Photometry and Polarimetry of 2010 XC$_{15}$: Observational Confirmation of E-type Near-Earth Asteroid Pair

TL;DR

This study confirms the existence of an E-type near-Earth asteroid pair, 2010 XC$_{15}$ and 1998 WT$_{24}$, through photometric and polarimetric observations, providing insights into their surface properties and possible formation via rotational fission.

Contribution

First confirmation of an E-type NEA pair using combined photometric and polarimetric data, suggesting a common origin and formation mechanism.

Findings

2010 XC$_{15}$ is an E-type NEA with specific color indices.

2010 XC$_{15}$ and 1998 WT$_{24}$ form the first confirmed E-type NEA pair.

The pair likely formed through rotational fission and originated from the main belt.

Abstract

Asteroid systems such as binaries and pairs are indicative of physical properties and dynamical histories of the Small Solar System Bodies. Although numerous observational and theoretical studies have been carried out, the formation mechanism of asteroid pairs is still unclear, especially for near-Earth asteroid (NEA) pairs. We conducted a series of optical photometric and polarimetric observations of a small NEA 2010 XC$_{15}$ in 2022 December to investigate its surface properties. The rotation period of 2010 XC$_{15}$ is possibly a few to several dozen hours and color indices of 2010 XC$_{15}$ are derived as $g-r=0.435\pm0.008$, $r-i=0.158\pm0.017$, and $r-z=0.186\pm0.009$ in the Pan-STARRS system. The linear polarization degrees of 2010 XC$_{15}$ are a few percent at the phase angle range of 58$^{\circ}$ to 114$^{\circ}$. We found that 2010 XC$_{15}$ is a rare E-type NEA on the basis of its photometric and polarimetric properties. Taking the similarity of not only physical properties but also dynamical integrals and the rarity of E-type NEAs into account, we suppose that 2010 XC$_{15}$ and 1998 WT$_{24}$ are of common origin (i.e., asteroid pair). These two NEAs are the sixth NEA pair and first E-type NEA pair ever confirmed, possibly formed by rotational fission. We conjecture that the parent body of 2010 XC$_{15}$ and 1998 WT$_{24}$ was transported from the main-belt through the $\nu_6$ resonance or Hungaria region.