Kuiper Belt Objects (KBOs) are remnants of the swarm of primitive bodies that accreted in the outer parts of the protoplanetary nebula as the Solar System formed. They have diverse spectroscopic and dynamical properties, which may represent a coded memory of chemical and orbital processes early in the Solar System's history. Remarkably, 15% of KBOs are found orbiting about each other in binary or multiple systems. This provides a way to measure KBO masses and constrain their histories, as well as to test theories for the evolution of the protoplanetary disk. But first, the orbits themselves need to be determined. In this project, the collaborating team will carry out high-resolution imaging observations of KBO binaries, using the laser guide-star adaptive optics system on the Gemini-North telescope, roughly doubling the sample of known orbits. The observing program will obtain semi-major axes, eccentricities, periods, and spatial orientations for the orbits over the course of 3 years. From the data, constraints on object masses, shapes, and composition will be derived. The statistics of the orbital elements will constrain both the mode of binary formation and the subsequent evolution, which are tied to conditions in the protoplanetary nebula. In addition to the observational program, the proposing team will contribute to Lowell Observatory's middle-school outreach program for the Navajo and Hopi communities, and will supervise undergraduate students in research. Lowell's partnership in the Discovery Channel Telescope project will also contribute to broader public understanding of astronomy.

Project Report

This project has been using high spatial resolution imaging observations of Kuiper belt binaries to determine their mutual orbits. The mutual orbits of these systems provide their masses, a fundamental physical property at the core of more detailed analyses. System masses can be combined with stellar occultation sizes or with radiometric size estimates from Spitzer, Herschel, and eventually ALMA and JWST to compute bulk densities, a key constraint on bulk composition. Mutual orbital parameters also provide telling clues about both the protoplanetary disk environment in which these binaries formed and the subsequent dramatic evolution of the outer Solar System that turned the quiescent planetesimal disk into today's highly excited and depleted remnant belt. We have obtained orbits and masses for several new systems and have contributed to publication of several papers, with others still in progress. Among our results, we discovered two systems (79360 Sila-Nunam and 385446 Manwe-Thorondor) that are doing mutual events, like Pluto and Charon did during the mid-1980s, presenting opportunities to characterize those systems in greater detail that are being pursued by several groups. A graduate student (now graduated) was involved in the work doing observations as well as dynamical models of the evolution of binary systems. The project ends 2015 June 30.

National Science Foundation (NSF)
Division of Astronomical Sciences (AST)
Application #
Program Officer
Maria Womack
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
Lowell Observatory
United States
Zip Code