Separate Lightcurves of Pluto and Charon

Abstract

We present new Hubble Space Telescope observations of the Pluto-Charon system taken with WFPC1 (PC6) between 1992 May 21 and 1993 August 18. Our observations consist of 52 images with the F555W filter and 8 images in the F439W filter. From these data we extracted individual lightcurves, phase coefficients, and colors for Pluto and Charon. These lightcurves have peak-to-peak variations of 0.33 and 0.08 mag, respectively. The lightcurve for Charon is consistent with its suspected synchronous rotation about Pluto. The linear phase coefficients are 0.0294 ± 0.0011 mag/deg for Pluto and 0.0866 ± 0.0078 mag/deg for Charon, spanning a range of phase angles from 0.6° to 2.0°. Charon's lightcurve has far less structure than Pluto's with minimum light corresponding to the anti-Pluto hemisphere. We found theB-Vcolor of Charon to be 0.710 ± 0.011 mag. Combined with previous mutual event measurements, the color of Charon is seen to be globally uniform. We also confirmed a reddishB-Vcolor for Pluto of 0.873 ± 0.002 and 0.862 ± 0.002 mag at 123° and 289° east longitude, respectively. These colors are consistent with prior mutual event observations but the higher precision measurement indicates that the surface of Pluto is slightly redder near minimum light.