Determination of organic and inorganic materials in cometary dust provides insight into the protosolar system environment and reveals clues to the process of planetary systems origins. Dust grains are reservoirs for condensable elements during their transport from the circumstellar winds of evolved stars, novae, and supernovae into ISM clouds that give rise to new stellar and planetary systems. Of all solar nebula bodies, comets contain the least processed materials, both ices and dust. The chemical composition and evolution of comet material can be studied during perihelion passage when solar irradiation enhances the production rate of volatile gases leading to the release of dust from the nucleus and the exposure of refractory material to ultraviolet (UV) flux. This research program is a comprehensive, systematic investigation of two distinct dynamical populations, Jupiter-family (JF) and Oort Cloud (OC) comets. This study of comet dust properties and physical characteristics will: (1) facilitate assessment of the importance of crystalline silicates as a diagnostic of solar nebula evolution and turbulent mixing models; and (2) explore whether comet dust mineralogy is correlated with observed organic volatile production rates.
Understanding how planetary formation occurs in protoplanetary disks is a scientific challenge for the astrophysical community. This initiative contributes to broad cross-disciplinary areas of inquiry. First, the determination and inter-comparison of grain properties in OC and JF comets enable study of the processes that determine the characteristics of bodies in the Solar System and the operation and interaction of these processes. Secondly, comets provide insight into the initial processes of planetesimal aggregation and planet building in the early solar nebula. Specifically, the thermal history of dust grains extant in the early solar nebula can be probed by constraining the properties of dust from comets. Lastly, this program will test the new hypothesis, arising out of comparison of the investigators' observations of the Deep Impact target 9P and the split comet 73P with recent studies of comet gas-phase organics, that comet taxonomy based on current orbital (dynamical) classification should be supplanted by a taxonomy based on physical characteristics of dust mineralogy and grain properties and organic composition and super-volatile production rates.
This program creates an environment for educational mentoring activities in experimental techniques and observational astrophysics at large public institutions with diverse student populations and talent bases. Research opportunities provide an infrastructure to promote student development as scientists and critical thinkers while exposing individuals to how scientific discourse, intellectual exchange, and public outreach are conducted in a dynamic environment of contemporary astrophysics. The investigators' students will utilize a variety of facilities to collect observational data, and participate directly with scientific analyses and dissemination. These activities contribute to workforce development and imparts to aspiring astronomers (and/or students with scientific/technical career objectives) observational and technical expertise, computer programming skills, and analysis methodology. Astronomy, in part because of its stunning imagery, provides a natural gateway for engaging the public in scientific discussions, and helps to foster a broad appreciation for the impact of science and technology. The researchers will disseminate research highlights to the public through a number of education and public outreach activities and venues. ***
The study of planet building in protoplanetary disks is an emerging area of research. The number of detected exo-planetary systems continues to increase and the inventory of dust mineral composition, organic materials, water abundances, ices, and gas content in the planet forming regions is now routinely determined from remote sensing spectrophotometry. However, the process by which micron-sized dust grains, volatile ices, and gas coalesce, aggregate, and grow leading to large planet-sized bodies is not well understood. Solar System formation is an engine that simultaneously preserves and transforms interstellar medium (ISM) dust grains into planetesimals and, ultimately, planets. A mixture of ISM dust and solar nebula processed materials; comets enable us to investigate both the inputs and outputs of dust transformation in the young Solar System. Comets are reservoirs of the most primitive materials in our Solar System. Their volatiles and dust have remained essentially unaltered since their incorporation into comets during the era of planet formation. As relics from the epoch of planet-building, and their dynamical and physical characteristics contain important information about the nature of planet formation in the Solar System. Our NSF-supported research (AST:076980, a collaborative research between CoIs at three Universities) focused on assessing the physical composition of cometary nuclei and comae using ground and space-based optical-infrared remote sensing techniques, thermal and scattering emission models, and supercomputer computational approaches. One unexpected and transformative intellectual result of our NSF supported study was that cometary dust species excavated from the sub-surface interior of the comet 9P/Tempel 1 (a short period comet [~4.5 yr period], thought to be highly processed by frequent perihelion passages near the Sun) were similar those found in some extremely primitive Oort cloud comets (nuclei that have only had minimal orbital passes into the interior regions our planetary system over the lifetime of the Solar System). This similarity strongly indicates that the origins if these two, dynamically distinct comet families either was the same in the proto-planetary disk, or that large scale radial mixing of materials occurred in the early solar system. Our result, combined with analysis of in situ sample returned by the NASA Stardust mission, has cased a reset in the paradigm used to describe the formation processes of planetismals within our Solar System – small bodies that eventually accreted and grew over time to form planets. Outcomes included dissemination of our findings in over 17 peer-reviewed articles, three (3) doctoral dissertations, numerous conference proceeds and abstracts, as well as international astronomical electronic circulars and reports. On-line data bases created as part of this research project are curated and are publically available through meta-links from journals and the Planetary Data Service (PDS) node. Science highlights were also incorporated into public outreach events and used as materials in new classroom activities. The remote sensing ground-based telescope network used to conduct observations in support of the NSF science program were also used to compliment and support space-based small-body rendezvous and encounter activities including the NASA LCROSS (lunar impactor), NASA Deep Impact (comet encounter), NASA EPOXI (comet rendezvous) missions and the European Space Agency Rosetta (comet rendezvous) platform. Workforce development, education, and STEM training was also an activity-focus (commensurate with requirements related to the broader impacts of the work as defined in the NSF merit review criteria) throughout the tenure of the NSF support. In part, grant funds supported 3 Ph.D. students and 4 undergraduates research students (including one future STEM K-12 teacher), enabled the establishment of international collaborative development, and scientific teaming opportunities with federally supported national centers (e.g., NASA Ames, NASA Goddard, and the International Gemini Observatory).
