Rotationally Resolved Spectra of 10 Hygiea and a Spectroscopic Study of the Hygiea Family

doi:10.1006/icar.2001.6618

Icarus

Volume 152, Issue 1, July 2001, Pages 117-126

https://doi.org/10.1006/icar.2001.6618 Get rights and content

Abstract

Reflectance spectra of 10 objects belonging to the Hygiea family are presented for the first time in the wavelength range 4900–9200 Å. In this same range we report also the rotationally resolved spectrum of 10 Hygiea, the largest remnant of the family. 10 Hygiea is a C-type asteroid and one of the largest known C-type asteroids. A significant number of objects of the family seem to belong to the B taxonomic class of Tholen. This is in concordance with some degree of thermal metamorphism acting on the family's original parent body. Objects of other taxonomic types, namely three S-types and one D-type, are also present and are most probably interlopers in the family.

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Citation Excerpt :
The Vesta family famously dominates the inner asteroid belt with its numbers (Binzel and Xu, 1993; DeMeo and Carry, 2013), and was a critical piece of evidence in tying the HED meteorites to Vesta. Pallas, the second-largest asteroid, has a dynamical family (Gil-Hutton, 2006), Hygiea, the fourth-largest asteroid, is associated with a family (Nesvorny, 2012; Carruba, 2013; Mothé-Diniz et al., 2001, see Section 3.2 for further discussion of the Hygiea family), as is the largest S-class asteroid, 15 Eunomia (Nesvorny, 2012). Ceres is unassociated with any sort of family at all in our current understanding of dynamical groupings, which alone is perhaps not sufficient to draw any conclusion, but motivates us towards the considerations we make in this paper.
Ceres is unusual among large (>250 km) asteroids in lacking a dynamical family. We explore possible explanations, noting that its particularly large size and the ubiquity of families associated with other large asteroids makes avoidance of a sufficiently-sized collision by chance exceedingly unlikely. Current models of Ceres’ thermal history and interior structure favor a differentiated object with an icy near-surface covered by an ∼0.1–1 km lag deposit, which could result in a collisional family of diverse, predominately icy bodies. We predict that sublimation of an icy Ceres family would occur on timescales of hundreds of millions of years, much shorter than the history of the Solar System. Sublimation on a Ceres family body would be aided by a low non-ice fraction and a high average temperature, both of which would inhibit lag deposit development. Because there seems to be no likely mechanism for removing a rocky Ceres family, and because the formation of a Ceres family of some kind seems nearly statistically inevitable, the lack of a Ceres family is indirect but independent evidence for Ceres’ differentiation.
All of the other large asteroids lacking dynamical families (704 Interamnia, 52 Europa, and 65 Cybele) have spectral properties similar to Ceres, or otherwise suggesting ice at their surfaces. While other large asteroids with similar spectral properties do have families (24 Themis, 10 Hygiea, 31 Euphrosyne), their families are not well understood, particularly Hygiea.
Formation of brucite and cronstedtite-bearing mineral assemblages on Ceres
2014, Icarus
Citation Excerpt :
The age of the Hygiea family asteroids (2 ± 1 Gyr) is consistent with post-accretional collisions (Brož et al., 2013). The low spectral contrast of Ceres (e.g., Carry et al., 2012) and Hygiea (Mothé–Diniz et al., 2001) could reflect impact homogenization by impact surges and gravitational fallout of ejected materials, which may not be efficient on smaller asteroids. The fine-grained (dusty) and porous surface materials on Ceres (Section 1.1) and Hygiea (Lebofsky et al., 1985; Johnston et al., 1989) could be gravitationally-sorted impact deposits.
Dwarf planet Ceres is the largest body in the main asteroid belt with a rocky surface and uncertain internal structure. Spectra of Ceres in near- and mid-infrared wavelengths are consistent with the occurrence of brucite, Mg-bearing carbonates, and an Fe-rich phyllosilicate cronstedtite. Spectra of 10 Hygiea and 324 Bamberga imply similar compositions. Here, we considered stabilities of these minerals to constrain their origin. Cronstedtite is most stable at the temperature of ∼0 °C at moderately oxidizing aqueous conditions and at high water/rock ratios. Although cronstedtite could form on planetesimals, the apparent lack of serpentine may indicate its formation by Ceres’ temporary surface solutions. Brucite forms at a low activity of dissolved SiO₂, at a low fugacity of CO₂, and at highly alkaline pH. Brucite and cronstedtite do not form together and may not form deep in the Ceres’ interior. The absence of Mg serpentine from Ceres’ surface materials and the unlikely occurrence of very olivine-rich rocks do not indicate a formation of brucite through serpentinization of such rocks. Brucite could form by transient near-surface fluids which do not equilibrate with silicates. Temporary fluids could deposit Mg carbonates before, after, or together with brucite at near-surface conditions that favor CO₂ degassing. Regardless of Ceres’ internal structure, internal thermal and aqueous processes may not affect cold near-surface layers. Percolation of interior fluids is not consistent with the lack of detection of low-solubility salts. However, impacts of ice-rich targets during the Late Heavy Bombardment could account for transient aqueous environments and unusual surface mineralogies of Ceres, Hygiea, and Bamberga. Brucite and Mg carbonates could have formed through hydration and carbonation of MgO evaporated from silicates. Apparently abundant carbonates may indicate an ample impact oxidation of organic matter, and the occurrence of brucite with cronstedtite may reflect turbulent and disequilibrium environments. Clay-like homogeneous surface materials on Ceres could be gravitationally sorted deposits of impact clouds.
Asteroids
