We present results from a continuing effort to understand activity drivers for the enigmatic Comet 29P/Schwassmann-Wachmann 1 (SW1). SW1 has been of interest since its discovery almost 100 years ago because of its nearly continuous, quiescent activity beyond the water-sublimation line and its highly variable, outburst activity while receiving a nearly constant insolation due to its low eccentricity orbit. These characteristics make SW1 a useful target for investigating both distant cometary activity drivers and also cometary outburst behavior. We approach answering these questions through a detailed analysis of SW1; first by measuring nucleus properties required for a more accurate nucleus thermophysical modeling and second, by applying thermal modeling to replicate its activity. Our project began with an analysis of Spitzer Space Telescope infrared observations of SW1 from 2003. Coma removal techniques when applied to the images provided nucleus photometry measurements. Application of the Near Earth Asteroid Thermal Model (NEATM) to these measured photometry values resulted in an effective nucleus radius of 32.3 ± 3.1 km and a thermal beaming parameter of 1.14 ± 0:22. These results indicated that SW1 is one of the largest Jupiter Family Comets and also has a relatively smooth overall surface and/or a low thermal inertia. We next placed constraints on the nucleus' spin state through analysis of evolution seen in the coma's morphological structure through two sets of outburst coma observations. The first set analyzed are from the Kitt Peak 2.1-m telescope taken ± 2 days after a major outburst in 2008. 3-D Monte Carlo coma modeling showed that the nucleus' spin period is on the order of days and/or the spin pole orientation was along the Earth's directions during observations. The second set are Hubble Space Telescope observations from 1996 taken ± 15 hours after a major outburst. Modeling similarly showed a rotation period on the order of days. Due to the observing geometry differing between the 2008 and 1996 observations, we conclude the rotation period lower limit must be on the order of days even if the spin-pole direction was directed along the sub-Earth direction during one set of observations. The nucleus properties measured or constrained by our project were incorporated into a thermophysical model to replicate the quiescent activity via the sublimation of the supervolatile species CO or CO2. A progenitor nucleus was thermally evolved in SW1's current orbit using different plausible nucleus interior compositional and layering schemes. We discuss results of this analysis and additionally possibilities for future thermal modeling efforts.


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Graduation Date





Fernandez, Yan


Doctor of Philosophy (Ph.D.)


College of Sciences



Degree Program

Physics; Planetary Sciences









Release Date

February 2019

Length of Campus-only Access


Access Status

Doctoral Dissertation (Open Access)