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Title: The Ratio of Retrograde to Prograde Orbits: A Unique Way to test Kuiper Belt Binary Formation Theories
Authors: Hilke E. Schlichting, Re'em Sari

With the discovery of Kuiper Belt binaries that have wide separations and roughly equal masses new theories were proposed to explain their formation. Two formation scenarios were suggested by Goldreich and collaborators: In the first, dynamical friction that is generated by the sea of small bodies enables a transient binary to become bound (L s mechanism); in the second, a transient binary gets bound by an encounter with a third body (L mechanism).
We show that these different binary formation scenarios leave their own unique signatures in the relative abundance of prograde to retrograde binary orbits. This signature is due to stable retrograde orbits that exist much further out in the Hill sphere than prograde orbits. It provides an excellent opportunity to distinguish between the different binary formation scenarios observationally.
We predict that if binary formation proceeded while sub-Hill velocities prevailed, the vast majority of all comparable mass ratio binaries have retrograde orbits. This dominance of retrograde binary orbits is a result of binary formation via the L s mechanism, or any other mechanism that dissipates energy in a smooth and gradual manner. For super-Hill velocities binary formation proceeds via the $L mechanism which produces a roughly equal number of prograde and retrograde binaries.

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Title: A Search for sub-km KBOs with the Method of Serendipitous Stellar Occultations
Authors: S.J. Bickerton, J.J. Kavelaars, D.L. Welch

The results of a search for sub-km Kuiper Belt Objects (KBOs) with the method of serendipitous stellar occultations are reported. Photometric time series were obtained on the 1.8m telescope at the Dominion Astrophysical Observatory (DAO) in Victoria, BC, and were analysed for the presence of occultation events. Observations were performed at 40 Hz and included a total of 5.0 star-hours for target stars in the ecliptic open cluster M35 (beta=0.9deg), and 2.1 star-hours for control stars in the off-ecliptic open cluster M34 (beta=25.7deg). To evaluate the recovery fraction of the analysis method, and thereby determine the limiting detectable size, artificial occultation events were added to simulated time series (1/f scintillation-like power-spectra), and to the real data. No viable candidate occultation events were detected. This limits the cumulative surface density of KBOs to 3.5e10 deg^{-2} (95% confidence) for KBOs brighter than m_R=35.3 (larger than ~860m in diameter, assuming a geometric albedo of 0.04 and a distance of 40 AU). An evaluation of TNO occultations reported in the literature suggests that they are unlikely to be genuine, and an overall 95%-confidence upper limit on the surface density of 2.8e9 deg^{-2} is obtained for KBOs brighter than m_R=35 (larger than ~1 km in diameter, assuming a geometric albedo of 0.04 and a distance of 40 AU) when all existing surveys are combined.

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The farthest reaches of our solar system remain the most mysterious areas around the sun. Solving the mysteries of the outer solar system could shed light on how the whole thing emerged as well as how life on Earth was born.
Why the rainbow of colours in the Kuiper belt?
For instance, the Kuiper belt past Neptune is currently the suspected home of comets that only take a few decades or at most centuries to complete their solar orbits so-called "short-period comets." Surprisingly, Kuiper belt objects "show a wide range of colours neutral or even slightly blue all the way to very red," said University of Hawaii astrophysicist David Jewitt.

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Title: Detection of Small Kuiper Belt Objects by Stellar Occultations
Authors: R. Stevenson

Knowledge of the Kuiper Belt is currently limited to those objects that can be detected directly. Objects with diameters less than ~10km reflect too little light to be detected. These smaller bodies could contain most of the mass in the Kuiper Belt while the abundance of these bodies may constrain the distribution of mass. The overall size distribution of bodies within the Kuiper Belt can also be inferred from the relative abundances of sub-km and larger bodies. Stellar occultations are already used to study dark objects in the Solar System, such as asteroids or planetary rings. Occultation by a KBO of a size comparable to, or larger than, that of the Fresnel Scale will result in Fresnel diffraction. Detection of diffraction effects requires fast multiple-star photometry, which will be conducted in July 2007 using the Orthogonal Parallel Transfer Imaging Camera (OPTIC) mounted on the University of Hawaii 2.2m telescope on Mauna Kea. This paper details how knowledge of the mass and structure of the outer Solar System may be obtained through the detection of serendipitous stellar occultations.

