Microwave Emission from the Edgeworth-Kuiper Belt and the Asteroid Belt Constrained from WMAP

TL;DR

This study uses WMAP data to constrain the microwave emission from the Edgeworth-Kuiper and asteroid belts, limiting their total mass and size distribution, and highlights the need for more sensitive future observations.

Contribution

It provides the first constraints on belt object populations from CMB anisotropy data, linking microwave emission limits to size distribution models.

Findings

Total mass of Edgeworth-Kuiper belt objects < 0.2 Earth masses

Size distribution index q ~ 3.5 for small objects in Kuiper belt

Grain population in asteroid belt should not have q > 3.6

Abstract

Objects in the Edgeworth-Kuiper belt and the main asteroid belt should emit microwaves that may give rise to extra anisotropy signals in the multipole of the cosmic microwave background (CMB) experiment. Constraints are derived from the absence of positive detection of such anisotropies for ell < 50, giving the total mass of Edgeworth-Kuiper belt objects to be smaller than 0.2 earth mass. This limit is consistent with the mass extrapolated from the observable population with the size of a > 15 km, assuming that the small-object population follows the power law in size dN/da ~ a^{-q} with the canonical index expected for collisional equilibrium, q ~ 3.5, with which 23% of the mass is ascribed to objects smaller than are observationally accessible down to grains. A similar argument applied to the main asteroid belt indicates that the grain population should not increase faster than q ~ 3.6 towards smaller radii, if it follows the power law continued to observed asteroids with larger radii. It is underlined that both cases are at or only slightly above the limit that can be physically significant, implying the importance of tightening further the CMB anisotropy limit, which may be attained with the observation at higher radio frequencies.