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Colors of Cold Classical KBOs from the HST Solar System Origins Legacy Survey (SSOLOS)

Presentation #202.03 in the session TNO Theory and Physical Properties (Oral Presentation)

Published onOct 23, 2023
Colors of Cold Classical KBOs from the HST Solar System Origins Legacy Survey (SSOLOS)

The dynamically distinct Cold Classical (CC) Kuiper Belt is a reservoir of small bodies that both observations and modeling identify as an in-situ primordial population. During HST Cycle 26 a legacy survey was executed to collect F606W and F814W filter photometry on a sample of 197 of these CCs (Hr<8) based on their discovery in the carefully designed and fully calibrated Outer Solar System Survey. The images were analyzed for binarity and measured photometrically using a Tiny Tim matching algorithm. We report on the final color results of this survey which found 25 of 197 objects to be well resolved (≥0.05”) binaries yielding a binary fraction at face value of 13%; including partially resolved objects the fraction is closer to 20%. For resolved binaries there is a concentration of components with similar color consistent with previous studies, but no longer a perfect correlation. The binary systems are, on average, one magnitude brighter then solitary objects, but the blended binaries span the magnitude space between the two populations suggesting a continuum of sorts from bright to faint. We interpret that whatever is going on with color vs. size is really about size at formation, and not due to fragments of collisions being redder because we see that smaller objects appear redder in both the solitary and binary color results. Observations of Arrokoth’s lobes by New Horizons also support this conclusion that binary components are related to formation mechanism and environment, not due to shattering by collisions. Support for this program was provided by NASA through a grant from STScI, which is operated by the AURA, Inc., under NASA contract NAS 5-26555.

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