[IGPP Everyone] [EPSS Everyone] Planetary Science Seminar this Week

[Kevin McKeegan]

This week we'll have a possible double-feature starring our own Ashley
Schoenfeld:


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*PLANETARY SCIENCE SEMINAR*

*Thursday, May 31*

*noon in Slichter 3853*

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* Ashley Schoenfeld*

*UCLA/EPSS*


*“First tectonic stress map across Enceladus' SPT and possible dynamic
causes"*


Enceladus is a small moon of Saturn (radius ~250 km), distinguished by its
uniquely active south pole. The moon’s geological activity is expressed as
regularly erupting plumes sourced from a series of parallel ‘‘tiger-stripe”
fractures (TSF) (Porco et al., 2006). The cyclic nature of these eruptions
are attributed to diurnal variations of tidal stress (Hurford et al.,
2007). There is, however, a mismatch in timing between Cassini’s
observations of peak eruption and what is predicted by the theory of
tidally modulated cracks (Nimmo et al., 2014). Existing models have
attempted to reconcile the plume timing discrepancy by invoking stress
relaxation in a viscoelastic ice sell (Běhounková et al., 2015). However,
such an approach assumes the stress in the ice shell to be entirely induced
by tidal stress, neglecting the role tectonically induced stress play in
order to support the high (>1 km) topographic relief around the moon’s
south pole (Schenk and McKinnon, 2009). We propose to address this by
relaxing the assumption of a tectonic stress-free ice shell and
offering an analytical
tensor analysis decomposing tidal and tectonic stresses in the ice shell. We
thus investigate the total stress as a result of three sources: tidal
stress from a bulged figure, stress induced by physical libration (Hurford
et al., 2009), and tectonic stress. With the aforementioned framework, we
derive the magnitude and direction of tectonic stress at numerous points
along the active TSFs, resulting in a comprehensive tectonic stress map of
Enceladus’ South Polar Terrain (SPT).

-----  possible second feature!  ------

*"Map to it! Finalizing the Titan Global Map"*

We have carried out detailed geomorphological mapping of Titan’s
mid-latitude and polar regions, approaching completion of Titan’s first
detailed global geomorphological map. We use radar data collected by
Cassini’s Synthetic Aperture Radar (SAR) as our basemap, supplemented by
images from VIMS, ISS, SARtopo, and radiometry datasets. We mapped at a
scale of 1:800,000, taking into consideration the 300 m/pixel resolution of
the swaths. We have defined six broad classes of mapping units, building
from those initially described in Malaska et al. (2016). These main units
are craters, hummocky/mountainous, labyrinth, plains, dunes, and
basin/lakes. Stratigraphic relationships deduced from our mapping suggest
that the hummocky/mountainous terrains are the oldest unit on Titan’s
surface, with radiometric signatures consistent with icy materials. Dunes
are the youngest unit and return a radiometric signature consistent
with organic sediments. Furthermore, our mapping suggest that the
equatorial and mid-latitudes of Titan are dominated by organic materials
being deposited and emplaced by aeolian activity, while the poles are
dominated by fluvial and lacustrine processes.



--
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Kevin D. McKeegan
Professor of Cosmochemistry & Geochemistry
Dept. of Earth, Planetary, and Space Sciences
UCLA
Los Angeles, CA 90095-1567
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mckeegan at epss.ucla.edu
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