Correlated Colors of Cold Classical Binary KBOs from the HST Solar System Origins Legacy Survey

In HST Cycle 26 we successfully observed a treasury sample of 197 cold classical (CC) Kuiper Belt Objects (KBOs), The Solar System Origins Legacy Survey (SSOLS), at optical wavelengths to measure an F606W-F814W color and to look for binaries using the Wide Field Camera 3/UVIS (WFC3/UVIS). Our KBO sample draws on the highly successful, and bias-correctable, ground-based discovery surveys — the Canada France Ecliptic Plane Survey (CFEPS), and the Outer Solar System Origins Survey (OSSOS) — with the goal of better understanding the binarity and luminosity function of the intrinsic CC KBO population. Here we give an overview of the survey and present the resolved colors for 25 clearly resolved binary cold classical KBOs, and the colors of 172 objects identified as solitary at the limit of HST’s spatial resolution. This large, high-quality sample permits robust testing of previously identified trends in colors. We find evidence supporting a trend of color with system brightness, with fainter objects in the sample being redder. Further, we find that while primaries and secondaries in binary systems have colors similar to one another, secondaries tend to be slightly redder than their primaries, and this shift is consistent with the overall trend of color with brightness in the entire CC KBO population. We will explore these trends and their implications for the origins and evolution for the CC KBO population and the outer solar system as a whole.