Winter 2015

January 16, 2015

Shunichi Kamata, UCSC

Title: The early evolution of the Moon: Lunar Magma Ocean solidification and the Late Heavy Bombardment

January 23, 2015

Stanley Awramik, UC Santa Barbara

Title: Late Archean Lakes and the Archean Earth System

January 30, 2015

Ana Cristina Aguiar, Stanford

Title: PageRank for earthquakes

February 6, 2015


Title: TBA

February 13, 2015

Tyler Robinson, NASA Ames

Title: A "0.1 bar Tropopause Rule" in Thick Atmospheres of Planets and Large Moons

February 20, 2015

Pablo Sobron, SETI Institute

Title: In-situ characterization of terrestrial analogues -- Science and technology for planetary robotic and manned exploration

February 27, 2015

Hiroko Kitajima, Texas A&M

Title: Stress state and physical properties along the megathrust plate boundary at the Nankai Trough

March 6, 2015

Desiree Cotto-Figueiroa, Arizona State University

Title: Self-Limitation of the YORP Effect and Scale-Dependent Studies of Meteorite Strength and Fragmentation


The Yarkovsky effect is a radiation recoil force that results in a semimajor axis drift in the orbit that can cause Main Belt asteroids to be delivered to powerful resonances from which they could be transported to Earth-crossing orbits. This force depends on the spin state of the object, which is modified by the YORP effect, a variation of the Yarkovsky effect that results in a torque that changes the spin rate and the obliquity. Extensive analyses of the basic behavior of the YORP effect have been previously conducted in the context of the classical spin state evolution of rigid bodies (YORP cycle). However, the YORP effect has an extreme sensitivity to the topography and even small centrifugally driven reconfigurations of aggregates can alter the YORP torque dramatically, resulting in spin evolution that can differ qualitatively from the rigid-body prediction.  I will present the results of the first self-consistent simulations of the coupled spin-shape evolution of small gravitational aggregates under the influence of the YORP effect.  One third of our simulations follow a simple evolution described as a modified YORP cycle. Two-thirds exhibit one or more of three distinct behaviors—stochastic YORP, self governed YORP, and stagnating YORP—which together result in YORP self-limitation. Self-limitation confines rotation rates of evolving aggregates to far narrower ranges than those expected in the classical YORP cycle, greatly prolonging the times over which objects can preserve their sense of rotation.  We conjecture that YORP self-limitation may inhibit formation of top-shapes, binaries, or both, by restricting the amount of angular momentum that can be imparted to a deformable body. Stochastic YORP, in particular, will affect the evolution of collisional families whose orbits drift apart under the influence of Yarkovsky forces
In addition, I will present results from an ongoing suite of scale-dependent studies of meteorite strength and fragmentation.  Many meteorite studies are focused on chemical and isotopic composition, which provide insightful information regarding the age, formation, and evolution of the Solar System. However, their fundamental mechanical properties have received less attention. It is important to determine these properties as they are related to disruption and fragmentation of bolides and asteroids, and activities related to sample return and hazardous asteroid mitigation.

March 13, 2015

Richard Alley, Penn State

Title: Over the Cliff?  The West Antarctic Ice Sheet and Sea Level Rise