WUNA Lunch Talk:

Anne Verbiscer

University of Virginia

Sila-Nunam: An Eclipsing Binary in the Kuiper Belt

September 26

12:10PM, Room 230, NRAO, Edgemont Road


Like most known transneptunian binaries, (79360) Sila-Nunam is a member of the "Classical" sub-population of transneptunian objects (TNOs) which orbit the Sun on relatively low-inclination, low-eccentricity orbits not in mean-motion resonance with Neptune. Classical TNOs are further subdivided into dynamically "hot" and "cold" subgroups, based on the inclinations of their heliocentric orbits. Binaries comprise approximately one-third of the low-inclination "Cold Classical" population and are of particular interest because they likely formed in situ beyond Neptune, perhaps near their present day locations with semi-major axes between 42 and 47 AU.

Sila-Nunam is currently undergoing mutual events in which the two components alternate in eclipsing and occulting each other as seen from Earth. The low eccentricity of the orbit and coincidence of the system's photometric lightcurve and orbital period are consistent with a system that is tidally locked and synchronized like that of Pluto-Charon. Mutual events of tidally-locked, synchronous binaries provide rich opportunities to learn about sizes, colors, shapes, and albedo patterns of the system components. Our current knowledge of albedo patterns on Pluto-Charon derives from observations of their mutual events between 1985 and 1990. The duration of the mutual event season depends on the size and separation of the bodies. Using sizes determined from thermal observations, the mutual event season for Sila-Nunam should last about a decade; however, the deepest, most central events will likely be observable in the 2013 apparition, with progressively shallower events thereafter for the next 4-5 years. I will present observations of two mutual events in the 2012 apparition in addition to the rotation and solar phase curves of Sila-Nunam. Successful observations of multiple mutual events of Sila and Nunam will ultimately characterize in detail one of the most pristine, unaltered bodies in the Solar System which has likely remained where it formed in the outermost region of the nebular disk.