Surface Composition of (99942) Apophis

TL;DR

This study provides high-quality near-infrared spectral data of asteroid Apophis, analyzes its surface composition, and discusses implications for seismic activity during its 2029 close approach to Earth.

Contribution

It presents the most detailed pre-encounter spectral analysis of Apophis, using a naive Bayes classifier to estimate its composition and potential surface changes during the 2029 flyby.

Findings

Spectral data consistent with previous observations but with higher signal-to-noise ratio.

Likelihood of Apophis being an LL chondrite >99%.

Estimated source region in the inner main belt.

Abstract

On April 13, 2029, near-Earth asteroid (NEA) (99942) Apophis will pass at a distance of 6 Earth radii from Earth. This event will provide researchers with a unique opportunity to study the effects of tidal forces experienced by an asteroid during a close encounter with a terrestrial planet. Binzel et al. (2010) predicted that close flybys of terrestrial planets by NEAs would cause resurfacing of their regolith due to seismic shaking. In this work we present the best pre-encounter near-infrared spectra of Apophis obtained so far. These new data were obtained during the 2013 apparition using the NASA Infrared Telescope Facility (IRTF). We found that our spectral data is consistent with previous observations by Binzel et al. (2009) but with a much higher signal-to-noise ratio. Spectral band parameters were extracted from the spectra and were used to determine the composition of the asteroid. Using a naive Bayes classifier, we computed the likelihood of Apophis being an LL chondrite to be >99% based on mol% of Fa vs. Fs. Using the same method, we estimated a probability of 89% for Apophis being an LL chondrite based on ol/(ol+px) and Fs. The results from the dynamical model indicate that the most likely source region for Apophis is the nu6 resonance in the inner main belt. Data presented in this study (especially Band I depth) could serve as a baseline to verify seismic shaking during the 2029 encounter.