The densities of mid-sized Kuiper belt objects are a key constraint into
understanding the assembly of objects in the outer solar system. These objects
are critical for understanding the currently unexplained transition from the
smallest Kuiper belt objects with densities lower than that of water to the
largest objects with significant rock content. Mapping this transition is made
difficult by the uncertainties in the diameters of these objects, which maps
into an even larger uncertainty in volume and thus density. The substantial
collecting area of the Atacama Large Millimeter Array allows significantly more
precise measurements of thermal emission from outer solar system objects and
could potentially greatly improve the density measurements. Here we use new
thermal observations of four objects with satellites to explore the
improvements possible with millimeter data. We find that effects due to
effective emissivity at millimeter wavelengths make it difficult to use the
millimeter data directly to find diameters and thus volumes for these bodies.
In addition, we find that when including the effects of model uncertainty, the
true uncertainties on the sizes of outer solar system objects measured with
radiometry are likely larger than those previously published. Substantial
improvement in object sizes will likely require precise occultation
measurements.Comment: AJ, in pres
