Spectra of extremely reduced assemblages: Implications for Mercury

. Visible and near infrared spectroscopic investigation of E-type asteroids, including 2867 Steins, a target of the Rosetta mission. Icarus, Elsevier, 2009, 196 (1) This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. AbstractWe present the results of a visible spectroscopic and photometric survey of igneous asteroids belonging to the small and intriguing Eclass, including 2867 Steins, a target of the Rosetta mission. The survey was carried out at the 3.5m Telescopio Nazionale Galileo (TNG), and at the 3.5m New Technology Telescope (NTT) of the European Southern Observatory. We obtained new visible spectra for eighteen E-type asteroids, and near infrared spectra for eight of them. We confirm the presence of three different mineralogies in the small E-type populations. We classify each object in the E To fully investigate the E-type population, we enlarged our sample including 6 E-type asteroids spectra available in literature, resulting in a total sample of 21 objects. The analysis of the spectral slope for the 3 different E-type subgroups versus the orbital elements show that E[III] members have the lowest mean spectral slope value inside the whole sample, and that they are located between 2.2-2.7 AU in low inclination orbits. E[II] members has the highest spectral slope inside the sample, half of them are located in the Hungaria region, 2 are NEA and 2 (64 Angelina and 2867 Steins), are in the main belt. A similar distribution is found for the 5 featureless E[I] members, located mainly in the Hungaria region (3 members), one in the middle main belt while one is a NEA (2004 VD17). Finally, for the five E-type asteroids observed both in the visible and near infrared range, plus 2867 Steins, we attempt to model their surface composition using linear geographycal mixtures of no more than 3 components, selected from aubrite meteorites and correlated minerals. In particular we suggest that the aubrite Peña Blanca might have the E[III] asteroid 317 Roxane as parent body, and that the aubrite ALH78113 might be related to the E[II] subgroup asteroids.

Section: Accepted M Manuscriptmentioning

confidence: 84%

Section: Accepted M Manuscriptmentioning

confidence: 97%

Visible and near infrared spectroscopic investigation of E-type asteroids, including 2867 Steins, a target of the Rosetta mission☆

Fornasier

Migliorini

Dotto

et al. 2008

“…On this basis, it has been suggested that hollow-formation involves the loss of the 'darkening' agent within LRM [Blewett et al, 2013], which may be spectrally neutral (making LRM relatively 'blue' by counteracting the 'redness' of other components) [Blewett et al, 2009]. Calcium or magnesium sulfides are most commonly-cited as candidates for the relatively volatile substance [Blewett et al, 2011[Blewett et al, , 2013Helbert et al, 2012], on the basis of the high concentration of sulfur detected at Mercury's surface [Nittler et al, 2011;Evans et al, 2012], expectations for mineralogy under Mercury's highly reducing conditions [Burbine et al, 2002], and correlations between sulfur, calcium and magnesium abundance in heavily-cratered terrains [Weider et al, 2015]. This hypothesis has recently gained further support from observations of anomalously high exospheric calcium above the extensively-hollowed Tyagaraja crater [Bennett et al, 2016].…”

Section: Introductionmentioning

confidence: 99%

Mercury's low-reflectance material: Constraints from hollows

Thomas

Hynek

Rothery

et al. 2016

Highlights We investigate the composition of Mercury's deep volatile-rich low-reflectance layer. Reflectance spectra of lag on sublimation hollow floors within it provide constraints. Analysis supports volatile (Mg,Ca) sulfides and non-volatile graphite within LRM. Unusually low reflectance material, within which depressions known as hollows appear to be actively forming by sublimation, is a major component of Mercury's surface geology. The observation that this material is exhumed from depth by large impacts has the intriguing implication that the planet's lower crust or upper mantle contains a significant volatile-rich, lowreflectance layer, the composition of which will be key for developing our understanding of Mercury's geochemical evolution and bulk composition. Hollows provide a means by which the composition of both the volatile and non-volatile components of the low-reflectance material (LRM) can be constrained, as they result from the loss of the volatile component, and any remaining lag can be expected to be formed of the non-volatile component. However, previous work has approached this by investigating the spectral character of hollows as a whole, including that of bright deposits surrounding the hollows, a unit of uncertain character. Here we use high-resolution multispectral images, obtained as the MESSENGER spacecraft approached Mercury at lower altitudes in the latter part of its mission, to investigate reflectance spectra of inactive hollow floors where sublimation appears to have ceased, and compare this to those of the bright surrounding products and the parent material. This analysis reveals that the final lag after hollow-formation has a flatter spectral slope than that of any other unit on the planet and reflectance approaching that of more space-weathered parent material. This indicates firstly that the volatile material lost has a steeper spectral slope and higher reflectance than the parent material, consistent with (Ca,Mg) sulfides, and secondly, that the low-reflectance component of LRM is non-volatile and may be graphite.

“…This observational technique, which utilizes the wavelength region from ~0.7-2.5-µm, is the main technique used to remotely study Mercury, Earth's Moon, and small solar system bodies such as the main-belt asteroids (e.g., Gaffey et al, 1993;Pieters et al, 2000;Burbine et al, 2002;Vernazza et al, 2010;Clark et al, 2011;Emery et al, 2011;Reddy et al, 2011;Lindsay et al, 2013;Rivkin et al, 2013). This technique is useful because it focuses on the spectral region where an object's primary surface mineralogy usually dominates over secondary effects, such as grain size variations, space weathering, observational variables, etc.…”

Section: Goal 2 -Mineralogical Characterization Of V P -Type Asteroidsmentioning

confidence: 99%

More chips off of Asteroid (4) Vesta: Characterization of eight Vestoids and their HED meteorite analogs

Hardersen

Reddy

Roberts

et al. 2014

Vestoids are generally considered to be fragments from Asteroid (4) Vesta that were ejected by past collisions that document Vesta's collisional history. Dynamical Vestoids are defined by their spatial proximity with Vesta (Zappala et al., 1995;Nesvorny et al., 2012). Taxonomic Vestoids are defined as V-type asteroids that have a photometric, visible-wavelength spectral, or other observational relationship with Vesta (Tholen, 1984; Bus and Binzel, 2002; Carvano et al., 2010). We define 'genetic Vestoids' as V-type asteroids that are probable fragments ejected from (4) Vesta based on the supporting combination of dynamical, near-infrared (NIR) spectral, and taxonomic evidence. NIR reflectance spectroscopy is one of the primary ground-based techniques to constrain an asteroid's major surface mineralogy (Burns, 1993a). Despite the reasonable likelihood that many dynamical and taxonomic Vestoids likely originate from Vesta, ambiguity exists concerning the fraction of these populations that are from Vesta as compared to the fraction of asteroids that might not be related to Vesta.Currently, one of the most robust techniques to identify the genetic Vestoid population is through NIR reflectance spectroscopy from ~0.7-2.5 µm. The derivation of spectral band parameters, and the comparison of those band parameters with those from representative samples from the Howardite-Eucrite-Diogenite (HED) meteorite types, allows a direct comparison of their primary mineralogies. Establishing tighter constraints on the genetic Vestoid population will better inform mass estimates for the current population of probable Vestoids, will provide more accurate orbital information of Vestoid migration through time that will assist dynamical models, and will constrain the Icarus, accepted for publication, August 12, 2014 3 overall current abundance of basaltic material in the main asteroid belt (Moskovitz et al., 2008).This work reports high-quality NIR spectra, and their respective interpretations, for eight V p -type asteroids, as defined by Carvano et al. (2010), that were observed at the