We conducted an extensive search for dust or debris rings in the Pluto-Charon system before , during , and after the New Horizons encounter in July 2015 .
Methodologies included attempting to detect features by back-scattered light during the approach to Pluto ( phase angle \alpha \sim 15 ^ { \circ } ) , in situ detection of impacting particles , a search for stellar occultations near the time of closest approach , and by forward-scattered light imaging during departure ( \alpha \sim 165 ^ { \circ } ) .
An extensive search using the Hubble Space Telescope ( HST ) prior to the encounter also contributed to the final ring limits .
No rings , debris , or dust features were observed , but our new detection limits provide a substantially improved picture of the environment throughout the Pluto-Charon system .
Searches for rings in back-scattered light were covered the range 35,000–250,000 km from the system barycenter , a zone that starts interior to the orbit of Styx , the innermost minor satellite , and extends out to four times the orbital radius of Hydra , the outermost known satellite .
We obtained our firmest limits using data from the New Horizons LORRI camera in the inner half of this region .
Our limits on the normal I / F of an unseen ring depends on the radial scale of the rings : 2 \times 10 ^ { -8 } ( 3 \sigma ) for 1500 km wide rings , 1 \times 10 ^ { -8 } for 6000 km rings , and 7 \times 10 ^ { -9 } for 12,000 km rings .
Beyond \sim 100 , 000 km from Pluto , HST observations limit normal I / F to \sim 8 \times 10 ^ { -8 } .
Searches for dust features from forward-scattered light extended from the surface of Pluto to the Pluto-Charon Hill sphere ( r _ { Hill } = 6.4 \times 10 ^ { 6 } km ) .
No evidence for rings or dust clouds was detected to normal I / F limits of \sim 8.9 \times 10 ^ { -7 } on \sim 10 ^ { 4 } km scales .
Four stellar occulation observations also probed the space interior to Hydra , but again no dust or debris was detected .
The Student Dust Counter detected one particle impact 3.6 \times 10 ^ { 6 } km from Pluto , but this is consistent with the interplanetary space environment established during the cruise of New Horizons .
Elsewhere in the solar system , small moons commonly share their orbits with faint dust rings .
Our results support recent dynamical studies suggesting that small grains are quickly lost from the Pluto-Charon system due to solar radiation pressure , whereas larger particles are orbitally unstable due to ongoing perturbations by the known moons .