The size, shape, density, and Albedo of Ceres from its occultation of BD+8°471

Millis, R. L.; Wasserman, L. H.; Franz, O. G.; Nye, R.; Oliver, R. G.; Kreidl, T. J.; Jones, Steven E.; Hubbard, W. B.; Lebofsky, L. A.; Goff, R. W.; Marcialis, R. L.; Sykes, M. V.; Frecker, J. E.; Hunten, D. M.; Zellner, B.; Reitsema, H. J.; Schneider, Glenn; Dunham, E. W.; Klavetter, J. J.; Meech, К. J.; Oswalt, T. D.; Rafert, J. B.; Strother, E. F.; Smith, J. Allyn; Povenmire, H.; Jones, Barrie W.; Kornbluh, D.; Reed, Laureen G.; Izor, K.; A’Hearn, Michael F.; Schnurr, R.; Osborn, W.; Parker, David; Douglas, W.T.; Beish, J. D.; Klemola, A. R.; Ríos, M. de los; Sánchez, A.; Piironen, J.; Mooney, M.; Ireland, R.; Leibow, D.

doi:10.1016/0019-1035(87)90048-0

Cited by 72 publications

(36 citation statements)

References 11 publications

(10 reference statements)

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“…Although the results are generally consistent with each other, the differences encompass a broad range of (a − c) values that overlap around 33-35 km, as shown in Table 1 (Millis et al 1987;Thomas et al 2005;Drummond & Christou 2008;Carry et al 2008;Drummond et al 2014). These studies are based on three different techniques: star occultation (Millis et al 1987), visible imaging with the Hubble Space Telescope (HST; Thomas et al 2005), and ground-based adaptive optics (AO) for the other references. Differences between the inferred shape models are in part due to the difference in the surface coverage enabled by the various techniques.…”

Section: Test Casessupporting

confidence: 73%

Third-order development of shape, gravity, and moment of inertia for highly flattened celestial bodies. Application to Ceres

Rambaux

Chambat

Castillo‐Rogez

2015

A&A

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Context. We investigate the hydrostatic shape and gravitational potential coefficients of self-gravitating and rotating bodies large enough to have undergone internal differentiation and chemical stratification. Quantifying these properties under the assumption of hydrostatic equilibrium forms the basis for interpreting shape and gravity data in terms of interior structure and infer deviations from hydrostaticity that can bring information on the thermal and chemical history of the objects. Aims. The main purpose is to show the importance of developing the reference hydrostatic shape for relatively fast rotating bodies up to third order to reach an accuracy of a few tens of meters. This paper especially focuses on Ceres, for which high-resolution shape data are being obtained by the Dawn spacecraft, with a projected accuracy better than 200 m/pixel. Methods. To improve the accuracy on the determination of geodetic parameters, we numerically integrated Clairaut's equations of rotational equilibrium expanded up to third order in a small parameter m, the geodetic parameter.Results. Previous studies of Ceres have been based on shape models developed to first order. However, we show that the first-order theory underestimates (a − c) (where a and c are the equatorial and polar radii) by 1.8 km, which leads to underestimating the extent of mass concentration and is insufficient to interpret the upcoming observations by Dawn space mission. Instead, by using the third-order theory, we obtain an accuracy of 25 meters that is better than the accuracy expected from Dawn. Then, we derive the following geodetical quantities: flattening and other shape parameters, gravitational potential coefficients, and moments of inertia, by using the Ceres models constrained by observations obtained with the Hubble Space Telescope and ground-based adaptive optics telescopes. The difference in equatorial and polar radii for a large parametric space of interior models is investigated, and the large (a − c) corresponds to a model with a low density contrast. Conclusions. This type of modeling will also prove instrumental to infer non-hydrostatic contributions to Ceres' shape that are to be measured by Dawn.

