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Title: The curiously warped mean plane of the Kuiper belt
Author: Kathryn Volk, Renu Malhotra

We measured the mean plane of the Kuiper belt as a function of semi-major axis. For the classical Kuiper belt as a whole (the non-resonant objects in the semi-major axis range 42-48 au), we find a mean plane of inclination i_m=1.8°^{+0.7°}_{-0.4°} and longitude of ascending node Omega_m=77°^{+18°}_{-14°} (in the J2000 ecliptic-equinox coordinate system), in accord with theoretical expectations of the secular effects of the known planets. With finer semi-major axis bins, we see evidence for the expected warp of the mean plane near semi-major axes 40-42 au, owed to the 18 nodal secular resonance. For the more distant Kuiper belt objects of semi-major axes in the range 50-80 au, the expected mean plane is close to the invariable plane of the solar system, but the measured mean plane deviates greatly from this: it has inclination i_m=9.1°^{+6.6°}_{-3.8°} and longitude of ascending node Omega_m=227°^{+18°}_{-44°}. We estimate this deviation from the expected mean plane to be statistically significant at the ~97-99% confidence level. We discuss several possible explanations for this deviation, including the possibility that a relatively close-in, low-mass unseen planet in the outer solar system is responsible for the warping.

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Kuiper Belt Kernel
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Title: Jumping Neptune Can Explain the Kuiper Belt Kernel
Author: David Nesvorny

The Kuiper belt is a population of icy bodies beyond the orbit of Neptune. A particularly puzzling and up-to-now unexplained feature of the Kuiper belt is the so-called `kernel', a concentration of orbits with semimajor axes a~44 AU, eccentricities e~0.05, and inclinations i<5 deg. Here we show that the Kuiper belt kernel can be explained if Neptune's otherwise smooth migration was interrupted by a discontinuous change of Neptune's semimajor axis when Neptune reached ~28 AU. Before the discontinuity happened, planetesimals located at ~40 AU were swept into Neptune's 2:1 resonance, and were carried with the migrating resonance outwards. The 2:1 resonance was at ~44 AU when Neptune reached ~28 AU. If Neptune's semimajor axis changed by fraction of AU at this point, perhaps because Neptune was scattered off of another planet, the 2:1 population would have been released at ~44 AU, and would remain there to this day. We show that the orbital distribution of bodies produced in this model provides a good match to the orbital properties of the kernel. If Neptune migration was conveniently slow after the jump, the sweeping 2:1 resonance would deplete the population of bodies at ~45-47 AU, thus contributing to the paucity of the low-inclination orbits in this region. Special provisions, probably related to inefficiencies in the accretional growth of sizable objects, are still needed to explain why only a few low-inclination bodies have been so far detected beyond ~47 AU.

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Kuiper Belt Objects
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Title: New Horizons: Long-Range Kuiper Belt Targets Observed by the Hubble Space Telescope
Author: Susan D. Benecchi1, Keith S. Noll, Harold A. Weaver, John R. Spencer, S. A. Stern, Marc W. Buie, Alex H. Parker

We report on Hubble Space Telescope (HST) observations of three Kuiper Belt Objects (KBOs), discovered in our dedicated ground-based search campaign, that are candidates for long-range observations from the New Horizons spacecraft: 2011 JY31, 2011 HZ102, and 2013 LU35. Astrometry with HST enables both current and future critical accuracy improvements for orbit precision, required for possible New Horizons observations, beyond what can be obtained from the ground. Photometric colors of all three objects are red, typical of the Cold Classical dynamical population within which they reside; they are also the faintest KBOs to have had their colors measured. None are observed to be binary with HST above separations of ~0.02 arcsec (~700 km at 44 AU) and {\Delta}m less than or equal to 0.5.

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Title: The Debiased Kuiper Belt: Our Solar System as a Debris Disk
Author: S. M. Lawler, the CFEPS Team

The dust measured in debris disks traces the position of planetesimal belts. In our Solar System, we are also able to measure the largest planetesimals directly and can extrapolate down to make an estimate of the dust. The zodiacal dust from the asteroid belt is better constrained than the only rudimentary measurements of Kuiper belt dust. Dust models will thus be based on the current orbital distribution of the larger bodies which provide the collisional source. The orbital distribution of many Kuiper belt objects is strongly affected by dynamical interactions with Neptune, and the structure cannot be understood without taking this into account. We present the debiased Kuiper belt as measured by the Canada-France Ecliptic Plane Survey (CFEPS). This model includes the absolute populations for objects with diameters >100 km, measured orbital distributions, and size distributions of the components of the Kuiper belt: the classical belt (hot, stirred, and kernel components), the scattering disk, the detached objects, and the resonant objects (1:1, 5:4, 4:3, 3:2 including Kozai subcomponent, 5:3, 7:4, 2:1, 7:3, 5:2, 3:1, and 5:1). Because a large fraction of known debris disks are consistent with dust at Kuiper belt distances from the host stars, the CFEPS Kuiper belt model provides an excellent starting point for a debris disk model, as the dynamical interactions with planets interior to the disk are well-understood and can be precisely modelled using orbital integrations.

