Taxonomic analysis of asteroids with artificial neural networks

ABSTRACT We study the surface composition of asteroids with visible and/or infrared spectroscopy. For example, asteroid taxonomy is based on the spectral features or multiple color indices in visible and nearinfrared wavelengths. The composition of asteroids gives key information to understand their origin and evolution. However, we lack compositional information for faint asteroids due to limits of groundbased observational instruments. In the near future, the Chinese Space Survey telescope (CSST) will provide multiple colors and spectroscopic data for asteroids of apparent magnitude brighter than 25 mag and 23 mag, respectively. For the aim of analysis of the CSST spectroscopic data, we applied an algorithm using artificial neural networks (ANNs) to establish a preliminary classification model for asteroid taxonomy according to the design of the survey module of CSST. Using the SMASS II spectra and the Bus-Binzel taxonomy system, our ANN classification tool composed of 5 individual ANNs is constructed, and the accuracy of this classification system is higher than 92 %. As the first application of our ANN tool, 64 spectra of 42 asteroids obtained in 2006 and 2007 by us with the 2.16-m telescope in the Xinglong station (Observatory Code 327) of National Astronomical Observatory of China are analyzed. The predicted labels of these spectra using our ANN tool are found to be reasonable when compared to their known taxonomic labels. Considering the accuracy and stability, our ANN tool can be applied to analyse the CSST asteroid spectra in the future. INTRODUCTION Small Solar System objects S3Os are thought to be remnants of planetesimals from the early stage of the planetary formation of the Solar System. Compared to the planets, the S3Os could retain more information of protoplanetary conditions because of suffering less secondary chemical and geological evolution, although they have undergone collisions, space weathering, and dynamical and thermal evolution, which shaped their present physical and orbital properties (DeMeo & Carry 2014). At present, most discovered S3Os are asteroids which are thought to originate from the inner planetesimals, as the building blocks of the terrestrial planets. The composition of asteroids vs. their orbits can provide some clues to the origin and the evolution of asteroids, as well as the constraints on planetary formation models in the inner Solar System (Bottke et al. 2002).