The Compiled Size Frequency Distribution of Kuiper Belt Objects

The Size Frequency Distribution (SFD) of Kuiper Belt Objects (KBOs) has long been used to infer the formative history of these objects. Telescopic surveys have revealed an SFD remarkably consistent in overall shape with predictions from models of formation through streaming-instability and pebble cloud collapse (SI+PC) [1,2,3]. Inference of the populations too small (too faint) for direct telescopic detection is possible from the crater SFD on Pluto-Charon as seen by New Horizons [4], and the SFD of the Jupiter Family comets (JFCs) [5] which originate from the excited KBO population. Inference of the SFD from each of these indirect observations presents additional challenges, notably the assumed impactor scaling law and the difficulty in debiasing the observed JFC population. The Jupiter Trojans provide additional inference, as they are predicted to share a common primordial origin with the dynamically excited KBOs [6]. In Figure 1. We compile KBO SFD data from observational surveys, including ground and space-based surveys, the Pluto-Charon cratering record, and the SFD inferred from the JFCs. We also include Jupiter Trojan SFD data [7,8]. All KBO SFD data are in strong agreement when scaled to a common albedo and offset for relative on-sky densities and production functions. Notable conclusions are:

• Both the dynamically excited and cold KBO SFDs are consistent with expectations of SI+PC over most of the observable range, turning over to a shallower slope only at small object sizes (D~2 km).
• The JFC and cratering SFDs prove remarkably consistent, showing that the turnover is an intrinsic property of the KBO population and not due to cometary mass loss or assumed crater scaling laws.
• As the cold classical population comprises much of the Pluto-Charon, the turnover appears to be a primordial feature common to both the dynamically cold and excited populations.
• The differences exhibited of the Trojans for D<10 km are likely collisionally driven.

 

Figure 1: The compiled cumulative KBO SFD, renormalized by radius squared, akin to an R-plot. Black dashed lines are data drawn from the Pluto-Charon cratering record seen from New Horizons. The blue data are telescopic data (CLASSY: dark, JFCs: light) and the OSSOS limits are traced in light black. The slope inferred from the JWST Pencilbeam is shown in red. Trojan data are shown in magenta. The yellow curve shows the best-fit exponential taper which matches expectations from SI+PC simulations. 

 

References

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