The Moons of Kuiper Belt Dwarf Planets Makemake and 2007 OR10

The first science goal is to determine the density of both of the members of each system, via estimates of their mass and mean radius based on HST observations. We will then explore a suite of different chemical models for the composition of ice and rock inside each object to determine the ice/rock ratio for each member of the Makemake and 2007 OR10 system. As estimates of the sizes and masses of the objects are refined through subsequent observations, we will adjust our models accordingly.

The second science goal is to determine the type of collision that could have formed the Makemake and 2007 OR10 systems. This will be accomplished using hydrocode simulations of the collisions between two ice/rock bodies. The total mass of impacting material is equal to the total mass of the final system. The angular momentum contained in the collision is assumed to be equal to the final system angular momentum. We will explore impact scenarios with different geometries and impact velocities. Our choices of conditions will be guided by prior studies of Kuiper Belt Object origins and collisions (e.g., Canup 2005, Leinhardt et al., 2010, Canup 2011, Kenyon & Bromley 2013, Desch 2015). To simulate the impacts, we will use the open‐source hydrocode Spheral++ (Owen et al., 1998), coupled with the ANEOS equation of state (Thompson & Lauson 1972) for dunite (Canup, Barr & Crawford 2013) and water ice (Turtle & Pierazzo 2001). We will explore both differentiated impactors/targets (i.e., a fully consolidated rock core) and undifferentiated/partially differentiated objects. The outcome of each impact simulation will be analyzed to determine the mass, radius, composition, and spin state of the primary body, as well as the mass, radius, orbit, composition, and spin state of the final moon (or moons) that form. Impacts that yield properties close to the Makemake or 2007 OR10 systems will be considered successful. This will shed light on the eccentricity/inclination distribution in the early Kuiper Belt, as well as the differentiation state of the precursor objects, which can shed light on their mode of origin.

In Year 1 of the effort, we will focus on determine masses and radii for the objects, as well as determining their ice/rock ratios. We will also begin hydrocode modeling, which will continue through Year 2.

The start date for salary is October 1, 2017 and continues through September 20, 2019. No travel funds are requested for the duration of the grant.

PI Barr is solely responsible for the completion of all tasks described in this budget.

Calculations of the densities and ice/rock ratios in Year 1 of the project will be performed using C programs written by the PI. Simulations of the formation of the Makemake and 2007 OR10 systems will be performed using Spheral++, which is a freely available, open‐source software package. The ANEOS equation of state is open‐source, but not freely available. However, we have previously obtained a copy of the package and have permission use it for the purposes described here.