New constraint on the atmosphere of (50000) Quaoar from a stellar occultation

TL;DR

This study used stellar occultation data to set new upper limits on Quaoar's surface methane atmosphere, indicating it is likely absent or extremely thin.

Contribution

First high-cadence occultation observation of Quaoar that constrains its atmospheric pressure limits below previous expectations.

Findings

No detectable atmospheric refraction observed.

Upper limit of 6 nbar for surface pressure at 1σ confidence.

Absence of a significant methane atmosphere on Quaoar.

Abstract

We report observations of a stellar occultation by the classical Kuiper belt object (50000) Quaoar occurred on 28 June 2019. A single-chord high-cadence (2 Hz) photometry dataset was obtained with the Tomo-e Gozen CMOS camera mounted on the 1.05 m Schmidt telescope at Kiso Observatory. The obtained ingress and egress data do not show any indication of atmospheric refraction and allow to set new $1\sigma$ and $3\sigma$ upper limits of 6 and 16 nbar, respectively, for the surface pressure of a pure methane atmosphere. These upper limits are lower than the saturation vapor pressure of methane at Quaoar's expected mean surface temperature ($T \sim 44$ K) and imply the absence of a $\sim$10 nbar-level global atmosphere formed by methane ice on Quaoar's surface.