Binary Near-Earth Asteroid Formation from Rotational Disruption of Gravitational Aggregates

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AST 0708110RichardsonDr. Derek Richardson, University of Maryland, will carry out a research program aimed at understanding the origin and evolution of binary near-Earth asteroids (NEAs). In previous NSF funded work, the research team established the binary NEA formation efficiency based on tidal encounters of fragile asteroids with Earth over a wide range of encounter parameters. They established that the steady-state number of binaries formed in this way is at most 2% of the total number of NEAs, compared to the observed 15%. This is motivation to determine whether improvements to the model or a new model entirely (such as thermally induced spin-up) is required to fully explain the observations. Four tasks will be carried out: 1) long-term integration of simulated binaries, including study of component shape effects, tidal evolution, and effect of realistic NEA orbits, to improve the sophistication of the steady-state model; 2) investigation of the effect of particle size/shape and aggregate strength on binary formation following rotational disruption, to assess which aspects enhance and which suppress binary formation; 3) determination of the efficiency of binary formation, incorporating results from Tasks 1 and 2; and 4) maintenance and dissemination of a public database of observations and simulations. The research team has developed a tool that quickly provides predictions of steady-state populations of binaries, including pre-existing binaries migrating in from the Main Belt, on the basis of inputs from other simulations. As new simulations are performed, the results are easily incorporated into the predictive algorithm. This provides a powerful way of testing the relative importance of a myriad of physical effects on binary production and evolution. No other group possesses the combination of high-performance simulation tools for gravity and collisions with analysis methods that can address the proposed research. In light of rapidly improving observations and new data from recent and forthcoming spacecraft missions, this theoretical study is an important component of understanding the nature and evolution of small bodies in the solar system.Results from this research are giving insight into the internal structure of NEAs and have implications for hazard mitigation strategies. If the properties of most if not all NEA binaries are consistent with a rotational disruption origin (so far at least some can be accounted for in this way), it will be established that NEAs in general must have very low tensile strength. Overall, a better understanding of NEAs in particular will lead to a better understanding of asteroids in general, and will therefore give insight into the formation and evolution of the building blocks of planets. If NEAs are indeed fragile assemblages of reaccumulated fragments, strategies for mitigating the hazard of such bodies colliding with Earth will be affected, and doubly so now that about 15% of NEAs are known to be binaries. Thus, this study has implications beyond just understanding the origin of binary NEAs. As an outreach component, a public repository of observed binary small bodies will be maintained along with educational resources to explain not only the research at the layman and student levels but also related aspects of small bodies in. The data will be updated on an ongoing basis and submitted to the NASA Planetary Data System annually. At least one new graduate student will join the team over the work period. The research will also build and strengthen partnerships between the Southwest Research Institute (through collaborator Bottke), University of Michigan (through collaborator Scheeres), and the University of Maryland.***