Olivine-dominated A-type asteroids in the main belt: Distribution, abundance and relation to families

Abstract

Differentiated asteroids are rare in the main asteroid belt despite evidence for ∼100 distinct differentiated bodies in the meteorite record. We have sought to understand why so few main-belt asteroids differentiated and where those differentiated bodies or fragments reside. Using the Sloan Digital Sky Survey (SDSS) to search for a needle in a haystack we identify spectral A-type asteroid candidates, olivine-dominated asteroids that may represent mantle material of differentiated bodies. We have performed a near-infrared spectral survey with SpeX on the NASA IRTF and FIRE on the Magellan Telescope.We report results from having doubled the number of known A-type asteroids. We deduce a new estimate for the overall abundance and distribution of this class of olivine-dominated asteroids. We find A-type asteroids account for less than 0.16% of all main-belt objects larger than 2 km and estimate there are a total of ∼600 A-type asteroids above that size. They are found rather evenly distributed throughout the main belt, are even detected at the distance of the Cybele region, and have no statistically significant concentration in any asteroid family. We conclude the most likely implication is the few fragments of olivine-dominated material in the main belt did not form locally, but instead were implanted as collisional fragments of bodies that formed elsewhere.

Visible Spectroscopy from the Mission Accessible Near-Earth Object Survey (MANOS): Taxonomic Dependence on Asteroid Size

“…The last hypothesis would imply the fact that some asteroids are mistakenly defined as A-type if they are only observed in the visible. DeMeo et al (2019) found that only half of the A-types defined by the visible regime are actually A-types, when you observe them in the near-IR.…”

“…A-type asteroids are uncommon all over the mainasteroid belt. DeMeo et al (2019) reported fractions of A-types for the inner, mid, and outer main belt to be 0.22%, 0.14%, and 0.11% respectively. These values are more than 10 times lower than those found in the MANOS and NEOSHIELD2 database.…”

Physical and dynamical properties of the unusual V-type asteroid (2579) Spartacus

“…Dynamical studies (Carruba et al 2014;Huaman et al 2014) indicate seven source regions and thus seven possible parent bodies (or alternatively seven scattering events from Vesta). On the other hand, no V-or A-type asteroid clusters have been identified (DeMeo et al 2019;Burbine et al 2017) so far in the mid and outer main belt and the distribution of these bodies appears random. Brasil et al (2017) suggest that the "jumping-Jupiter" planetary migration scenario could perhaps explain the existence of some of those V-types in the middle main belt.…”

Characterization of D‐Type Spectra Based on Hyperspectral Remote Sensing of the Lunar Surface

“…We next compare the spectral features of the darkest, reddest sites, dark maria, and red maria to quantitative criteria for the standard asteroidal taxonomic classification (e.g., DeMeo & Carry, 2013; DeMeo et al., 2009, 2019). In the classification by DeMeo and Carry (2013) and DeMeo et al.…”

“…Thus, in this study, we first surveyed the (1) darkest and (2) reddest sites independently on the lunar surface, and examined the correlation among these features and the featurelessness of them, all of which are characteristics of D‐type spectra. We then conducted an asteroidal taxonomic classification for the spectral features of the darkest, reddest sites on the lunar surface based on the quantitative criteria (DeMeo & Carry, 2013; DeMeo et al., 2009, 2019). From these results, we discuss how the D‐type analog of rocky materials on the lunar surface is related to the spectral features of D‐type bodies, including Phobos and Deimos, classified in previous studies.…”