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RE: Double Asteroids
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Title: Main Belt Binary Asteroidal Systems With Circular Mutual Orbits
Authors: F. Marchis, P. Descamps, M. Baek, A.W. Harris, M. Kaasalainen, J. Berthier, D. Hestroffer, F. Vachier

In 2003, we initiated a long-term adaptive optics campaign to study the orbit of various main-belt asteroidal systems. Here we present a consistent solution for the mutual orbits of four binary systems: 22 Kalliope, 45 Eugenia, 107 Camilla and 762 Pulcova. With the exception of 45 Eugenia, we did not detect any additional satellites around these systems although we have the capability of detecting a loosely-bound fragment (located at 1/4 x RHill) that is ~40 times smaller in diameter than the primary. The common characteristic of these mutual orbits is that they are roughly circular. Three of these binary systems belong to a C-"group" taxonomic class. Our estimates of their bulk densities are consistently lower (~1 g/cm3) than their associated meteorite analogues, suggesting an interior porosity of 30-50% (taking CI-CO meteorites as analogues). 22 Kalliope, a W-type asteroid, has a significantly higher bulk density of ~3 g/cm3, derived based on IRAS radiometric size measurement. We compare the characteristics of these orbits in the light of tidal-effect evolution.

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Classical Transneptunian Objects
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Title: Evidence for Two Populations of Classical Transneptunian Objects: The Strong Inclination Dependence of Classical Binaries
Authors: Keith S. Noll, William M. Grundy, Denise C. Stephens, Harold F. Levison, Susan D. Kern

We have searched 101 Classical transneptunian objects for companions with the Hubble Space Telescope. Of these, at least 21 are binary. The heliocentric inclinations of the objects we observed range from 0.6-34 degrees. We find a very strong anticorrelation of binaries with inclination. Of the 58 targets that have inclinations of less than 5.5 degrees, 17 are binary, a binary fraction of 29 +7/-6%. All 17 are similar-brightness systems. On the contrary, only 4 of the 42 objects with inclinations greater than 5.5 degrees have satellites and only 1 of these is a similar-brightness binary. This striking dichotomy appears to agree with other indications that the low eccentricity, non-resonant Classical transneptunian objects include two overlapping populations with significantly different physical properties and dynamical histories.

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Title: Formation of Kuiper Belt Binaries
Authors: Hilke E. Schlichting, Re'em Sari
(Version v2))

The discovery that a substantial fraction of Kuiper Belt objects (KBOs) exists in binaries with wide separations and roughly equal masses, has motivated a variety of new theories explaining their formation. Goldreich et al. (2002) proposed two formation scenarios: In the first, a transient binary is formed, which becomes bound with the aid of dynamical friction from the sea of small bodies (Ls mechanism); in the second, a binary is formed by three body gravitational deflection (L mechanism). Here, we accurately calculate the Ls and L formation rates for sub-Hill velocities. While the Ls formation rate is close to previous order of magnitude estimates, the L formation rate is about a factor of 4 smaller. For sub-Hill KBO velocities (v << v_H) the ratio of the L to the Ls formation rate is 0.05 (v/v_H) independent of the small bodies' velocity dispersion, their surface density or their mutual collisions. For Super-Hill velocities (v >> v_H) the L mechanism dominates over the Ls mechanism. Binary formation via the L mechanism competes with binary destruction by passing bodies. Given sufficient time, a statistical equilibrium abundance of binaries forms. We show that the frequency of long-lived transient binaries drops exponentially with the system's lifetime and that such transient binaries are not important for binary formation via the L mechanism, contrary to Lee et al. (2007). For the Ls mechanism we find that the typical time, transient binaries must last, to form Kuiper Belt binaries (KBBs) for a given strength of dynamical friction, D, increases only logarithmically with D. Longevity of transient binaries only becomes important for very weak dynamical friction (i.e. D >~ 0.002) and is most likely not crucial for KBB formation.

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Nate Lust is a searcher. He's scanning the heavens with a 20-inch telescope, hoping to find a binary asteroid.
Then he'll get to name it.

"Within the next two years, I'll have found a binary asteroid that wasn't known before. They're fairly plentiful and not that many people are looking for them."

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Posts: 131433
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Title: Formation of Kuiper Belt Binaries
Authors: Hilke E. Schlichting, Re'em Sari

The discovery that a substantial fraction of Kuiper Belt objects (KBOs) exists in binaries with wide separations and roughly equal masses, has motivated a variety of new theories explaining their formation. Goldreich et al. (2002) proposed two formation scenarios: In the first, a transient binary is formed, which becomes bound with the aid of dynamical friction from the sea of small bodies (L _s mechanism); in the second, a binary is formed by three body gravitational deflection (L mechanism). Here, we accurately calculate the L _s and L formation rates for sub-Hill velocities. While the L _s formation rate is close to previous order of magnitude estimates, the L formation rate is about a factor of 4 smaller. For sub-Hill KBO velocities (v << v_H) the ratio of the L to the L _s formation rate is 0.05(v/v_H) independent of the small bodies' velocity dispersion, surface density and mutual collisions. For Super-Hill velocities (v >> v_H) the L mechanism dominates over the L _s mechanism. Binary formation via the L mechanism competes with binary destruction by passing bodies. Given sufficient time, a statistical equilibrium abundance of binaries forms. We show here that the frequency of long-lived transient binaries drops exponentially with the system's lifetime and that such transient binaries are not important for binary formation via the L mechanism, contrary to Lee et al. (2007). For the L _s mechanism we find that the typical time, transient binaries must last, to form Kuiper Belt binaries (KBB) for a given strength of dynamical friction, D, increases only logarithmically with D. Longevity of transient binaries becomes important only for very weak dynamical friction (i.e. D >= 0.002) and is most likely not crucial for KBB formation.

