Atmospheric escape explains diverse surface compositions of Pluto vs Sedna

Kuiper Belt Objects are thought to be remnants of early solar system materials, which have retained volatiles such as CH 4 and C 2 H 6 . Spectroscopic data from various sources reveals that while Pluto retains CH 4 and C 2 H 6 , Sedna shows a lack of CH 4 but an abundance of C 2 H 6 (Emery et al. 2024). We hypothesized that CH 4 , while stable on Pluto, is able to escape from less massive Sedna sufficiently rapidly to be depleted over the age of the solar system, while C 2 H 6 has been retained due to its larger molecular mass. Utilizing models for Jeans escape and hydrodynamic escape, as appropriate for a given mass of object and of escaping species, we analyzed the stability and escape rates of CH 4 and C 2 H 6 on both Pluto and Sedna. We explored a wide range of masses of Sedna, ranging from ½ to ⅒ the mass of Pluto, and three different abundances of CH 4 and C 2 H 6 using measured values from Comet 67-P, and Enceladus, and an upper limit assuming clathrate hydrate. We find that CH 4 remains stable on Pluto, but escapes from Sedna due to its lower mass, whereas C 2 H 6 remains stable when using both 100 % and 10 % outgassing rates. This result is in agreement with the observed spectra and leads to a tighter mass constraint for Sedna. Our model also explains the observed absence of methane on another KBO, Gonggong. • Simple escape models can explain the difference in observed volatile abundances on Pluto vs. Sedna. • Such models allow the constraints on the mass of Sedna to be tightened. • The model also explains Gonggong's surface volatiles