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The size distribution of the hot classical belt: Streaming instability and more

Presentation #506.02 in the session Things that Figuratively “Go Bump in the Kuiper Belt, Chapter One”.

Published onOct 20, 2022
The size distribution of the hot classical belt: Streaming instability and more

Thanks to its exquisite calibration, OSSOS allows to precisely determine the size distribution of the classical Kuiper belt (non-resonant objects between 40 and 48 au) for objects in size range 100 to 500 km (absolute magnitude 5 to 9). This allows to connect to the MPC database derived size distribution for the largest objects (> 400 km) which is almost complete for these large objects (absolute magnitude ≲ 5.5). With the precise orbits from the OSSOS sample, we determined that the free inclination with respect to the improved local forced plane, as determined by Huang et al. (2022) cleanly separate the cold and hot (excited) populations in the classical belt, with a split around 4.5° in free inclination.

Using this definition of the cold and hot samples, we show that the size distribution of the hot population is parallel to that of the cold population in absolute magnitude H range 5.5 to 8.5 (see Figure 1, where the cold population has been multiplied by a factor of 2), hinting at a common formation mechanism in that range. The hot population being formed in a much denser environment (at least a factor of 100), the large number of big TNOs allows to initiate a second stage of planetesimal growth, such as runaway accretion or peeble accretion, which yields the flat size tail to large objects down to H ~ 0. At the small size end, the cratering records on Pluto/Charon and Arrokoth, as well as the comet sizes hint at an exponential H distribution with slope 0.4-0.5, similar for both populations. The resonant and scattering populations exhibit a feature around H ~ 8.5, possibly due to collisional evolution in a rather dense environment. This feature, if present, is not visible in the current classical belt sample due to lack of depth.

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