Limits on Pluto’s ring system from the June 12 2006 stellar occultation and implications for the New Horizons impact hazard

Abstract

The Pluto system passed in front of a 15th magnitude star on 12 Jun 2006.We observed this occultation from the 3.9 m Anglo-Australian Telescope (AAT), and took photometric observations every 100 msec for three hours. Our threehour baseline of data provides among the longest and highest-quality occultation dataset of the Pluto system ever taken. Results on Pluto's atmospheric structure from these data have been previously reported (Young et al. 2008). Here we report on limits for rings, ring arcs, and small satellites within the system. We find a 3σ upper limit on the normal optical depth of τ < 0.07 for narrow rings of width 2.4 km, and τ < 5 × 10 −3 for rings of width 1500 km. We also detect no discrete objects of radius 220 m or larger along the occultation path. Motivated by the upcoming flyby of New Horizons through the Pluto system, we estimate the dust impact hazard to the spacecraft based on our optical depth limits and those derived from imaging with the Hubble Space Telescope.

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

“…We verified the upper limits on the ring optical depth derived in the previous section using an analytic approach. We looked for statistically significant outliers in the dataset at various spatial resolutions, following a similar technique used by Throop et al (2015) to search for rings around Pluto during the New Horizons flyby. 1).…”

Rings Beyond the Giant Planets

“…Boissel et al (2014) conducted one such search, setting an upper limit of 30-100 m for the equivalent depth of a narrow ring (see Chapter 4 for the formal definition of "equivalent depth," a form of radially-integrated optical depth). Similarly, Throop et al (2015) set a limit of ∼ 170 m assuming a nominal ring of width 2.4 km.…”

A Pluto–Charon Sonata: The Dynamical Architecture of the Circumbinary Satellite System

“…Over the past few decades, various groups have observed Pluto and Charon occult fairly bright stars to infer the extent and physical properties of their atmospheres and to plan for the New Horizons flyby (e.g., Person et al 2006;Sicardy et al 2011;Person et al 2013;Throop et al 2015;Gulbis et al 2015;Bosh et al 2015;Dias-Oliveira et al 2015;Sicardy et al 2016;Pasachoff et al 2016, 2017, andreferences therein). With exposure times of 0.25 to 5 sec on 1-m to 2.5-m telescopes, the typical signal-to-noise ranges from roughly 10 to better than 100.…”

“…The calculations of massless tracers orbiting between Styx and Hydra also provide new insights into the lack of emission from small particles detected from New Horizons data (Lauer et al 2018). Prior to the New Horizons flyby, several studies derived upper limits on small moons and dust emission from direct imaging (e.g., Steffl et al 2006;Marton et al 2015) and occultations (Boissel et al 2014;Throop et al 2015). Theoretical studies based on n-body simulations predicted steady-state optical depths from a balance between dust production from impacts on Pluto-Charon and the smaller satellites and losses from radiation pressure and dynamical ejections (Stern et al 2006;Pires Dos Santos et al 2011;Poppe & Horányi 2011;Pires dos Santos et al 2013).…”