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Title: Origin of the Structure of the Kuiper Belt during a Dynamical Instability in the Orbits of Uranus and Neptune
Authors: Harold F. Levison, Alessandro Morbidelli (OCA), Christa Van Laerhoven, Rodney Gomes, Kleomenis Tsiganis

We explore the origin and orbital evolution of the Kuiper belt in the framework of a recent model of the dynamical evolution of the giant planets, sometimes known as the Nice model. This model is characterized by a short, but violent, instability phase, during which the planets were on large eccentricity orbits. One characteristic of this model is that the proto-planetary disk must have been truncated at roughly 30 to 35 AU so that Neptune would stop migrating at its currently observed location. As a result, the Kuiper belt would have initially been empty. In this paper we present a new dynamical mechanism which can deliver objects from the region interior to ~35 AU to the Kuiper belt without excessive inclination excitation. Assuming that the last encounter with Uranus delivered Neptune onto a low-inclination orbit with a semi-major axis of ~27 AU and an eccentricity of ~0.3, and that subsequently Neptune's eccentricity damped in ~1 My, our simulations reproduce the main observed properties of the Kuiper belt at an unprecedented level.

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Title: Physical Properties of Kuiper Belt and Centaur Objects: Constraints from Spitzer Space Telescope
Authors: John Stansberry, Will Grundy, Mike Brown, Dale Cruikshank, John Spencer, David Trilling, Jean-Luc Margot
(Version v2)

Detecting heat from minor planets in the outer solar system is challenging, yet it is the most efficient means for constraining the albedos and sizes of Kuiper Belt Objects (KBOs) and their progeny, the Centaur objects. These physical parameters are critical, e.g., for interpreting spectroscopic data, deriving densities from the masses of binary systems, and predicting occultation tracks. Here we summarize Spitzer Space Telescope observations of 47 KBOs and Centaurs at wavelengths near 24 and 70 microns. We interpret the measurements using a variation of the Standard Thermal Model (STM) to derive the physical properties (albedo and diameter) of the targets. We also summarize the results of other efforts to measure the albedos and sizes of KBOs and Centaurs. The three or four largest KBOs appear to constitute a distinct class in terms of their albedos. From our Spitzer results, we find that the geometric albedo of KBOs and Centaurs is correlated with perihelion distance (darker objects having smaller perihelia), and that the albedos of KBOs (but not Centaurs) are correlated with size (larger KBOs having higher albedos). We also find hints that albedo may be correlated with visible colour (for Centaurs). Interestingly, if the colour correlation is real, redder Centaurs appear to have higher albedos. Finally, we briefly discuss the prospects for future thermal observations of these primitive outer solar system objects.

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Kuiper Belt Objects
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Title: The impact of the Kuiper Belt Objects and of the asteroid ring on future high-precision relativistic Solar System tests
Authors: Lorenzo Iorio
(Version v5)

We preliminarily investigate the impact of the Kuiper Belt Objects (KBOs) and of the asteroid ring on some proposed high-precision tests of Newtonian and post-Newtonian gravity to be performed in the Solar System by means of spacecraft in heliocentric ~ 1 AU orbits and accurate orbit determination of some of the inner planets. It turns out that the Classical KBOSs (CKBOS), which amount to ~ 70% of the observed population of Trans-Neptunian bodies, induce a systematic secular error of about 1 m after one year in the transverse direction T of the orbit of a test particle orbiting at 1 AU from the Sun. For Mercury the ratios of the secular perihelion precessions induced by CKBOs to the ones induced by the general relativity and the solar oblateness J_2 amount to 6 10^-7 and 8 10^-4, respectively. The secular transverse perturbation induced on a ~ 1 AU orbit by the asteroid ring, which globally accounts for the action of the minor asteroids whose mass is about 5 10^-10 solar masses, is 10 m yr^-1; the bias on the relativistic and J_2 Mercury perihelion precessions is 6.1 10^-6 and 1 10^-2, respectively. Given the very ambitious goals of many expensive and complex missions aimed to testing gravitational theories to unprecedented levels of accuracy, these notes may suggest further and more accurate investigations of such sources of potentially insidious systematic bias.

