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Abstracts of the 50Th DDA Meeting (Boulder, CO) Abstracts of the 50th DDA Meeting (Boulder, CO) American Astronomical Society June, 2019 100 — Dynamics on Asteroids break-up event around a Lagrange point. 100.01 — Simulations of a Synthetic Eurybates 100.02 — High-Fidelity Testing of Binary Asteroid Collisional Family Formation with Applications to 1999 KW4 Timothy Holt1; David Nesvorny2; Jonathan Horner1; Alex B. Davis1; Daniel Scheeres1 Rachel King1; Brad Carter1; Leigh Brookshaw1 1 Aerospace Engineering Sciences, University of Colorado Boulder 1 Centre for Astrophysics, University of Southern Queensland (Boulder, Colorado, United States) (Longmont, Colorado, United States) 2 Southwest Research Institute (Boulder, Connecticut, United The commonly accepted formation process for asym- States) metric binary asteroids is the spin up and eventual fission of rubble pile asteroids as proposed by Walsh, Of the six recognized collisional families in the Jo- Richardson and Michel (Walsh et al., Nature 2008) vian Trojan swarms, the Eurybates family is the and Scheeres (Scheeres, Icarus 2007). In this theory largest, with over 200 recognized members. Located a rubble pile asteroid is spun up by YORP until it around the Jovian L4 Lagrange point, librations of reaches a critical spin rate and experiences a mass the members make this family an interesting study shedding event forming a close, low-eccentricity in orbital dynamics. The Jovian Trojans are thought satellite. Further work by Jacobson and Scheeres to have been captured during an early period of in- used a planar, two-ellipsoid model to analyze the stability in the Solar system. The parent body of the evolutionary pathways of such a formation event family, 3548 Eurybates is one of the targets for the from the moment the bodies initially fission (Jacob- LUCY spacecraft, and our work will provide a dy- son and Scheeres, Icarus 2011). They provide statis- namical context for the mission. Recent modeling tical analysis on the conditions for the bodies to en- has suggested that some members of the family have ter a stable orbit, reimpact, escape, or fission further, escaped the swarm on a time scale comparable to the forming a triple system. The planar, two-ellipsoid age of the Solar system. The aim of the present work model used in this study ignores higher order mass is to provide a dynamical simulation of the early his- parameters which have been shown to have signif- tory of the Eurybates family to explain its origins. icant influence on the dynamics of bodies in close Our modeling involved the creation of a 1000 mem- proximity. To understand the effect of these terms, ber synthetic fragment cloud, centered on 3548 Eury- we apply recently developed high-fidelity, computa- bates as the parent body. The synthetic family was tionally efficient full two-body problem (F2BP) mod- created using the Gauss equations, with a 100m/s elling tools, which allow us to represent each body as escape velocity and random ejection angles. The dy- an arbitrary mass distribution in three-dimensional namical evolution of the synthetic cloud was mod- space. With this tool we perform a Monte Carlo anal- eled using high precision n-body simulations with ysis for the evolution of an asymmetric binary sys- the REBOUND code on a variety of time scales. From tem from the point of fission until the system set- these simulations, we find that the synthetic family tles into a stable state or evolves further. During stabilizes into the modern observed libration pattern the dynamical simulations standard analytic meth- within a relatively short time span. By using statisti- ods for assessing asteroid breakup are used to assess cal comparisons with the observed family members, the spin rate of the system; the simulation is halted our results provide the first estimate of the minimum in the case of fission, reimpact, or escape. We select age of the Eurybates family. The Eurybates colli- 1999 KW4 as a test case because the shape, geome- sional family also provides a unique opportunity to try, and dynamics of the system have been well char- examine the dynamical evolution of the fragments of acterized and provide the knowledge necessary for 1 such a high-fidelity analysis. At the end of this pro- the system angular momentum and energy. To do cess we perform statistical analysis of the conditions this rigorous results from Celestial Mechanics are for binary evolutionary pathway and contrast our re- applied to determine the Hill Stability of a rubble sults with those of Jacobson and Scheeres. pile asteroid spun fast enough to disassociate into its component pieces. Depending on the overall energy 100.03 — The Dynamical Surface Environment of and angular momentum in the system, the number Tumbling Asteroids of components that can escape will be limited. If the rubble pile consists of N components, the en- 1 1 Daniel Brack ; Jay McMahon ergy required for different combinations of compo- 1 University of Colorado Boulder (Boulder, Colorado, United States) nents to escape can be related to the integer partitions of the number N. If