Collisions are of key importance to our solar systems formation and its ongoing evolution, as all solid planetary objects are believed to result from collisional aggregation processes. During early stages of planetary growth, collisions occurred primarily among small objects, which were typically irregular in shape, and whose response to collisions was governed by internal strength and structure. As objects grew increasingly massive, compression due to self-gravity finally overcame internal strength, yielding objects whose collisional outcomes were controlled by gravitational interactions. The goal of this project is to develop a better understanding of the behavior of gravity-dominated collisions, in particular their ability to produce satellite systems. Both the Moon and Plutos large satellite, Charon, are generally believed to have formed through giant impacts. These collisional studies will utilize a numerical method known as smooth particle hydrodynamics (SPH). The work consists of two tasks. Task 1 involves improved modeling of an impact-origin of the Pluto-Charon system, which has very recently been revealed to be a quadruple system, with two small satellites exterior to Charon. Specific sub-tasks include 1) high-resolution simulations of an impact formation of the Pluto system, 2) accretion simulations of resulting orbiting material, and 3) an evaluation of the potential for resonant sweeping of outer moonlets by Charon. Constraints on the timing of a Pluto-Charon forming impact relative to Plutos capture into resonance with Neptune, and its ramifications for the early Kuiper Belt population, will also be explored. Task 2 is a generalized study of the production of satellites during gravity-regime collisions in the outer solar system, involving a much broader range of parameter space than prior studies, which have focused on the Earth-Moon or Pluto-Charon systems. The aim is to identify the regimes of satellite-to-primary mass ratio and satellite orbit radius that can be produced by impacts, and in so doing provide new constraints that may help to distinguish between impact vs. capture events as formation modes for the ever increasing number of known KBO binaries. This in turn may better constrain models of early outer solar system formation and evolution.
The work supported here has broad scientific import, due to its relevance to solar system formation processes and to the origin of the Earth and Moon. The impact of the findings expected here will be enhanced by the New Horizons mission to Pluto-Charon and the Kuiper belt, and ongoing KBO discoveries. Dr. Canup frequently participates in educational and public outreach projects that allow for the concepts studied here to be disseminated to students and the public. Results on the origin of Pluto-Charon are currently being provided to a TV documentary under development for the Science Channel on the New Horizons mission. Dr. Canup is currently serving as a scientific advisor to the American Museum of National History in New York in the development of a new show, Cosmic Collisions in which results of her impact simulations are directly utilized; this show will have an estimated total audience of greater than a million. Dr. Canup hopes that by participating in such projects she can also provide a positive role model for young women and girls interested in science. During the course of all of the proposed work, results will be openly disseminated through conference presentations and publications. The investigators will continue to develop their public-accessible website to include additional downloadable animations of impact simulations (which are often utilized by educators), as well as lay-person descriptions of the techniques utilized and basic results. In addition, they will continue their related outreach and educational activities described above. ***