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Binary Centaur
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Title: The orbit, mass, size, albedo, and density of (65489) Ceto/Phorcys: A tidally-evolved binary Centaur
Authors: W.M. Grundy, J.A. Stansberry, K.S. Noll, D.C. Stephens, D.E. Trilling, S.D. Kern, J.R. Spencer, D.P. Cruikshank, H.F. Levison

Hubble Space Telescope observations of Uranus- and Neptune-crossing object (65489) Ceto/Phorcys (provisionally designated 2003 FX128) reveal it to be a close binary system. The mutual orbit has a period of 9.554 +/- 0.011 days and a semimajor axis of 1840 +/- 48 km. These values enable computation of a system mass of (5.41 +/- 0.42) 10^18 kg. Spitzer Space Telescope observations of thermal emission at 24 and 70 microns are combined with visible photometry to constrain the system's effective radius (109 +10/-11 km) and geometric albedo (0.084 +0.021/-0.014). We estimate the average bulk density to be 1.37 +0.66/-0.32 g cm^-3, consistent with ice plus rocky and/or carbonaceous materials. This density contrasts with lower densities recently measured with the same technique for three other comparably-sized outer Solar System binaries (617) Patroclus, (26308) 1998 SM165, and (47171) 1999 TC36, and is closer to the density of the saturnian irregular satellite Phoebe. The mutual orbit of Ceto and Phorcys is nearly circular, with an eccentricity <= 0.015. This observation is consistent with calculations suggesting that the system should tidally evolve on a timescale shorter than the age of the solar system.

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Double Asteroid Antiope
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Unique Data Collected on Double Asteroid Antiope
Combining precise observations obtained by ESO's Very Large Telescope with those gathered by a network of smaller telescopes, astronomers have described in unprecedented detail the double asteroid Antiope, which is shown to be a pair of rubble-pile chunks of material, of about the same size, whirling around one another in a perpetual pas de deux. The two components are egg-shaped despite their very small sizes.
The asteroid (90) Antiope was discovered in 1866 by Robert Luther from Dusseldorf, Germany. The 90th asteroid ever discovered, its name comes from Greek mythology. In 2000, William Merline and his collaborators found that the asteroid was composed of two similarly-sized components, making it a truly 'double' asteroid, one of the very first of this kind in the main belt of asteroids that lies between the orbits of Mars and Jupiter.

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Antiope
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VLT observations of the double asteroid (90) Antiope during 2004. The adaptive optics NACO instrument was used, allowing the astronomers to perfectly distinguish the two components and so, precisely determine the orbit. The two objects are separated by 171 km, and they perform their celestial dance in 16.5 hours. The adaptive optics observations could, however, never resolve the shape of the individual components as they are too small.
Credit ESO

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Posts: 131433
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Antiope
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Roping together observations from the world's largest telescopes as well as the small instrument of a local backyard amateur, astronomers have assembled the most complete picture yet of a pair of asteroids whirling around one another in a perpetual pas de deux.
In a paper to be published in the April 2007 issue of the journal Icarus, a team of University of California, Berkeley, and Paris Observatory astronomers depict the asteroid 90 Antiope as two slightly egg-shaped rubble piles locked in orbit, like two twirling dancers facing one another with linked arms.
This new view of Antiope is the culmination of research that started in 2003 and that eventually included data supplied by both professional and amateur astronomers from around the globe.

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Posts: 131433
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RE: Double Asteroids
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Title: Binaries in the Kuiper Belt
Authors: Keith S. Noll, William M. Grundy, Eugene I. Chiang, Jean-Luc Margot, Susan D. Kern

Binaries have played a crucial role many times in the history of modern astronomy and are doing so again in the rapidly evolving exploration of the Kuiper Belt. The large fraction of transneptunian objects that are binary or multiple, 48 such systems are now known, has been an unanticipated windfall. Separations and relative magnitudes measured in discovery images give important information on the statistical properties of the binary population that can be related to competing models of binary formation. Orbits, derived for 13 systems, provide a determination of the system mass. Masses can be used to derive densities and albedos when an independent size measurement is available. Angular momenta and relative sizes of the majority of binaries are consistent with formation by dynamical capture. The small satellites of the largest transneptunian objects, in contrast, are more likely formed from collisions. Correlations of the fraction of binaries with different dynamical populations or with other physical variables have the potential to constrain models of the origin and evolution of the transneptunian population as a whole. Other means of studying binaries have only begun to be exploited, including lightcurve, colour, and spectral data. Because of the several channels for obtaining unique physical information, it is already clear that binaries will emerge as one of the most useful tools for unravelling the many complexities of transneptunian space.

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TNObinary

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Posts: 131433
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Binary NEAs
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Title: Many binaries among NEAs
Authors: David Polishook, Noah Brosch

The number of binary asteroids in the near-Earth region might be significantly higher than expected. While Bottke and Melosh (1996) suggested that about 15% of the NEAs are binaries, as indicated from the frequency of double craters, and Pravec and Harris (2000) suggested that half of the fast-rotating NEAs are binaries, our recent study of Aten NEA lightcurves shows that the fraction of binary NEAs might be even higher than 50%.
We found two asteroids with asynchronous binary characteristics such as two additive periods and fast rotation of the primary fragment. We also identified three asteroids with synchronous binary characteristics such as amplitude higher than one magnitude, U-shaped lightcurve maxima and V-shaped lightcurve minima. These five binaries were detected out of a sample of eight asteroids observed, implying a 63% binarity frequency. Confirmation of this high binary population requires the study of a larger representative sample. However, any mitigation program that requires the deflection or demise of a potential impactor will have to factor in the possibility that the target is a binary or multiple asteroid system.

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