Spectroscopic Survey of X-type Asteroids

TL;DR

This spectroscopic survey of 24 X-type asteroids reveals diverse spectral features and suggests mineralogies, including metallic and meteorite analogues, expanding understanding of asteroid compositions within the X class.

Contribution

The study provides new near-infrared spectra and classifications for X-type asteroids, identifying mineralogies and proposing revised taxonomic assignments based on spectral and albedo data.

Findings

Identification of weak absorption bands in 11 asteroids

Many M-types fit with metallic iron or pallasite meteorites

C/P-types best match CM meteorites with heating or irradiation

Abstract

We present reflected light spectral observations from 0.4 to 2.5 micron of 24 asteroids chosen from the population of asteroids initially classified as Tholen X-type objects (Tholen, 1984). The X complex in the Tholen taxonomy comprises the E, M and P classes which have very different inferred mineralogies but which are spectrally similar to each other, with featureless spectra in visible wavelengths. The data were obtained during several observing runs in the 2004-2007 years at the NTT, TNG and IRTF telescopes. We find a large variety of near-infrared spectral behaviors within the X class, and we identify weak absorption bands in spectra of 11 asteroids. Our spectra, together with albedos published by Tedesco et al. (2002), can be used to suggest new Tholen classifications for these objects. In order to constrain the possible composition of these asteroids, we perform a least-squares search through the RELAB spectral database. Many of the best fits are consistent with meteorite analogue materials suggested in the published literature. In fact, we find that 7 of the new M-types can be fit with metallic iron (or pallasite) materials, and that the low albedo C/P-type asteroids are best fitted with CM meteorites, some of which have been subjected to heating episodes or laser irradiation. Finally, we consider and analyse the sample of the X-type asteroids we have when we combine the present observations with previously published observations for a total of 72 bodies.