Surface composition and temperature of the TNO Orcus

Barucci, M. A.; Merlin, F.; Guilbert, A.; Bérgh, C. de; Álvarez-Candal, A.; Hainaut, Olivier; Doressoundiram, A.; Dumas, Christophe; Owen, T.; Coradini, A.

doi:10.1051/0004-6361:20079079

Cited by 73 publications

(82 citation statements)

References 27 publications

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“…1) and is expected to be a spherical object, it is reasonable to think that the surface properties are rather homogeneous over the surface in the optical. In the near-infrared, according to the most recent, higher SNR data (Barucci et al 2008, and this work), crystalline water ice was always present (and in the same roughly proportions as in the indicative Hapke modeling). A 2.2 μm feature was also systematically shown to be there in the most recent works, with slightly different structures, although we believe they are roughly consistent within the noise.…”

Section: Surface Composition Variations Over Time?supporting

confidence: 76%

“…According to this model, Orcus should have lost all its volatile content. However, traces of methane (to be confirmed) could explain the near-infrared spectrum of Orcus (Barucci et al 2008). This object can therefore provide key constraints on the current surface volatile inventory of intermediate-size KBOs.…”

Section: Introductionmentioning

confidence: 85%

“…Additional spectroscopic observations of Orcus in the near infrared (H + K band only, from Barucci et al 2008) showed deep absorption features at 1.5 and 2.0 μm and shallow bands at 1.65 μm and close to 2.2 μm. The presence of crystalline water ice is evident in the 1.65 μm feature.…”

Section: The Choice Of the Chemical Componentsmentioning

confidence: 94%

“…Only traces of methane and ammonia are sufficient to significantly improve the fit with respect to a simple water ice mixture. We tested the mixtures used by Barucci et al (2008) against our data, i.e. trying separately methane, then ammonia hydrate (respectively mixed with water ice) but obtained a worse fit than models 2 and 3.…”

Section: Adding Methane and Ammonia Icesmentioning

confidence: 99%

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Methane, ammonia, and their irradiation products at the surface of an intermediate-size KBO?

Delsanti¹,

Merlin²,

Guilbert-Lepoutre³

et al. 2010

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Orcus is an intermediate-size 1000 km-scale Kuiper belt object (KBO) in 3:2 mean-motion resonance with Neptune, in an orbit very similar to that of Pluto. It has a water-ice dominated surface with solar-like visible colors. We present visible and near-infrared photometry and spectroscopy obtained with the Keck 10 m-telescope (optical) and the Gemini 8 m-telescope (near-infrared). We confirm the unambiguous detection of crystalline water ice as well as absorption in the 2.2 μm region. These spectral properties are close to those observed for Pluto's larger satellite Charon, and for Plutino (208996) 2003 AZ 84 . Both in the visible and near-infrared Orcus' spectral properties appear to be homogeneous over time (and probably rotation) at the resolution available. From Hapke radiative transfer models involving intimate mixtures of various ices we find for the first time that ammonium (NH + 4 ) and traces of ethane (C 2 H 6 ), which are most probably solar irradiation products of ammonia and methane, and a mixture of methane and ammonia (diluted or not) are the best candidates to improve the description of the data with respect to a simple water ice mixture (Haumea type surface). The possible more subtle structure of the 2.2 μm band(s) should be investigated thoroughly in the future for Orcus and other intermediate size Plutinos to better understand the methane and ammonia chemistry at work, if any. We investigated the thermal history of Orcus with a new 3D thermal evolution model. Simulations over 4.5×10 9 yr with an input 10% porosity, bulk composition of 23% amorphous water ice and 77% dust (mass fraction), and cold accretion show that even with the action of long-lived radiogenic elements only, Orcus should have a melted core and most probably suffered a cryovolcanic event in its history which brought large amounts of crystalline ice to the surface. The presence of ammonia in the interior would strengthen the melting process. A surface layer of a few hundred meters to a few tens of kilometers of amorphous water ice survives, while most of the remaining volume underneath contains crystalline ice. The crystalline water ice possibly brought to the surface by a past cryovolcanic event should still be detectable after several billion years despite the irradiation effects, as demonstrated by recent laboratory experiments.

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Section: Surface Composition Variations Over Time?supporting

confidence: 76%

Section: Introductionmentioning

confidence: 85%

Section: The Choice Of the Chemical Componentsmentioning

confidence: 94%

Section: Adding Methane and Ammonia Icesmentioning

confidence: 99%

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Methane, ammonia, and their irradiation products at the surface of an intermediate-size KBO?

Delsanti¹,

Merlin²,

Guilbert-Lepoutre³

et al. 2010

A&A

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“…The free parameters of our models are the grain size and the relative amount of each chemical compound. The lowest reduced χ 2 values between the observed spectra and our synthetic spectra were reached using the Marqvardt-Levenberg algorithm, although it is important to note that our model results are not unique and only show the most probable surface composition from our initial set of probable chemical analogs (see Barucci et al 2008a, on a discussion of the limits of this model).…”

Section: Spectral Modelingmentioning

confidence: 81%

High-contrast observations of (136108) Haumea

Dumas¹,

Carry²,

Hestroffer³

et al. 2011

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Context. The trans-Neptunian region of the Solar System is populated by a wide variety of icy bodies showing great diversity in orbital behavior, size, surface color, and composition. One can also see there are dynamical families and binary systems. One surprising feature detected in the spectra of some of the largest trans-Neptunians is the presence of crystalline water-ice. This is the case for the large TNO (136 108) Haumea (2003 EL 61 ). Aims. We seek to constrain the state of the water ice of Haumea and its satellites and to investigate possible energy sources that maintain the water ice in its crystalline form. Methods. Spectro-imaging observations in the near infrared were performed with the integral field spectrograph SINFONI mounted on UT4 at the ESO Very Large Telescope. The spectra of both Haumea and its larger satellite Hi'iaka were analyzed. Relative astrometry of the components was also measured, providing a check of the orbital solutions and equinox seasons. Results. We describe the physical characteristics of the crystalline water-ice present on the surface of Haumea and its largest satellite Hi'iaka and analyze possible sources of heating to maintain water in a crystalline state: tidal dissipation in the system components vs. radiogenic source. The surface of Hi'iaka appears to be covered by large grains of water ice, almost entirely in its crystalline form. Under some restricted conditions, both radiogenic heating and tidal forces between Haumea and Hi'iaka could provide the energy needed to maintain the ice in its crystalline state.

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