Session 42 - Solar Systems.
Display session, Tuesday, January 16
North Banquet Hall, Convention Center

## [42.18] An HST Archival Search for Small Satellites of Pluto

B. C. Flynn, S. A. Stern (SwRI), J. W. Parker (GSFC), J. C. Snowdall (U. Colorado)

Monte Carlo orbital stability calculations show that satellites with radii of \sim10s of km (assuming \rho=2.0 g cm^-3) can reside in stable orbits ranging from Pluto's Roche limit at 0.2a_0 to 0.47a_0, and beyond Charon's orbit from 2a_0 to the solar-tidal stability limit at \simeq100a_0, where a_0 is the Pluto-Charon separation distance (Stern et al., 1994). Satellite orbits are found to be unstable within a band around Charon's orbit ranging from 0.47a_0 to 2a_0.

A groundbased search for satellites beyond Charon's orbit resulted in an observational constraint on satellite size of \sim25 km radius beyond 10a_0 (Stern et al., 1991). With the launch of HST, it became possible to make a much more sensitive search of the satellite stability zones. Stern et al.\ (1994) have conducted an initial search of HST archival imaging data using 14 WFPC images of Pluto and Charon obtained in 1991 (Null et al., 1993). This initial search resulted in satellite size upper limits of \sim140 km radius between Pluto and Charon, and \sim35 km radius beyond Charon's orbit.

We have completed our HST archival search using the remaining pre-COSTAR imaging dataset, consisting of 60 WFPC images (PI Buie, PIDs 3848, 5020) and 36 FOC images (PI Macchetto, PIDs 3036, 3059; PI Albrecht, PID 5150). Our analysis of these images also resulted in no detections of possible new satellites of Pluto. As such, we confirm the satellite size upper limits obtained previously by Stern et al.\ (1994). The increased resolution and sensitivity of the post-COSTAR HST could provide tighter constraints on satellite sizes, or possibly detect new satellites.

Null et al., Astron.\ J., 105, 2319, 1993; Stern et al., Icarus, 94, 246, 1991; Stern et al., Icarus, 108, 234, 1994.