Collisions are a fundamental process in the origin and evolution of planetary systems. For this reason, investigating impacts and impact outcomes is a prerequisite for accurately modeling the formation and evolution of planetary bodies. The inventory of satellites orbiting small Solar System bodies provides critical constraints that can be used to understand small body collisions. The ongoing work of this team represents the first systematic investigation of binary asteroid formation and produces modeled satellite systems and families of collision fragments consistent with those observed in the main asteroid belt. The research with this award will make the numerical models of asteroid satellite formation increasingly more realistic, in order to address several fundamental issues about binary asteroid formation that are still not fully understood and to enhance the ability to compare modeled binary properties with the ever increasing variety of observed asteroid satellite systems. The research team will investigate asteroid satellite and family formation via impacts onto rubble-pile targets (collisional evolution models suggest that most asteroids have been substantially fractured or shattered and reassembled by impacts since their formation), using the same numerical methods already employed to simulate solid-target impacts. Finally, the formation and survival of satellite systems during the late stages of planet formation will be investigated to determine the steady-state fraction of asteroid binaries capable of surviving from the planet formation epoch to today.
The work on this award will provide a strong synergistic link to existing observational programs that are detecting minor planet satellite systems at an ever-increasing rate. The work will help to understand the origin of the observed systems and will assist in directing future observations with scarce telescopic resources. The work continues to advance and solidify the partnerships formed between the Southwest Research Institute and The University of California Santa Cruz and The University of Maryland, and opens a new partnership with the Planetary Science Institute, providing an avenue through which scientists with different types of expertise can work together to achieve synergistic research results. The work will also continue intimate interaction with ongoing development of cutting-edge Artificial Intelligence (AI) techniques, in collaboration with JPL?s Machine Learning Group, aimed at improving the efficiency of numerical simulations. The many results of the ongoing research project have been presented to scientific colleagues at major, international astronomical meetings, and in journal papers and book articles in the peer-reviewed press. The research results are shared with students as research activities and results are incorporated into lecture and discussion material in college-level astronomy courses and in presentations in primary school classrooms where visually exciting results are shared with eager young students. Research results are also shared with the general public through extensive public outreach efforts that include television documentaries, radio interviews, and popular articles in magazines.
Main Objectives of the Research: Since collisions are such a fundamentally important process dominating the lives of individual asteroids and determining the evolution of the population of asteroids as a whole, understanding those impacts and their outcomes is a crucial part of deciphering the clues that asteroids hold in telling us about the origin and evolution of the Solar System. Since asteroid satellites are rather common, the roles that impacts may play in their formation can yield new insights into the impact process, the physical structure of asteroids, and the response of asteroids to those impacts. Asteroid satellites provide a direct measure of the total mass of the systems in which they reside (through application of Kepler’s Third Law). In those systems where the satellite is very small compared to the primary around which it orbits, that total system mass is dominated by the large primary. In other, double asteroid systems, where the two components may be more comparable in size, we can determine the individual masses if we have a means of determining the size ratio of the components and if we make the assumption that both components have the same density. If we can determine the actual dimensions of the primary or the components in the pair, we can use the mass to obtain a reliable estimate of the density. This is crucial, since density is a fundamental physical parameter that reveals much about the composition and physical structure of the asteroid and allows us to make comparisons between the asteroids and the inventory of meteorites we have in our collections here on Earth. Findings and Contributions: Our work has produced the highest fidelity numerical simulations yet conducted of the formation of asteroid satellites. Our models are allowing us to use the properties of observed satellites systems to narrow the possible starting conditions that could conceivably create such systems, and to gain valuable insights into how satellite formation and impact processes work. Collisions between asteroids violently fragment the target asteroids, locally in the case of cratering impacts and globally in the case of near-catastrophic ones. For even wholly catastrophic collisions some portion of the fragments can reaccumulate due to their feeble self-gravity. The result of these collisions can be a target asteroid that has evolved a structure more akin to a ‘pile of rubble’ than that of a solid monolithic slab of rock. Importantly, we have found that such ‘rubble pile’ structures may have a very different response to subsequent impacts, and thus different chances of forming satellites as a result of those impacts, than would solid asteroids. This different response to impacts will affect the collisional evolution of the asteroid population as a whole, and, more practically for us here at home, will affect any techniques and technologies we might develop to divert a potentially hazardous asteroid from an Earth-impact trajectory. Broader Impacts of the Research: Several methods have been proposed to prevent the impact of a threatening, potentially hazardous near-Earth asteroid with our planet, including impacting the asteroid with a high-speed spacecraft to deflect or divert its trajectory. Unfortunately , we still know very little about the response of an asteroid to such an impact. If we can learn more about the physical structure of the surfaces and interiors of small asteroids and how they response to such impacts, we will stand a much better chance of success in any future impact mitigation activities. This project has integrated research and education through the training of at least one graduate student and through incorporation of specific research results into numerous presentations for undergraduate courses and public talks and a number of nationally broadcast television science documentaries. The project has advanced partnerships between Southwest Research Institute, The University of California Santa Cruz, The University of Maryland, and The University of Alicante in Spain.