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Section: Test Casessupporting

confidence: 73%

Third-order development of shape, gravity, and moment of inertia for highly flattened celestial bodies. Application to Ceres

Rambaux

Chambat

Castillo‐Rogez

2015

A&A

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“…These values are different from HST's by ∼10 km (relative difference of two percent). In comparison, the agreement between our semi-major axis and the determination made from stellar occultation by Millis et al (1987) is remarkable: 479.6 ± 2.4 km (occultation) vs. 479.7 ± 2.3 km (Keck), while our minor-axis value differ from theirs by ∼6-9 km (Table 5). Whereas Millis et al (1987) assumed a zeroobliquity at the time of the occultation, our SVC solution gives a SEP ϕ of +3.3…”

Section: Dimensionsmentioning

confidence: 65%

“…• range in the plane of the sky during the 1995 opposition as reported by Parker et al (2002), based on the compilation of Johnson et al (1983), Millis et al (1987), Saint-Pé et al (1993) and Drummond et al (1998) pole solutions). This situation changed dramatically with the use of highcontrast direct imaging techniques capable of resolving the disk of Ceres and image fine details on its surface, such as AO observations (e.g.…”

Section: Spin Vector Coordinatesmentioning

confidence: 99%

Near-infrared mapping and physical properties of the dwarf-planet Ceres

Carry

Dumas

Fulchignoni

et al. 2007

A&A

104

115

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Aims. We study the physical characteristics (shape, dimensions, spin axis direction, albedo maps, mineralogy) of the dwarf-planet Ceres based on high angular-resolution near-infrared observations. Methods. We analyze adaptive optics J/H/K imaging observations of Ceres performed at Keck II Observatory in September 2002 with an equivalent spatial resolution of ∼50 km. The spectral behavior of the main geological features present on Ceres is compared with laboratory samples. Results. Ceres' shape can be described by an oblate spheroid (a = b = 479.7 ± 2.3 km, c = 444.4 ± 2.1 km) with EQJ2000.0 spin vector coordinates α 0 = 288• ± 5• and δ 0 = +66 • ± 5• . Ceres sidereal period is measured to be 9.074 10 +0.000 10 −0.000 14 h. We image surface features with diameters in the 50-180 km range and an albedo contrast of ∼6% with respect to the average Ceres albedo. The spectral behavior of the brightest regions on Ceres is consistent with phyllosilicates and carbonate compounds. Darker isolated regions could be related to the presence of frost.

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“…Millis et al [1987] reported a V(λ = 560nm) geometric albedo of 0.073. Parker et al [2002] calculated geometric albedos of 0.056 near-UV (λ = 363.6nm), 0.029 mid-UV (λ= 279.5nm), and 0.090 far-UV (λ = 162.1nm).…”

Section: Ceresmentioning

confidence: 99%

Dawn: A journey in space and time

Russell¹,

Coradini²,

Christensen³

et al. 2004

Planetary and Space Science

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By successively orbiting both 4 Vesta and 1 Ceres the Dawn mission directly addresses the long-standing goals of understanding the origin and evolution of the solar system. Ceres and Vesta are two complementary terrestrial protoplanets (one apparently "wet" and the other "dry"), whose accretion was probably terminated by the formation of Jupiter. They provide a bridge in our understanding between the rocky bodies of the inner solar system and the icy bodies of the outer solar system. Ceres appears to be undifferentiated while Vesta has experienced significant heating and likely differentiation. Both formed very early in the history of the solar system and while suffering many impacts have remained intact, thereby retaining a record of events and processes from the time of planet formation. Detailed study of the geophysics and geochemistry of these two bodies provides critical benchmarks for early solar system conditions and processes that shaped its subsequent evolution. Dawn provides the missing context for both primitive and evolved meteoritic data, thus playing a central role in understanding terrestrial planet formation and the evolution of the asteroid belt. Dawn is to be launched in May 2006 arriving at Vesta in 2010 and Ceres in 2014, stopping at each to make 11 months of orbital measurements. The spacecraft uses solar electric propulsion, both in cruise and in orbit, to make most efficient use of its xenon propellant. The spacecraft carries a framing camera, visible and infrared mapping spectrometer, gamma ray/neutron spectrometer, magnetometer, and radio science.3

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The size, shape, density, and Albedo of Ceres from its occultation of BD+8°471

Cited by 72 publications

References 11 publications

Third-order development of shape, gravity, and moment of inertia for highly flattened celestial bodies. Application to Ceres

Third-order development of shape, gravity, and moment of inertia for highly flattened celestial bodies. Application to Ceres

Near-infrared mapping and physical properties of the dwarf-planet Ceres

Dawn: A journey in space and time

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