the rubble pile is modeled as a Non-principal axis rotating asteroids, or tumbling size distribution with a given porosity, the energy asteroids, are a small subset of known asteroids, ob- required to disrupt the system into different clusters served both in the main asteroid belt and in near- can be reduced to a power series summation. This Earth orbit. In non-principal axis rotation a body’s talk reviews the application of Hill Stability theory angular velocity vector is not aligned with any of its to this problem and presents the overall conclusions principal axes, causing fluctuations in the evolution and their implications for forming asteroid pairs and of the angular velocity direction and magnitude of clusters. the body. For tumbling asteroids such fluctuations lead to a dynamic environment on their surfaces. 100.05 — The Dynamics of Surface Launched These dynamics manifest in an ever-changing geopo- Particles around Bennu tential, with surface accelerations and surface slopes changing magnitudes and directions. Research has Jay McMahon1; Daniel Scheeres1; Steven R. Chesley2; shown that tumbling is not a stable state for an aster- Andrew S. French1; Daniel Brack1; Davide Farnocchia2; oid and that it tends to dissipate throughout the as- Yu Takahashi2; Pasquale Tricarico3; Erwan Mazarico4; teroid’s lifetime. However, the existence of tumbling Dante S. Lauretta5 asteroids does point to some de-stabilizing mecha- 1 Smead Aerospace Engineering Sciences, University of Colorado nisms such as planetary flybys and the Yarkovsky– Boulder (Boulder, Colorado, United States) O’Keefe–Radzievskii–Paddack effect. The former be- 2 JPL (Pasadena, California, United States) ing an immediate impulsive mechanism and the lat- 3 PSI (Tucson, Arizona, United States) ter perturbing an asteroid’s rotation over millennia. 4 NASA Goddard Space Flight Center (Greenbelt, Maryland, We investigate the surface environment of several as- United States) teroids, both observed and hypothetical, combining 5 University of Arizona (Tucson, Arizona, United States) their angular velocity vectors and the shape models to examine the fluctuations in surface accelerations The OSIRIS-REx spacecraft has recently discovered and surface slopes. In addition, we examine motion small particles being ejected from the surface of the trends on the surfaces of such bodies, seeking to un- near-Earth asteroid Bennu. Observations to date derstand what would happen to particles placed on have shown that a number of particles have survived the surface as the asteroid tumbles and as the tum- in orbit for multiple days after leaving the asteroid bling state suddenly changes. The sudden change in surface, while others escape or quickly return to the tumbling state of asteroid (99942) Apophis is exam- surface. This behavior is governed by the complex ined in particular due to its expected flyby of Earth dynamical environment near the surface of small in 2029 and possibility of mass shedding after to the asteroids, as well as the constraints on the launch- encounter. ing conditions provided by the spacecraft observa- tions. This talk will explore the effects of the differ- 100.04 — Disassociation Energies for Rubble Pile ent forces that influence these trajectories, and will Asteroids demonstrate the surprising variety of orbits that can be produced in this environment. Daniel Scheeres1 1 Smead Aerospace Engineering Sciences, University of Colorado 100.06 — Earth’s missing Trojans: Lessons from Boulder (Boulder, Colorado, United States) Mars and the role of radiation forces We study the disassociation of rubble pile asteroids Apostolos Christou1 under rapid spin rates and the resultant asteroid 1 Armagh Observatory and Planetarium (Armagh, Northern Ire- pairs and clusters that can arise as a function of land, United Kingdom) 2 There is renewed interest in the possibility of stable 1 Arecibo Observatory (Arecibo, USA, Puerto Rico) Trojan asteroids of the Earth and observational con- 2 University of Central Florida (Orlando, Florida, United States) straints from the recent search by the OSIRIS-REx 3 Lunar and Planetary Institute (Houston, Texas, United States) spacecraft allow a population of at least several tens 4 Jet Propulsion Laboratory (Pasadena, California, United States) of few-hundred-m-sized such asteroids (Cambioni et al, 2018). These objects may represent leftover ma- Arecibo Observatory has the world’s most power- terial from the formation and early evolution of the ful planetary radar system, which provides ground- terrestrial planets (Malhotra, 2019). based observations whose quality could only be ex- If primordial terrestrial Trojans do exist, the clos- ceeded with a spacecraft flyby. It allows one to char- est analogue population within our solar system is acterize near-Earth objects (NEOs) in terms of size, probably the small retinue of Trojans hosted by Mars shape, spin, and surface properties, and to discover at moderate (15-30 deg) inclination, compared to the natural satellites that form binary and triple asteroid <10 deg inclination region where long-lived Earth systems.
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