, tholins, and minor constituents

Cruikshank¹,

Owen²,

Ore³

et al. 2005

Icarus

Self Cite

100

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“…Surfaces made up of organics exposed to high amounts of radiation (e.g., inner solar system, or older surfaces in the outer solar system) get darker and blacker (or grayer), whereas organic-containing surfaces exposed to less radiation are redder (Andronico et al 1987). This explanation has been used, for instance, to explain the (visible) gray color of Phoebe compared to the red color of the dark material on Iapetus (Strazzulla 1986; Thompson et al 1987;Allamandola et al 1988;Owen et al 2001) as well as the gray color of KBOs of large eccentricity with aphelions >70 AU compared to visibly redder, cold outer solar system KBOs (perihelion >40 AU; Tegler et al 2003). We postulate here that the corresponding trend in the UV is toward older, more weathered regions on Callisto becoming darker and the 350 nm absorption band strength decreasing, which tends to give the spectrum an overall redder slope in the UV.…”

Section: Discussionmentioning

confidence: 99%

Callisto: New Insights fromGalileoDisk‐resolved UV Measurements

Hendrix

Johnson

2008

Astrophysical Journal

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The entire set of observations from the Galileo Ultraviolet Spectrometer (UVS) is analyzed to look for spectral trends across the surface of Callisto, and to probe the spectral shapes in the near-UV. At low resolution, the leading hemisphere is slightly redder than the trailing hemisphere at k > 280 nm; this has been interpreted by past researchers to indicate the presence of SO 2 on the leading hemisphere. Here we point out that such an ''absorption feature'' can be induced when ratioing hemispherical spectra. High-resolution observations are used to detect the presence of an absorption band at high southern latitudes, interpreted to be due to some organic species that is weathered away (carbonized ) at lower latitudes. The presence of CO 2 in the surface and in the atmosphere of Callisto and the dark nature of the surface suggest that carbon-based species are present across the surface associated with either endogenic or delivered organics. These organics experience chemical modification by UV radiation and are mixed into the regolith by meteoritic bombardment. Subject headingg s: planets and satellites: general -planets and satellites: individual (Callisto) -ultraviolet: solar system

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“…Whether observed absorption bands in Centaur and KBO spectra (see, e.g., Brown 2000, Bauer et al 2002, and Barucci et al 2002 are caused by species that are intimately mixed or spatially variegated may not only significantly change the compositional fits to the spec-Vol. 610 tra but may also provide clues as to whether these species are exposed or implanted by exogenic or endogenic processes (Hainaut et al 2000;Owen et al 2001). Color and albedo correlations have broader implications regarding the reported color bimodality or gradients among outer solar system small bodies (e.g., Tegler & Romanishin 2003;Bauer et al 2003) and how to interpret these observed phenomena.…”

Section: Discussionmentioning

confidence: 99%

Recovering the Rotational Light Curve of Phoebe

Bauer

Buratti

Simonelli

et al. 2004

ApJ

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We present rotational light-curve data for Saturn's satellite Phoebe taken over the observing period prior to the Cassini mission's encounter with that moon. We find a rotation period of hr, a factor of 9.2735 ‫ע‬ 0.0006 25 improvement in the rotation period's uncertainty over previously published data. This improved rotation period measurement allow s us to correlate previously observed spectral features and colors with albedo features observed by Voyager and to predict which side of Phoebe will be observed by Cassini during its 2004 June 11 encounter. The light curve, sampled at subobserver latitudes farther south than achieved by Voyager, shows evidence of surface features that cannot be explained by previously published shape models or albedo maps and that may be located in the regions in Phoebe's southern hemisphere that were unobserved by Voyager.

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Decoding the Domino: The Dark Side of Iapetus

Cited by 80 publications

References 55 publications

A spectroscopic study of the surfaces of Saturn's large satellites: HO ice, tholins, and minor constituents

A spectroscopic study of the surfaces of Saturn's large satellites: HO ice, tholins, and minor constituents

Callisto: New Insights fromGalileoDisk‐resolved UV Measurements

Recovering the Rotational Light Curve of Phoebe

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