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Title: Will New Horizons see dust clumps in the Edgeworth-Kuiper belt?
Author: Christian Vitense, Alexander V. Krivov, Torsten Löhne

Debris disks are thought to be sculptured by neighboring planets. The same is true for the Edgeworth-Kuiper debris disk, yet no direct observational evidence for signatures of giant planets in the Kuiper belt dust distribution has been found so far. Here we model the dust distribution in the outer solar system to reproduce the dust impact rates onto the dust detector onboard the New Horizons spacecraft measured so far and to predict the rates during the Neptune orbit traverse. To this end, we take a realistic distribution of transneptunian objects to launch a sufficient number of dust grains of different sizes and follow their orbits by including radiation pressure, Poynting-Robertson and stellar wind drag, as well as the perturbations of four giant planets. In a subsequent statistical analysis, we calculate number densities and lifetimes of the dust grains in order to simulate a collisional cascade. In contrast to the previous work, our model not only considers collisional elimination of particles, but also includes production of finer debris. We find that particles captured in the 3:2 resonance with Neptune build clumps that are not removed by collisions, because the depleting effect of collisions is counteracted by production of smaller fragments. Our model successfully reproduces the dust impact rates measured by New Horizons out to ~23AU and predicts an increase of the impact rate of about a factor of two or three around the Neptune orbit crossing. This result is robust with respect to the variation of the vaguely known number of dust-producing scattered disk objects, collisional outcomes, and the dust properties.

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Title: A study of the high-inclination population in the Kuiper belt - II. The Twotinos
Author: Jian Li, Li-Yong Zhou, Yi-Sui Sun

As the second part of our study, in this paper we proceed to explore the dynamics of the high-inclination Twotinos in the 1:2 Neptune mean motion resonance (NMMR). Depending on the inclination i, we show the existence of two critical eccentricities ea(i) and ec(i), which are lower limits for the eccentricity e for the resonant angle \sigma to exhibit libration and asymmetric libration, respectively. Accordingly, we have determined the libration centres \sigma_0 for inclined orbits, which are strongly dependent on i and could be very different from the zero-i case. With the initial \sigma=\sigma_0 on a fine grid of (e,i), the long-term stability of orbits in the 1:2 NMMR is probed by numerical integrations for the age of the Solar system. It is shown that symmetric librators are totally unstable for i\ge30°; while stable asymmetric librators do exist for i as high as 90°, and they generally have resonant amplitudes _{\sigma}<50°.
We further investigate the 1:2 NMMR capture and retention of planetesimals with initial inclinations i_0\le90° in the planet migration model using a long time-scale of 2x10^7 yr. We find that: (1) the capture efficiency of the 1:2 NMMR decreases drastically with the increase of i0, and it goes to 0 when i0exceeds ~60°; (2) the probability of discovering Twotinos with i>25°, beyond their observed values, is roughly estimated to be only ~0.1 per cent; (3) more particles are captured into the leading rather than the trailing asymmetric resonance for i_0\le10°, but this number difference appears to be the opposite at i0=20° and is continuously varying for even larger i0; (4) captured Twotinos residing in the trailing islands or having i>15° are practically outside the Kozai mechanism, like currently observed samples.

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Kuiper Belt Objects
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Title: Measuring the Abundance of sub-kilometre sized Kuiper Belt Objects using Stellar Occultations
Authors: Hilke E. Schlichting, Eran O. Ofek, Re'em Sari, Edmund P. Nelan, Avishay Gal-Yam, Michael Wenz, Philip Muirhead, Nikta Javanfar, Mario Livio

We present here the analysis of about 19,500 new star hours of low ecliptic latitude observations (|b| < 20 deg) obtained by the Hubble Space Telescope's FGS over a time span of more than nine years; which is an addition to the 12,000 star hours previously analysed by Schlichting et al. (2009). Our search for stellar occultations by small Kuiper belt objects (KBOs) yielded one new candidate event corresponding to a body with a 530 ±70m radius at a distance of about 40AU. Using bootstrap simulations, we estimate a probability of approx 5%, that this event is due to random statistical fluctuations within the new data set. Combining this new event with the single KBO occultation reported by Schlichting et al. (2009) we arrive at the following results: 1) The ecliptic latitudes of 6.6 deg and 14.4 deg of the two events are consistent with the observed inclination distribution of larger, 100km-sized KBOs. 2) Assuming that small, sub-km sized KBOs have the same ecliptic latitude distribution as their larger counterparts, we find an ecliptic surface density of KBOs with radii larger than 250m of N(r>250m) = 1.1^{+1.5}_{-0.7} x 10^7 deg^{-2}; if sub-km sized KBOs have instead a uniform ecliptic latitude distribution for -20 deg < b< 20 deg then N(r>250m) = 4.4^{+5.8}_{-2.8} x 10^6 deg^{-2}. This is the best measurement of the surface density of sub-km sized KBOs to date. 3) Assuming the KBO size distribution can be well described by a single power law given by N(>r) \propto r^{1-q}, where N(>r) is the number of KBOs with radii greater than r, and q is the power law index, we find q=3.8±0.2 for a KBO ecliptic latitude distribution that follows the observed distribution for larger, 100-km sized KBOs. 4) Regardless of the exact power law, our results suggest that small KBOs are numerous enough to satisfy the required supply rate for the Jupiter family comets.

