The orbital distribution of trans-Neptunian objects (TNOs) in the distant Kuiper Belt (with semimajor axes beyond the 2:1 resonance, roughly a = 50–100 au) provides constraints on the dynamical history of the outer solar system. Recent studies show two striking features of this region: (1) a very large population of objects in distant mean-motion resonances with Neptune, and (2) the existence of a substantial detached population (nonresonant objects largely decoupled from Neptune). Neptune migration models are able to implant some resonant and detached objects during the planet migration era, but many fail to match a variety of aspects of the orbital distribution. In this work, we report simulations carried out using an improved version of the GPU-based code GLISSE, following 100,000 test particles per simulation in parallel while handling their planetary close encounters. We demonstrate for the first time that a 2 Earth-mass rogue planet temporarily present during planet formation can abundantly populate both the distant resonances and the detached populations, surprisingly even without planetary migration. We show how weak encounters with the rogue planet greatly increase the efficiency of filling the resonances, while also dislodging TNOs out of resonance once they reach high perihelia. The rogue’s secular gravitational influence simultaneously generates numerous detached objects observed at all semimajor axes. These results suggest that the early presence of additional planet(s) reproduces the observed TNO orbital structure in the distant Kuiper Belt.

Using CFHT imaging data, we searched a 1.1 deg2 field on each side of Saturn down to magnitude m w ≃ 26.3, corresponding to diameters of D ≃ 3 km. We detected 120 objects, which were comoving with Saturn and are nearly certainly irregular moons. For example, all but one of our detections brighter than magnitude 25.5 link to known Saturnian irregulars, with 40 linkages that thus extend the orbital arc of previous discoveries. Extrapolating our sample's characterized detections (those for which we can debias the search) to the entire Saturnian irregular population, we estimate that there are 150 ± 30 moons down to D = 2.8 km, which is approximately three times as many irregular moons as Jupiter down to the same size. At the smallest sizes, from D = 3.8 down to 2.8 km, we find that the Saturnian irregular population exhibits a steep size distribution of the differential power-law index q = 4.9 − 0.6 + 0.7 . We believe this steep size distribution is the signature of a relatively recent (few hundred Myr ago) collisional event in Saturn's retrograde irregular population.

We have searched a 2010 archival data set from the Canada–France–Hawaii Telescope for very small (km-scale) irregular moons of Jupiter in order to constrain the size distribution of these moons down to radii of ∼400 m, discovering 52 objects that are moving with Jupiter-like on-sky rates and are nearly certainly irregular moons. The four brightest detections, and seven in total, were all then linked to known Jovian moons. Extrapolating our characterized detections (those down to magnitude m r  = 25.7) to the entire retrograde circum-Jovian population, we estimate the population of radius >0.4 km moons to be 600 (within a factor of 2). At the faintest magnitudes, we find a relatively shallow luminosity function of exponential index α = 0.29 ± 0.15, corresponding to a differential diameter power law of index q ≃ 2.5.

We present a tracked orbit for a recently discovered 25th magnitude irregular moon of Saturn, using Canada-France-Hawaii Telescope imaging. Our 2 yr of observational arc on the moon leads to an orbit with a semimajor axis of 11.2 million kilometers and an inclination of 44 deg. This makes it one of the smallest Saturnian irregular moon orbits known and puts the moon in the Inuit group. This moon is also a magnitude brighter than the faintest known Saturnian irregulars. We show that the moon’s small semimajor axis results in it spending most of the time lost in the glare of the often-nearby planet, thus explaining how it escaped detection in previous surveys. We postulate that the disparity in the known inventory with more retrograde than direct irregular moons is partly due to the selection bias against finding the direct moons (whose groupings have smaller semimajor axis).

<p>We have searched a 2010 archival data set from the Canada-France-Hawaii Telescope for very small (km-scale) irregular moons of Jupiter in order to constrain the size distribution of these moons down to radii of ~400m, discovering 53 objects which are moving with Jupiter-like on-sky rates and are nearly certainly irregular moons. The four brightest detections, and seven in total, were all then linked to known jovian moons. Extrapolating our characterized detections (those down to magnitude m<sub>r</sub>=25.7) to the entire retrograde circum-jovian population, we estimate the population of radius > 0.4km moons to be 600 (within a factor of 2).  At the faintest magnitudes we find a relatively shallow luminosity function of exponential index α = 0.29 ± 0.15, corresponding to a differential diameter power law of index q ≈ 2.5.</p>