OSSOS. VIII. The Transition between Two Size Distribution Slopes in the Scattering Disk

Abstract

The scattering trans-Neptunian Objects (TNOs) can be measured to smaller sizes than any other distant small-body population. We use the largest sample yet obtained, 68 discoveries, primarily by the Outer Solar System Origins Survey (OSSOS), to constrain the slope of its luminosity distribution, with sensitivity to much fainter absolute H-magnitudes than previous work. Using the analysis technique in Shankman et al., we confirm that a single slope for the H-distribution is not an accurate representation of the scattering TNOs and Centaurs, and that a break in the distribution is required, in support of previous conclusions. A bright-end slope of α b =0.9 transitioning to a faintend slope α f of 0.4-0.5 with a differential number contrast c from 1 (a knee) to 10 (a divot) provides an acceptable match to our data. We find that break magnitudes H b of 7.7 and 8.3, values both previously suggested for dynamically hot Kuiper Belt populations, are equally non-rejectable for a range of α f and c in our statistical analysis. Our preferred divot H-distribution transitions to α f =0.5 with a divot of contrast c=3 at H b =8.3, while our preferred knee H-distribution transitions to α f =0.4 at H b =7.7. The intrinsic population of scattering TNOs required to match the OSSOS detections is 3×10 6 for H r <12, and 9×10 4 for H r <8.66 (D100 km), with Centaurs having an intrinsic population two orders of magnitude smaller.

Trans-Neptunian Objects Transiently Stuck in Neptune’s Mean-motion Resonances: Numerical Simulations of the Current Population

“…Our initial conditions for the simulations consist of 8500 TNO particles; only particles whose semimajor axes changed by 1.5au or more within the last 10Myr of the Kaib et al (2011) model run are included, as this is how the observed actively scattering TNO population is defined. Shankman et al (2016) and Lawler et al (2018) found that these initial conditions provide an adequate representation of the population of scattering TNOs observed by the Canada France Ecliptic Plane Survey (CFEPS; Petit et al 2011), the Outer Solar System Origins Survey (OSSOS; Bannister et al 2016bBannister et al , 2018, and Alexandersen et al (2016). We numerically integrate the orbits of the model scattering population as massless test particles using the rmvs3 routine in SWIFT (Levison & Duncan 1994) with the Sun and the four giant planets included as massive bodies.…”

“…To generate these predictions, we use the constraints on the scattering population from OSSOS (Bannister et al 2016b(Bannister et al , 2018. Based on the number of scattering objects detected in this survey, Lawler et al (2018) estimated that there are 1.1± 0.2×10 4 scattering objects with H r <8.66 and semimajor axes in the range 30-100 au. Producing this estimate relies on assuming a model for the true orbital and H-magnitude distribution of the scattering population.…”

“…Producing this estimate relies on assuming a model for the true orbital and H-magnitude distribution of the scattering population. Lawler et al (2018) used the same Kaib et al (2011) orbital model, modified as in Shankman et al (2013) to account for the larger orbital inclinations in the observed population compared to the model. This is the same orbital distribution we take as our simulation initial conditions (Section 2.1), so the Lawler et al (2018) scattering population estimate will produce self-consistent predictions for our resonant populations.…”

“…Lawler et al (2018) used the same Kaib et al (2011) orbital model, modified as in Shankman et al (2013) to account for the larger orbital inclinations in the observed population compared to the model. This is the same orbital distribution we take as our simulation initial conditions (Section 2.1), so the Lawler et al (2018) scattering population estimate will produce self-consistent predictions for our resonant populations. The population estimate above is for a divot model of the H-magnitude distribution, but because we use an H-magnitude cut H r < 8.66, the scattering population estimate is not very sensitive to this choice of a divot instead of a knee in the H-magnitude distribution (see Table 1 in Lawler et al 2018, where the difference in the total scattering population with H r <8.66 for a divot versus a knee is only ∼10%, smaller than the population uncertainty).…”

“…For each individual resonance, the stuck population in that resonance then represents f r ×0.676 of the scattering population. We have translated the predicted fraction of resonant objects to an actual number of objects based on the Lawler et al (2018) estimate that there are (1.1±0.2)×10 4 actively scattering objects with 30au <1<100 au based on the results of OSSOS  (Bannister et al 2016b(Bannister et al , 2018; all predictions should be assumed to have an uncertainty of ∼20% due to the observational uncertainty on the scattering population estimate. We list only resonances of note here.…”