The Positions, Colors, and Photometric Variability of Pluto's Small Satellites from HST Observations 2005-2006

TL;DR

This study reports on HST observations of Pluto's small satellites P1 and P2, providing their positions, colors, and photometric stability, suggesting they are large, grey, and have low reflectivity.

Contribution

First detailed astrometric and photometric analysis of Pluto's small satellites using HST data from 2005-2006.

Findings

Both satellites are grey with neutral reflectivities.

No significant photometric variability observed.

Satellites likely larger with lower reflectivity than Charon.

Abstract

Pluto's two small satellites, temporarily designated S/2005 P 1 and S/2005 P 2, were observed on four dates (15.1 and 18.1 May 2005, 15.7 February 2006, and 2.8 March 2006) using the Hubble Space Telescope's (HST) Advanced Camera for Surveys (ACS). Here we collect together the astrometric positions of these two satellites (henceforth P1 and P2), as well as a single color measurement for each satellite and initial constraints on their photometric variability obtained during these observations. We find that both satellites have essentially neutral (grey) reflectivities, like Charon. We also find that neither satellite exhibited strong photometric variation, which might suggest that P1 and P2 are toward the large end of their allowable size range, and therefore may have far lower reflectivities than Charon.