The Strength and Detectability of the YORP Effect in Near-Earth Asteroids: A Statistical Approach

TL;DR

This paper introduces a Monte Carlo method to estimate the YORP effect's strength and detectability on near-Earth asteroids using their orbital and size data, aiding observational planning and understanding rotational evolution.

Contribution

It presents a novel statistical approach to estimate YORP-induced rotational accelerations and their detectability without detailed shape models of asteroids.

Findings

YORP detectability depends on orbital and size properties.

Median YORP acceleration can be estimated from orbital parameters and diameter.

The required observational campaign length can be predicted for detection success.

Abstract

In addition to collisions and gravitational forces, it is now becoming widely acknowledged that photon recoil forces and torques from the asymmetric reflection and thermal re-radiation of sunlight are primary mechanisms that govern the rotational evolution of an asteroid. The Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect causes changes in the rotation rate and pole direction of an irregularly shaped asteroid. We present a simple Monte Carlo method to estimate the range of YORP-rotational-accelerations acting on a near-Earth asteroid (NEA) without knowledge of its detailed shape, and to estimate its detectability using light-curve observations. The method requires knowledge of an asteroid's orbital properties and size, and assumes that the future observational circumstances of an asteroid have already been thought through. It is verified by application to the observational circumstances of the seven YORP-investigated asteroids, and is then applied to 540 NEAs with NEOWISE and/or other diameter measurements, and to all NEAs using MPCORB absolute magnitudes. The YORP-detectability is found to be a strong function of the combined asteroid orbital and diameter properties, and is independent of the rotation period for NEAs that don't have very fast or slow rotation rates. The median and 1-sigma spread of YORP-rotational-acceleration expected to be acting on a particular NEA can be estimated from its semimajor axis, eccentricity, and diameter by using (eq. 1) and/or by using (eq. 2) if the diameter is instead estimated from the absolute magnitude by assuming a geometric albedo of 0.1. The length of a light-curve observational campaign required to achieve a 50 per cent probability of detecting the YORP effect in a particular NEA can be estimated by using (eq. 3) and/or by using (eq. 4) for an absolute-magnitude-estimated diameter.