Physical Properties of Near-Earth Asteroid 2011 MD

TL;DR

This study uses infrared observations and modeling to determine the physical characteristics of near-Earth asteroid 2011 MD, revealing it to be a small, highly porous rubble-pile asteroid with specific size, albedo, and density estimates.

Contribution

First detailed physical characterization of asteroid 2011 MD using infrared data and thermophysical modeling, providing size, density, and porosity estimates.

Findings

Diameter estimated at 6 (+4/-2) meters.

Bulk density around 1.1 (+0.7/-0.5) g/cm^3.

High macroporosity (>65%) indicating a rubble-pile structure.

Abstract

We report on observations of near-Earth asteroid 2011 MD with the Spitzer Space Telescope. We have spent 19.9 h of observing time with channel 2 (4.5 {\mu}m) of the Infrared Array Camera and detected the target within the 2{\sigma} positional uncertainty ellipse. Using an asteroid thermophysical model and a model of nongravitational forces acting upon the object we constrain the physical properties of 2011 MD, based on the measured flux density and available astrometry data. We estimate 2011 MD to be 6 (+4/-2) m in diameter with a geometric albedo of 0.3 (+0.4/-0.2) (uncertainties are 1{\sigma}). We find the asteroid's most probable bulk density to be 1.1 (+0.7/-0.5) g cm^{-3}, which implies a total mass of (50-350) t and a macroporosity of >=65%, assuming a material bulk density typical of non-primitive meteorite materials. A high degree of macroporosity suggests 2011 MD to be a rubble-pile asteroid, the rotation of which is more likely to be retrograde than prograde.