Coast Geological Society

Ventura, California

Please Join CGS on Tuesday October 15th, 2019

James H. Shirley, Jet Propulsion Laboratory - California Institute of Technology, will give his talk titled:

Europa's Surface Compostition: Active Icy Moons Geology with Exogenic 'Overprinting'


Europa (left) is the smallest of the four Galilean moons orbiting Jupiter. Global image mosaic view of Europa (right) with locations of the NIMS observastions.


Europa’s youthful icy surface has been driven by tectonic and thermal processes, yielding a considerable diversity of geologic forms.  The surface has additionally been heavily weathered by exogenic processes, including by the implantation of ions and neutrals from Jupiter’s magnetosphere, with concomitant photolysis and radiolysis.  Impact gardening and the sputtering and redisposition of volatiles further modify the surface properties and composition.  

In this review we will briefly describe the evolution of our knowledge of Europa’s surface composition, from the largest scales to the smallest, and from the discovery of water ice on Europa up to the present day.  As one theme we will consider the relationships to the radiation environment of Europa’s inferred surface properties and composition.  We will also focus on the evidence for distinctive surface compositions, of endogenic origin, corresponding to mapped geologic units on Europa’s surface.  Stratigraphic relationships allow ‘relative’ age estimates in some regions, for instance where impact ejecta have mantled exposures of greater age.  In some locations, we may also detect anomalies of the percent abundance of the ‘patina’ of hydrated sulfuric acid, of exogenic origin, that likewise imply significant differences in the exposure ages of surface materials. Despite many years of focused investigations, the chemical composition of Europa’s endogenic non-ice materials is unknown, and controversial; the results of both linear and intimate mixture modeling studies are non-unique and are thus ambiguous.  Nonetheless our current knowledge can provide a number useful insights of relevance for future remote sensing and in-situ investigations.

James H. Shirley


Jim Shirley has spent the past quarter-century working as a planetary Scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California.  His most recent research has focused on the causes and consequences of global dust storms on Mars.  Jim is also recognized as an authority on the surface geology and composition of Jupiter’s moon Europa, having authored or co-authored 10 published scientific studies on that topic.  Jim holds degrees from Berkeley and from CSUN, where he completed an interdisciplinary program in geology and physics in 1995.

Jim’s scientific interests range widely.  He has also published scientific studies of the Sun and solar physics, of the Earth’s atmosphere, and of large earthquakes and moonquakes.  Jim is married, with twin daughters, and currently lives in Simi Valley, California.

Read more about James on the JPL website HERE

The monthly CGS meeting is held at the Poinsettia Pavilion in Ventura!

Meeting Schedule:

6:00 - 7:00 PM: Social Hour - Snacks and Beverages 

7:00 - 7:30 PM: Dinner Service

7:30 - 8:00 PM: Announcements & Raffle

8:00 - 9:00 PM:  Main Presentation

CGS is proud to be affiliated with the PSAAPG