R. E. Johnson^1,2, A. Oza^3,4, L. A. Young⁵, A. N. Volkov⁶, and C. Schmidt^1,3
1Engineering Physics, University of Virginia, Charlottesville, VA 22904, USA
²Physics, New York University, New York, NY 10003, USA
³Department of Astronomy, University of Virginia, Charlottesville, VA 22904, USA
⁴CNRS, LATMOS/IPSL, Université Pierre et Marie Curie, Paris, France
⁵SwRI, 1050 Walnut Street, Boulder, CO 80302-5150, USA
⁶Department of Mechanical Engineering, University of Alabama, Tuscaloosa, AL 35487, USA

Observations indicate that some of the largest Kuiper Belt Objects (KBOs) have retained volatiles in the gas phase (e.g., Pluto), while others have surface volatiles that might support a seasonal atmosphere (e.g., Eris). Since the presence of an atmosphere can affect their reflectance spectra and thermal balance, Schaller & Brown examined the role of volatile escape driven by solar heating of the surface. Guided by recent simulations, we estimate the loss of primordial N2 for several large KBOs, accounting for escape driven by UV/EUV heating of the upper atmosphere as well as by solar heating of the surface. For the latter we present new simulations and for the former we scale recent detailed simulations of escape from Pluto using the energy limited escape model validated recently by molecular kinetic simulations. Unlike what has been assumed to date, we show that unless the N2 atmosphere is thin (<~10¹⁸ N2 cm^-2) and/or the radius small (<~200–300 km), escape is primarily driven by the UV/EUV radiation absorbed in the upper atmosphere. This affects the discussion of the relationship between atmospheric loss and the observed surface properties for a number of the KBOs examined. Our long-term goal is to connect detailed atmospheric loss simulations with a model for volatile transport for individual KBOs.

Reference
Johnson RE, Oza A, Young LA, Volkov AN and Schmidt C (2015) Volatile loss and classification of Kuiper belt objects. Astrophysical Journal 809:43.
Link to Article [doi:10.1088/0004-637X/809/1/43]