Table 1.

Input parameters used to determine the upper limit for fractionation due to escape based on published studies of Pluto. Column density is presumed to be in steady state while the rates for sublimation, escape and photochemistry evolve with time according to Ribas et al. (2005). The total fractionation is constant with time.

	Variable	Jeans escape	Hydrodynamic escape
Atmospheric column density (cm−2)	n	3 × 1021	3 × 1021
Nitrogen abundance	X	0.996	0.996
Escape rate (cm−2 s−1)	ϕe	7 × 109 a	1.8 × 1010 b
Escape fractionation	fe	0.739 c	0.983
Photochemical loss rate (cm−2 s−1)	ϕc	2.3 × 107 d	2.3 × 107 d
Photochemical fractionation	fc	2.6 e	2.6 e
Total loss fractionation	floss	0.822	0.983
Maximum R/R0	R/R0	8.54	1.23
Most likely R/R0	R/R0	1.35	1.05

^aTucker et al., 2012;

^bKrasnopolsky, 1999; Tian and Toon 2005; Strobel 2008;

^cAssuming λ=5.4 from Tucker et al., 2012, which provides maximum Jeans escape fractionation;

^dKrasnopolsky and Cruikshank, 1999;

^eBased on f_c determined for Titan by Mandt et al., 2009.