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Title: Physical effects of collisions in the Kuiper belt
Authors: Zoe M. Leinhardt, Sarah T. Stewart, Peter H. Schultz

Collisions are a major modification process over the history of the Kuiper Belt. Recent work illuminates the complex array of possible outcomes of individual collisions onto porous, volatile bodies. The cumulative effects of such collisions on the surface features, composition, and internal structure of Kuiper Belt Objects are not yet known. In this chapter, we present the current state of knowledge of the physics of cratering and disruptive collisions in KBO analogue materials. We summarize the evidence for a rich collisional history in the Kuiper Belt and present the range possible physical modifications on individual objects. The question of how well present day bodies represent primordial planetesimals can be addressed through future studies of the coupled physical and collisional evolution of Kuiper Belt Objects.

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Kuiper Belt Objects
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Title: Detectability of Occultation of Stars by Objects in the Kuiper Belt and Oort Cloud
Authors: T. C. Nihei (1 and 2), M. J. Lehner (2), F. B. Bianco (1 and 2), S.-K. King (3), J. M. Giammarco (4), C. Al**** (2) ((1) Dept. of Physics and Astronomy, University of Pennsylvania, (2) Harvard-Smithsonian Centre for Astrophysics, (3) Institute of Astronomy and Astrophysics, Academia Sinica, (4) Dept. of Physics, Temple University)

The serendipitous detection of stellar occultations by Outer Solar System objects is a powerful method for ascertaining the small end (r ~15 km) of the size distribution of Kuiper Belt Objects and may potentially allow the exploration of objects as far out as the Oort Cloud. The design and implementation of an occultation survey is aided by a detailed understanding of how diffraction and observational parameters affect the detection of occultation events. In this study, stellar occultations are simulated, accounting for diffraction effects, finite source sizes, finite bandwidths, stellar spectra, sampling, and signal-to-noise. Finally, the possibility of detecting small Outer Solar System objects from the Kuiper Belt all the way out to the Oort Cloud is explored for three photometric systems: a proposed space telescope, Whipple (Kaplan et al. 2003), the Taiwanese-American Occultation Survey (Lehner et al. 2006), and the Multi Mirror Telescope (Bianco 2007).

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Posts: 131433
Date:
RE: Kuiper Belt
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Title: The impact of the Kuiper Belt Objects and of the asteroid ring on future high-precision relativistic Solar System tests
Authors: Lorenzo Iorio
(revised v2)

We preliminarily investigate the impact of the Kuiper Belt Objects (KBOs) and of the asteroid ring on some proposed high-precision tests of Newtonian and post-Newtonian gravity to be performed in the Solar System by means of spacecraft in heliocentric \approx 1 AU orbits and accurate orbit determination of some of the inner planets. It turns out that the Classical KBOSs (CKBOS), which amount to \approx 70% of the observed population of Trans-Neptunian bodies, induce a systematic secular error of about 1 m after one year in the transverse direction T of the orbit of a test particle orbiting at 1 AU from the Sun. For Mercury the ratios of the secular perihelion precessions induced by CKBOs to the ones induced by the general relativity and the solar oblateness J_2 amount to 6 10^-7 and 8 10^-4, respectively. The secular transverse perturbation induced on a \approx 1 AU orbit by the asteroid ring, which globally accounts for the action of the minor asteroids whose mass is about 5 10^-10 solar masses, is 10 m yr^-1; the bias on the relativistic and J_2 Mercury perihelion precessions is 6.1 10^-6 and 1 10^-2, respectively. Given the very ambitious goals of many expensive and complex missions aimed to testing gravitational theories to unprecedented levels of accuracy, these notes may suggest further and more accurate investigations of such sources of potentially insidious systematic bias.

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