Goals: investigations of the chemical composition and physical properties of comets are important because, in addition to revealing the characteristics of comets themselves, the composition and…

This is a grant awarded by the National Aeronautics and Space Administration (NASA) Shared Services Center to Lowell Observatory, a private non-profit research institution located in Flagstaff, Arizona. The $731,972 grant funds research into the chemical composition and physical properties of comets, which can provide insights into the early solar system and the evolution of life on Earth. The research will utilize a variety of observational techniques, including imaging, photometry, and spectroscopy, to study the nuclei, coma, and production rates of various comets. The proposed work includes planned investigations of comets that have been or are potential targets for NASA spacecraft missions. There is no set-aside designation for this award, and it is a grant for research rather than a contract for goods or services.

Goals: investigations of the chemical composition and physical properties of comets are important because, in addition to revealing the characteristics of comets themselves, the composition and structure of comets hold unique clues to conditions in the early solar nebula, the solar system's formation processes, and even the evolution of life on earth as influenced by comet impacts over the past 4.6 billion years. The goals of our proposed research are to understand the physical and chemical properties of comets by applying a variety of observational techniques. We particularly emphasize simultaneous or coordinated observations with different instrumentation. We aim to (1) measure the basic properties of cometary nuclei by studying comets whose dust comae are so anemic that the signal from the nucleus can be extracted, or are at sufficient distances such that the coma no longer dominates the signal, (2) measure and model coma jet morphology to determine the orientation of the rotational axis, the location of source regions, the lifetime and velocities of the observed species and their respective parents, and how the production of material from the surface of each nucleus varies with time and solar illumination, and (3) measure the composition and production rates of comets as a function of orbital motion. Due to the strongly inter-related aspects of these measurements, results from the proposed projects will enable US to significantly improve our understanding of the physical nature, location, and chemical composition of active source regions on the nucleus, and how these produce the observed coma phenomena. Previous results: we have had a number of accomplishments under current past funding including imaging, photometry, and/or spectroscopy of 20+ short-period and 10+ long-period comets. Our primary efforts included completing analyses of comet ison, performing support observations for rosetta target 67P/churyumov- gerasimenko, and studying several close-approaching comets - 209P/linear, 252P/linear, 45P/honda-mrkos-pajdusakova, and 41P/tuttle-giacobini-kresak - with multiple science goals. We'VE also recently completed a rotational study of 49P/arend-rigaux, and obtained additional nucleus data of 6P/d'arrest, 2P/encke, and 103P/hartley 2. Production rates were determined and images obtained of several other comets. Proposed research: in the proposed interval, we plan detailed investigations for a variety of comets, including several that have been or are potential NASA spacecraft mission targets. Nucleus studies will be made of comets 2P/encke, 6P/d'arrest, and 103P/hartley 2. Rotational periods and how they change with time will be measured and we will investigate claims for complex rotation and, when present, attempt to determine details of the specific rotational state involved. Coma imaging will be obtained for comets 21P/giacobini-zinner, 38P/stephan-oterma, 46P/wirtanen, and 88P/howell to study and model jet morphology; on-going observations of 41P/tuttle-giacobini-kresak will also be modeled under this grant. Expected results include the orientation of the rotation axis, the rotation period, the location and size of each source region, and the outflow velocity of the gas. Planned spectroscopy of wirtanen will be combined with similar data recently obtained for two other very close approaching comets -- 252P/linear and 45P/honda-mrkos-pajdusakova -- to measure the elusive species diatomic sulfur. A new, extremely high resolution spectrograph on our 4.3-m telescope, DCT, will be used to measure isotopic ratios and other properties in the brightest comets. Production rates will be obtained to investigate temporal trends and/or determine basic composition. Coordinated observations with other investigators will be pursued when practical. We will also obtain observations of newly discovered comets as circumstances warrant.