Geophysics and Tectonics Seminar - spring-2017

April 7, 2017
noon - 1 p.m.
Geology 3814

Presented By:

• Jessie Christiansen - Caltech

Elusive Earths: Taking the Galactic Exoplanet Census

Measuring the occurrence rate of extrasolar planets is one of the most fundamental constraints on our understanding of planets throughout the Galaxy. By studying planet populations across a wide parameter space in stellar age, type, metallicity, and multiplicity, we can inform planet formation, migration and evolution theories. The NASA Kepler mission was a space-based survey for transiting exoplanets, primarily focussed on measuring the occurrence rates of Earth-like planets orbiting Sun-like stars. I will describe our ongoing efforts to catalogue the exoplanets in the Kepler field, including characterizing the survey completeness and reliability, and summarize our progress towards measuring robust occurrence rates. I will also describe the opportunity afforded by the NASA K2 mission, the successor to the Kepler mission, to expand occurrence rate calculations into a wider stellar parameter space.

April 14, 2017
noon - 1 p.m.
Geology 3814

Presented By:

• Joseph O’Rourke - Caltech

Generating Magnetic Fields in Earth, Venus, and Super-Earth Exoplanets

Earth's global magnetic field has survived for at least 3.5 billion years, yet Venus lacks a dynamo today. I will explore possible explanations for this dichotomy and discuss related implications for the internal structure and evolution of massive, rocky exoplanets.

April 21, 2017
noon - 1 p.m.
Geology 3814

Presented By:

• Peter Martin - Caltech

Although the relative timing of surface processes on Mars is relatively well constrained, the absolute timing of these events remains uncertain due to the inherent limitations of crater counting geochronology. The Curiosity rover has the demonstrated ability to measure the bulk K-Ar ages of rocks; an age of 4.21±0.35 Ga was measured early in the mission. A recent sample collected by Curiosity contains a relatively large proportion of jarosite, so a two-step heating experiment was conceived to allow separate measurement of the plagioclase (detrital) and jarosite (authigenic) ages. The low-temperature step (authigenic) yields a bulk age of 1.72 [+0.34, -0.30] Ga, while the high temperate step revealed a plagioclase age of 3.5 [+0.8, -0.6] Ga. The unexpectedly young age of the authigenic materials suggests relatively recent fluid flow in Gale Crater.

April 28, 2017
noon - 1 p.m.
Geology 3814

Presented By:

• Lucio Mayer - University of Zurich

Challenges in computational planet formation; from disk instability to planetesimal formation.

I will discuss recent progress in modeling a number of important regimes in planet formation. First I will report on recent developments in the disk instability model for giant planet formation, which is attractive to explain extrasolar gas giants on wide orbits. I will show how new Lagrangian hydrodynamical techniques can solve the long standing issue of non-convergence of the critical cooling for disk fragmentation. The same hydro method allows to study the combination of self-gravity and MHD turbulence in disks, offering the intriguing possibility that angular momentum dissipation by MRI may promote gravitational instability. I will then discuss planetesimal formation scenarios, introducing a new drag-vorticity instability whereby vortices in disks can generate long-lived, large enhancements of dust density which could be the precursors of planetesimals. This scenario is alternative to the conventional streaming instability and can take place starting from a wider range of initial properties of the dust layer. Finally, with the help of a novel sub-grid model for the coagulation and fragmentation of dust grains implemented in our multi-fluid code, we show how the common practice of simulating only single grain sizes can lead to incorrect results for the transport of dust through the disk.

May 5, 2017
noon - 1 p.m.
Geology 3814

Presented By:

• Thomas Navarro - UCLA

A Global Climate Model (GCM) is a convenient and powerful tool for studying any planetary atmosphere. I will give three examples of its application for Mars and Venus. First, I will explain how the modeling of water ice clouds unravels the water cycle on Mars, today and in its recent past. Then, I will present techniques to reconcile a GCM with observations, in particular inside Martian dust storms. Finally, I will tackle the modeling of mysterious gigantic gravity waves recently seen on Venus.

