Probing the Hill Sphere of (486958) 2014 MU$_{69}$: HST FGS Observations During the July 17, 2017 Stellar Occultation

TL;DR

This study used HST FGS observations during a stellar occultation to investigate the environment around Kuiper Belt Object 2014 MU69, setting upper limits on rings or debris within its Hill sphere.

Contribution

First to use HST FGS for high-resolution photometry to constrain dust and ring opacity around a Kuiper Belt Object during a stellar occultation.

Findings

No rings or debris detected within 75,000 km of MU69.

Set upper limits on dust opacity in the Hill sphere.

Provided calibration and reduction methods for FGS photometry.

Abstract

We observed the July 17, 2017 stellar occultation of HD 168233 by the Kuiper Belt Object (486958) 2014 MU$_{69}$, the close flyby target of the extended New Horizons mission. Rather than capture a solid body occultation by the KBO itself, our program aimed to constrain the opacity of rings, moons, or other debris in the nearby environment. We used the Hubble Space Telescope Fine Guidance Sensors (HST FGS) instrument in TRANS F583W mode to collect 40 Hz time resolution photometry of the stellar occultation star for two HST orbits during this observation. We present the results of reduction and calibration of the HST FGS photometry, and set upper limits on rings or other dust opacity within the Hill sphere of (486958) 2014 MU$_{69}$ at distances ranging from $\sim$20,000 km to $\sim$75,000 km from the main body.