Geophysics and Tectonics Seminar - fall-2016

Sept. 30, 2016
noon - 12:50 p.m.
Geology 3814

Presented By:

• Ana Piso - UCLA

The composition of planets is determined by and tightly linked to the composition of the protoplanetary disk in which they form. In the first part of my talk, I will discuss giant planet formation through core accretion. In the second part, I will explore how the composition and evolution of protoplanetary disks may affect the formation and chemical composition of giant planets.

Oct. 7, 2016
noon - 12:50 p.m.
Geology 3814

Presented By:

• Mathieu Lapotre - Caltech

Large wind ripples on Mars are unlike any wind-blown sedimentary structures found in Earth’s sandy deserts. We propose that they form from the effect of wind drag on sand particles, such that preserved ripple stratification may shed light onto the early evolution of the martian atmosphere.

Oct. 14, 2016
noon - 12:50 p.m.
Geology 3814

Presented By:

• Alessandro Morbidelli - Nice Observatory

Solar System formation and evolution: hints on the origin of the diversity of planetary systems

I will present an outline of the major steps in the formation of the Solar System and its evolution towards the current structure:

First, the generation of a global dichotomy, with multiple small (~Mars-mass) planetary embryos in the inner part and multi-­Earth-­mass giant planet cores in the outer part.

Second, the onset of a dynamical barrier against the drift of icy particles into the inner system, due to the formation of proto-­Jupiter, which allowed the inner solar system to remain ice-­depleted despite the disk cooled during its evolution.

Third, the inward migration of Jupiter, followed by an outward migration phase at the appearance of Saturn, which might have played a fundamental role in sculpting the terrestrial planet formation region and the asteroid belt.

Fourth, the formation of Uranus and Neptune by mutual collisions of proto-cores trapped in resonance with Jupiter and Saturn.

Finally, the late dynamical instability of the giant planets, that placed them on their final orbits. This reconstruction of the history of the Solar System will serve as a guideline to discuss which evolutionary phases the most likely to lead to the great diversity observed among extrasolar planetary systems.

Oct. 21, 2016
noon - 12:50 p.m.
Geology 3814

Presented By:

• Erica Nesvold - Carnegie Institute of Washington

The HD 106906 system harbors an asymmetric disk and a very distant (>650 au) planetary-mass companion. We use collisional and dynamical simulations to investigate the interactions between the disk and the companion, and to use the disk’s observed morphology to place constraint’s on the companion’s orbit.

Oct. 28, 2016
noon - 12:50 p.m.
Geology 3814

Presented By:

• Tilman Spohn - Institute of Planetary Research, German Aerospace Center

We consider a model of the evolution of the Earth including the water cycle and continental growth along with mantle convection and thermal evolution. The water cycle and continental growth and erosion are strongly non-linear feedback cycles that are coupled through the subduction of water carrying sediments and oceanic crust. Mantle viscosity is taken temperature and water concentration dependent. We plot our results in a series of phase planes spanned by mantle water concentration and continental coverage. The system starts with one fixed point in the phase plane and evolves to three fixed points (attractors) after 2Ga. Of the three fixed points two are stable and one is unstable. The unstable fixed point represents the present Earth while the other two represent planets covered either mostly with oceans or mostly with continents. To model the effect of the biosphere we reduce the erosion rate while keeping other parameters constant. We find that in the latter case the system would evolve away from the unstable fixed point towards the mostly ocean world. One may speculate about the climate and the tectonic modes of these alternative Earths.

Nov. 4, 2016
noon - 12:50 p.m.
Geology 3814

Presented By:

• Melanie Barboni - UCLA

New isotopic measurements of lunar zircons require formation of the Moon within the first ~60 million years of solar system history. This age places the Moon-forming giant impact 100 million years earlier than many recent estimates.

Dec. 2, 2016
noon - 12:50 p.m.
Geology 3814

Presented By:

• Björn Davidsson - JPL

Measurements from the Rosetta spacecraft at comet 67P show a low density, bilobate body containing volatile gases in addition to water. I will discuss implications of the Rosetta data for comet formation models.