Constraints on Quaoar’s Rings and Atmosphere from JWST/NIRCam Observations of a Stellar Occultation

Abstract

Observations of stellar occultations have revealed that small bodies are capable of hosting ring systems. The trans-Neptunian object Quaoar is the host of an enigmatic ring system, with two rings located well outside the Roche limit. To better understand these structures, we observed a stellar occultation by Quaoar and its rings using the James Webb Space Telescope’s NIRCam instrument. Our observations detect both known rings, although Q2R—the inner known ring—is not detected on both sides of Quaoar, showing that it has substantial azimuthal variations similar to Q1R, the outer ring. We also fit a model of the ring radii and pole orientation of the ring system, which confirms that Quaoar’s spin–orbit and Weywot’s mean-motion resonances (especially Weywot’s 6:1) may play a role in the rings’ confinement and stability. In addition to examination of Quaoar’s ring system, we also use our observations to place upper limits on a putative CH _4 atmosphere around Quaoar, finding that no global atmosphere with surface pressure > 1 nbar can exist (at 3 σ significance). The lack of atmosphere supports the hypothesis that atmospheric processes are not the source of Quaoar’s recently discovered inventory of light hydrocarbons.

Keywords

• Planetary rings
• Stellar occultation
• Trans-Neptunian objects
• James Webb Space Telescope