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Asteroids are some of the remaining planetesimals that helped form the terrestrial and Jovian planets. Asteroids, which are the parent bodies of almost all meteorites, are almost entirely observed remotely using Earth- and space-based telescopes with only a few bodies studied up close by spacecraft missions. This chapter will discuss what is currently known concerning asteroid chemistries from spectral reflectance observations from Earth, spectral reflectance and geochemical observations from spacecraft missions, and the successful Hayabusa sample return mission. These observations have allowed us to gain considerable insight on possible parent bodies of meteorites and the compositional structure of the solar nebula.
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2012, Icarus
The Sloan Digital Sky Survey (SDSS) Moving Object Catalog contains spectrophotometric information for thousands of asteroids, presenting the opportunity to probe objects much fainter than are typically reached in spectroscopic surveys. Using two different approaches, it is estimated that 30 ± 5% of the C-complex asteroids in the SDSS have a 0.7-μm band, implying that roughly two-thirds will have a 3-μm absorption band and hydrated minerals based on correlations between those two absorptions found by Howell et al. (Howell, E.S. et al. [2011]. EPSC-DPS Joint Meeting, p. 637). In an effort to avoid confusion with formal taxonomies, I call these objects $\tilde{Ch}$ in this work, with the $\tilde{C}$ group defined as those without evidence of a 0.7-μm band. This fraction appears fairly stable with solar distance, although there is evidence it is higher in the middle asteroid belt (2.50–2.82 AU) than outside those bounds. In the size range covered by the SDSS dataset, the $\tilde{Ch}$ fraction is most consistent with a flat distribution. Inclusion of the SMASS and S3OS2 datasets suggests an overall minimum in $\tilde{Ch}$ fraction from H ∼ 12–14, though this distribution may be biased by the solar distance variation mentioned above.
Spectral study of the Eunomia asteroid family Part II: The small bodies
2010, Icarus
Reflectance spectra in visible and near-infrared wavelengths of 97 nominal members of the Eunomia asteroid family have been obtained and analyzed. According to these investigations, 94% of the observed dynamic family members belong to the Tholen S-class, only 4% to the C-class and 2% to the M-class. The S-asteroids are believed to be “genetic” members of the Eunomia family and thus are fragments of 15 Eunomia. The fragments show different 1- and 2-μm absorption band characteristics, which are likely attributed to their place of origin within the parent body. The major volume fraction of the investigated members seems to originate from the “crust” of the parent body while the volume fraction of “mantle” material is less. Previous spectral investigations (Nathues, A., Mottola, S., Kaasalainen, M., Neukum, G. [2005], Icarus 175 (2), 452–463) of the family’s main body, 15 Eunomia, revealed variations of olivine and pyroxene on a hemispherical scale. These findings, together with the conclusion that the major mineral component of 15 Eunomia and its fragments is olivine, suggest that a large fraction of the original pyroxene-enriched crust layer has been lost due to a major collision that created the asteroid family. Significant spectral evidences consistent with high concentrations of metals have not been found in the rotational resolved spectra of 15 Eunomia and in its fragments. This led to the conclusion that either a core, which consists mainly of metals, does not exist or that an eventual one has not yet been unearthed by an impact. The absence of V-type asteroids, the low number of M-types among the dynamic family members and the lack of distinct feldspar absorption features in the S-asteroid spectra suggest that the parent body of the Eunomia family was partially differentiated rather than fully differentiated.
Reanalysis of asteroid families structure through visible spectroscopy
2005, Icarus
The taxonomic properties of the main asteroid families are analyzed and discussed in the light of an updated definition of the families using a large proper elements database and the asteroids taxonomy derived from reflectance spectra recently obtained by two large visible spectroscopic surveys: the SMASS II and the S3OS2. Our analysis indicates that most families are quite homogeneous taxonomically and mineralogically—whenever there exists a mineralogical constraint—, being probably originated from homogeneous parent bodies. The exceptions are the Nysa family, that should likely be considered a clan, and the Eos family that encompasses a broad range of taxonomies, whose mineralogical relations cannot be completely ruled out. Only in a few cases the families may be taxonomically distinguished from the background population. That is the case of the Minerva/Gefion, Adeona, Dora, Merxia, Hoffmeister, Koronis, Eos, and Veritas families. Some of the families presented in this work show a larger spectral diversity than previously reported, as it is the case for the Maria and Koronis families. On the other hand, the Veritas family is found to be homogeneous, in sharp contrast with previous works. Mineralogical relations are reported whenever they could be found in the literature and we examine the possible constraints posed by the presence of different taxonomies in certain families.

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^☆: Based on observations made with the 1.82-m telescope at the Padova--Asiago Observatory (Italy), the 2.2-m telescope at the European Southern Observatory (La Silla, Chile), and the 1.52-m telescope at the European Southern Observatory (La Silla, Chile) under agreement with the CNP_q/Observatório Nacional (Brazil).

^f1: [email protected]

²: Died on November 2, 1997 in a mountain accident. This paper is devoted to his memory.

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Regular ArticleRotationally Resolved Spectra of 10 Hygiea and a Spectroscopic Study of the Hygiea Family☆

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Pole coordinates and shape of 30 asteroids

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Rotationally Resolved Spectra of 10 Hygiea and a Spectroscopic Study of the Hygiea Family☆