Mar 23

"Turbulent Ordering and Collisions of Dust Grains: Results with Large Inertial Ranges"
Alexander Hubbard, American Museum of Natural History, New York, NY (Visiting Speaker)

The formation theory for rocky planets, and the core accretion theory of gas giant formation both require the collision and sticking of small dust grains to bridge the gap between sub-micron interstellar grains and boulders large enough for gravitational interactions to play a major role. For a broad range of dust grain sizes, these interactions occur in, and are forced by, turbulence in the host protoplanetary disk. These turbulence induced collisions have long been a topic of research, and basic theoretical approaches, combined with physical experiments, combine to raise, rather than answer, questions. Bluntly, the dust grains collide too fast, so they will bounce or shatter rather than stick. However, problem of turbulent dust collisions, like many turbulent phenomena, is in practice only accessible through numerical simulation. I will describe some limitations of current simulations as well as the results of a new method that bypasses them. The results suggest that violent collisions are less problematic than previously believed, showing a picture of highly clustered and correlated dust grains which will need to be taken into account for a variety of disk dynamics.

Apr 23

"Europa's Great Lakes"
Britney Schmidt, UT Austin: Jackson School of Geosciences

With an icy exterior covering a global ocean, Europa has long been a target of interest in the search for life beyond Earth. Europa exists in a dynamic environment, subject to intense irradiation and impact as well as immense tides from Jupiter. These processes deliver important thermal and chemical energy that could be critical to supporting a putative biosphere. In the past few decades the debate about habitability of Europa has been focused strongly on the thickness of the ice shell. However, an arguably more critical question is: how does the ice shell recycle? New analysis of Europa's enigmatic "chaos terrains," indicates that chaos features form in the presence of a great deal of liquid water, and that large liquid water bodies exist within 3km of Europa's surface comparable in volume to the Great Lakes. The detection of shallow subsurface "lakes" implies that the ice shell is recycling rapidly and that Europa may be currently active. In this presentation, we will explore environments on Europa and their analogs on Earth, from collapsing Antarctic ice shelves to to subglacial volcanos in Iceland. I will present these new analyses, and describe how this new perspective informs the debate about Europa's habitability and future exploration.