May 12, 2017
noon - 1 p.m.
Geology 3814

Presented By:

• Marta Bryan - Caltech

Over the past decade surveys using a variety of techniques have uncovered a diverse array of exoplanet systems. Many of these new systems are difficult to explain within the framework of standard planet formation theories, and have forced theorists and observers alike to re-evaluate their narratives for planet formation and migration. For example, direct imaging surveys have discovered a growing population of extremely young, planetary-mass companions at separations of > 100 AU, which pose significant challenges to in-situ formation models. The rotation rates of these young giant planets provide a unique window into the late stages of accretion, and can provide clues to past formation histories as well as present-day properties such as planetary atmospheric composition or the presence of moons and rings. In this talk I will discuss my work using radial velocity, direct imaging, and high-resolution spectroscopy techniques to study long period gas giant planets as tracers of formation and migration histories of planetary systems.

May 26, 2017
noon - 1 p.m.
Geology 3814

Presented By:

• Yoonyoung Kim - Seoul National University

Some asteroids show comet-like activity, while some comets become dormant or extinct and look like asteroids. Representing the dormant comet study, I will present an effort to dig out dormant comets in the list of known asteroids and diagnose their physical and dynamical properties. As one of the active asteroid studies, I will present a new dust modeling analysis on active asteroid P/2010 A2, which was successful to reproduce the morphological evolution of the dust cloud over seven years. Interestingly, no object has been detected at the dust ejection point of this model in any observations. This result suggests that the precursor asteroid was shattered by an impact, leaving only the debris cloud.

June 2, 2017
noon - 1 p.m.
Geology 3814

Presented By:

• Prof. Geoff Blake - Caltech

Compared to the Sun and to the gas+dust composition of the interstellar medium from which the solar system formed, the Carbon and Nitrogen content of the bulk silicate Earth (mantle+hydrosphere+atmosphere) is reduced by several orders of magnitude, relative to Silicon. Evidence from primitive bodies as a function of distance from the Sun suggests that at least part of this depletion must occur early in the process of planetesimal assembly. With pioneering infrared and (sub)mm observations such as those enabled by ground-based 8-10m class telescopes (and in future the James Webb Space Telescope) and the Atacama Large Millimeter Array (ALMA), we can now examine the principal volatile reservoirs of gas rich disks as a function position within the disk and evolutionary state. Key to these studies is the concept of condensation fronts, or 'snow lines,' in disks - locations at which key volatiles such as water, carbon monoxide, or nitrogen first condense from the gas. This talk will review the observational characterization of snow lines in protoplanetary disks via both gas and dust tracers, especially recent ALMA observations, and highlight the laboratory astrophysics studies and theoretical investigations that are needed to tie the observational results to the delivery of volatiles to planetary surfaces in the habitable zones around Sun-like stars.

June 9, 2017
noon - 1 p.m.
Slichter 3853

Presented By:

• Chad Trujillo - Northern Arizona University

An undiscovered ~10 Earth mass planet in our solar system has been hypothesized to explain the orbital characteristics of about a dozen of the most distant Kuiper Belt Objects (KBOs) and Inner Oort Cloud Objects (IOCs). I'll present the observational evidence for the planet and explain why the evidence is unlikely to be due to observational bias. I've used the known KBOs and IOCs as an input for over two thousand dynamical simulations run on the Northern Arizona University High Performance Computing Cluster. These simulations suggest a probable search area for the planet of just a few hundred square degrees, about the apparent size of your outstretched hand against the sky. This fall, we should be able to confirm or rule out the hypothesized planet using Hyper Suprime-Cam on the Subaru 8 meter telescope on Mauna Kea, Hawaii and the Dark Energy Camera on the Blanco 4 meter telescope in Chile. Regardless of its discovery, additional distant KBOs and IOCs will be found and will help constrain future predictions.