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Title: A Divot in the Size Distribution of the Kuiper Belt's Scattering Objects
Authors: C. Shankman, B. Gladman, N. Kaib, J. J. Kavelaars, J.-M. Petit

Via joint analysis of a calibrated telescopic survey, which found scattering Kuiper Belt objects, and models of their expected orbital distribution, we measure the form of the scattering object's size distribution. Ruling out a single power-law at greater than 99% confidence, we constrain the form of the size distribution and find that, surprisingly, our analysis favours a very sudden decrease (a divot) in the number distribution as diameters decrease below 100 km, with the number of smaller objects then rising again as expected via collisional equilibrium. Extrapolating at this collisional equilibrium slope produced enough kilometre-scale scattering objects to supply the nearby Jupiter-Family comets. Our interpretation is that this divot feature is a preserved relic of the size distribution made by planetesimal formation, now "frozen in" to portions of the Kuiper Belt sharing a "hot" orbital inclination distribution, explaining several puzzles in Kuiper Belt science. Additionally, we show that to match today's scattering-object inclination distribution, the supply source that was scattered outward must have already been vertically heated to of order 10 degrees.

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Kuiper Belt Objects
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Title: The Colour Differences of Kuiper Belt Objects in Resonance with Neptune
Authors: Scott S. Sheppard (Carnegie Institution of Washington, Department of Terrestrial Magnetism)

New optical colours of 58 objects in mean motion resonances with Neptune show the various resonant populations have significantly different colour distributions. The 5:3 and 7:4 resonances have semi-major axes near the middle of the main Kuiper Belt and both are dominated by ultra-red material. The 5:3 and 7:4 resonances have statistically the same colour distribution as the low inclination "cold" classical belt. The inner 4:3 and distant 5:2 resonances have objects with mostly moderately red colours, similar to the scattered and detached disk populations. The 2:1 resonance, which is near the outer edge of the main Kuiper Belt, has a large range of colours with similar numbers of moderately red and ultra-red objects at all inclinations. The inner 3:2 resonance, like the outer 2:1, has a large range of objects from neutral to ultra-red. The Neptune Trojans (1:1 resonance) are only slightly red, similar to the Jupiter Trojans. The inner 5:4 resonance only has four objects with measured colours but shows equal numbers of ultra-red and moderately red objects. The 9:5, 12:5, 7:3, 3:1 and 11:3 resonances do not have reliable colour distribution statistics, though it appears noteworthy that all three of the measured 3:1 objects have only moderately red colours, similar to the 4:3 and 5:2 resonances. The different colour distributions are likely a result from the disruption of the primordial Kuiper Belt from the scattering and migration of the giant planets. The few low inclination objects known in the outer 2:1 and 5:2 resonances are mostly only moderately red. This suggests if the 2:1 and 5:2 have a cold low inclination component, the objects likely had a significantly different origin than the ultra-red dominated cold components of the cold classical belt and 5:3 and 7:4 resonances.

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Title: Water ice in the Kuiper belt
Authors: M.E. Brown, E.L. Schaller, W.C. Fraser

We examine a large collection of low resolution near-infrared spectra of Kuiper belt objects and centaurs in an attempt to understand the presence of water ice in the Kuiper belt. We find that water ice on the surface of these objects occurs in three separate manners: (1) Haumea family members uniquely show surfaces of nearly pure water ice, presumably a consequence of the fragmentation of the icy mantle of a larger differentiated proto-Haumea; (2) large objects with absolute magnitudes of H<3 (and a limited number to H=4.5) have surface coverings of water ice - perhaps mixed with ammonia - that appears to be related to possibly ancient cryovolcanism on these large objects; and (3) smaller KBOs and centaurs which are neither Haumea family members nor cold-classical KBOs appear to divide into two families (which we refer to as "neutral" and "red"), each of which is a mixture of a common nearly-neutral component and either a slightly red or very red component that also includes water ice. A model suggesting that the difference between neutral and red objects is due to formation in an early compact solar system either inside or outside, respectively, of the ~20 AU methanol evaporation line is supported by the observation that methanol is only detected on the reddest objects, which are those which would be expected to have the most of the methanol containing mixture.

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