The Albedo Distribution of Near Earth Asteroids

TL;DR

This study analyzes the albedo distribution of Near Earth Asteroids observed by WISE, revealing a bimodal distribution with dark and moderately dark populations, impacting detection strategies for potentially hazardous asteroids.

Contribution

It introduces a novel three-parameter model fitting the albedo distribution of NEAs, highlighting the existence of two distinct populations and their implications for asteroid detection.

Findings

25.3% of NEAs are in a very dark population peaking at p_V=0.03

74.7% of NEAs are in a moderately dark population peaking at p_V=0.168

Dark asteroids are harder to detect, affecting survey completeness goals.

Abstract

The cryogenic WISE mission in 2010 was extremely sensitive to asteroids and not biased against detecting dark objects. The albedos of 428 Near Earth Asteroids (NEAs) observed by WISE during its fully cryogenic mission can be fit quite well by a 3 parameter function that is the sum of two Rayleigh distributions. The Rayleigh distribution is zero for negative values, and follows $f(x) = x \exp[-x^2/(2\sigma^2)]/\sigma^2$ for positive x. The peak value is at x=\sigma, so the position and width are tied together. The three parameters are the fraction of the objects in the dark population, the position of the dark peak, and the position of the brighter peak. We find that 25.3% of the NEAs observed by WISE are in a very dark population peaking at $p_V = 0.03$, while the other 74.7% of the NEAs seen by WISE are in a moderately dark population peaking at $p_V = 0.168$. A consequence of this bimodal distribution is that the Congressional mandate to find 90% of all NEAs larger than 140 m diameter cannot be satisfied by surveying to H=22 mag, since a 140 m diameter asteroid at the very dark peak has H=23.7 mag, and more than 10% of NEAs are darker than p_V = 0.03.