Tuesday, March 29, 2016
4:00 pm
South Mudd 365

Planetary Science Seminar

Celestial mechanics, impacts, and observations of small body populations
Sarah Greenstreet, Department of Physics, UCSB

Studying the orbital dynamics of small body populations in the Solar System allows us to understand both their current population and past orbital structure. Planet-crossing populations can provide impact speeds and probabilities and when coupled to cratering histories of solid bodies can provide planetary surface ages. Observational studies of near-Earth objects (NEOs) can provide a better understanding of their size-frequency distribution, which can constrain formation and evolution models, as well as characterization studies through lightcurve and rotation period measurements.

Motivated by Canada's Near-Earth Object Surveillance Satellite (NEOSSat), our new NEO orbital distribution model (Greenstreet et al. 2012) has larger statistics that permit finer resolution and less uncertainty, especially in the a < 1.0 AU region, than the previous model (Bottke et al. 2002) provides. The Wide-field Infrared Survey Explorer Near-Earth Object (NEOWISE) detections of the NEO orbital distributions (Mainzer et al. 2012) have been used to illustrate that this pure-gravity NEO orbital model is not rejectable (at >99% confidence). Thus, no non-gravitational physics is required to model the NEO orbital distribution. In addition, our integrations uncovered two previously undiscussed populations of NEOs: Venus-decoupled NEOs (Vatiras), which make up ~0.22% of the steady-state NEO population and the unexpected production of retrograde orbits from main-belt asteroid sources; this retrograde NEA population makes up ~0.1% of the steady-state NEO population.

Moving to the outer Solar System, the recent New Horizons spacecraft fly-through of the Pluto system in July 2015 is providing humanity's first chance to study crater populations produced by the multitude of Kuiper belt sub-populations due to Pluto's unique location within the Kuiper belt. We compute impact and cratering rates onto Pluto and Charon from the Kuiper belt sub-populations, finding that four sub-populations dominate Pluto's impact flux, each providing ~15-20% of the total rate. In addition, we provide model-dependent ages for four Kuiper belt size distribution models.

On the observational side, the Las Cumbres Observatory Global Telescope (LCOGT) network's global coverage and the apertures of telescopes available make LCOGT ideal for follow-up and characterization of Solar System objects (e.g. asteroids, Kuiper Belt Objects, comets, NEOs) and ultimately for the discovery of new objects. The LCOGT Solar System group is using the network to confirm newly detected NEO candidates produced by the major sky surveys such as Catalina Sky Survey, PanSTARRS, and NEOWISE, with several hundred targets being followed per year. Follow-up astrometry and photometry of radar-targeted objects and those of interest to NASA are improving orbits, producing light curves and rotation periods, and better characterizing these NEOs. In addition, we are in the process of building a NEO portal that will allow professionals, amateurs, and Citizen Scientists to plan, schedule, and analyze NEO imaging and spectroscopy observations and data using the LCOGT Network and to act as a coordination hub for the NEO follow-up efforts.

Contact Chris Spalding cspaldin@caltech.edu
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