A Tenuous Cloud of Neutrals In the Outer Solar System from KBOs

Several studies have estimated escape rates, ionization/ dissociation rates, and initial velocities of gasses escaping Pluto's atmosphere. Although the estimated escape rate of Nitrogen has been greatly reduced after the New Horizons encounter, it is possible that the escape rate could have been much higher in the past. In this study, we focus on escaping nitrogen, methane, and hydrogen from Pluto. We also extend our modeling to include Eris, Makemake, 2007 OR10, Quaoar, and Varuna. These Kuiper Belt Objects (KBOs) are all >500 km in radius or recently underwent collisions and show evidence of escaping volatiles. A Monte-Carlo simulation is used to track the trajectories of each outgassed neutral from these KBOs. For each species, a tenuous neutral cloud forms that extends around the Sun for most of each orbit. We find that the maximum average local density is less than 0.1 m^-3 for H2 and CH4 and close to 10^-4 m^-3 for N2. If the N2 density is scaled up to pre-New Horizons encounter estimate, which could be applicable for other KBOs without HCN (or similar coolant) in their atmospheres, the density of N2 jumps to 1 m^-3. This suggests that any neutral cloud forming due to KBOs in the outer solar system would be extremely tenuous.