Density of Near Earth Asteroids

The density of near earth asteroids is a fundamental property which can illuminate the structure of the asteroid and is key in assessing the risk of an impact of an NEA with Earth. A low density can be indicative of a rubble pile structure whereas a higher density can imply a monolith and/or a higher metal content. Since the damage resulting from an impact of an asteroid with Earth depends on its interior structure and its total mass, density is a key parameter to understanding the risk of asteroid impact. Unfortunately, measuring the density of asteroids is extremely difficult, has only been attempted for a tiny fraction of NEAs and usually results in measurements with large uncertainties. In the absence of density measurements for a specific object, understanding the range and distribution of likely densities can allow for probabilistic assessment of the ensemble risk of an impact of an NEA and permit estimates of the range of reasonable masses for specific object. We have developed a candidate density distribution for near earth asteroids based on measurements of meteorite densities and an assumed range of macroporosities. Bayesian inference and existing near earth asteroid density measurements are used to develop an updated distribution.