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Seminars & Events

Week of May 25, 2020
Memorial Day DIX Planetary Sciences Seminar
4:00 pm to 5:00 pm
GPS Yuk Lunch Seminar
12:00pm to 1:00pm
Seismo Lab Seminar
9:00 am to 10:00 am
Physical Oceanography Group Meeting
12:00pm to 1:00pm
Environmental Science and Engineering Seminar
4:00pm to 5:00pm
Geoclub Seminar Series
4:00 pm to 5:00 pm
Thesis Defense Seminar - Nathan Stein

DIX Planetary Science Seminar

Tuesdays from 4:00pm to 5:00pm
For more information, please contact Shreyas Vissapragada

"In Search of Clearer Skies? Clouds and Hazes of sub-Neptune Worlds"
Sarah Moran - PhD Candidate – Earth & Planetary Sciences, Johns Hopkins

Abstract: : Little experimental laboratory work has been done to explore the properties of photochemical hazes formed in exoplanets, despite their role in atmospheric chemistry and their subsequent possible impact on observations, both for those of current observatories like Hubble and in the future with JWST and ground-based observatories. I will present results of the composition of haze particles produced from exoplanet laboratory studies in the JHU PHAZER laboratory. We detected many complex molecular species in the haze particles, including those with prebiotic applications. I will discuss the implications of these chemical measurements as they compare to existing atmospheric models of exoplanet photochemistry. Additionally, our experimental exoplanetary haze analogues exhibit diverse physical properties, which may help us understand their role as potential cloud condensation nuclei and their role in subsequent atmospheric evolution. Finally, I will discuss how we can apply what we've learned from the laboratory into atmospheric models for existing and future observations of sub-Neptune-sized exoplanets.

" Dynamical tides in the Jovian System as revealed by Juno "
Benjamin Idini, Graduate Student – Geophysics, Caltech

Abstract: Since 2016, the Juno orbiter has been collecting measurements of Jupiter's gravity field with an exquisite accuracy not seen before in the exploration of any other giant planet. Preliminary analysis of doppler shifts from Juno's trajectory over 17 perijove passes suggest the presence of a non-hydrostatic component in the amplitude of the tides that the Galilean moons raise on Jupiter. In this presentation I will propose dynamical tides as a candidate to reconcile Juno measurements of Jupiter's gravitational field with tidal theory. Part of our analysis suggests that Europa and Io may be at resonance with inertial modes in Jupiter's interior. Furthermore, I will discuss our progress on using the measured non-hydrostatic component of tides to infer the extension of Jupiter's potentially diluted core.

"Hazy Spectra, Mass Loss Histories, and Formation of 'Super-Puffs'"
Yayaati Chachan, Graduate Student – Planetary Science,Caltech

Abstract: Extremely low density planets (‘super-puffs') are a small but intriguing subset of the transiting planet population. With masses in the super-Earth range (1—10 M$_{\oplus}$) and radii akin to those of giant planets (>4 R$_{\oplus}$), their large (10s of % by mass) envelopes may have been accreted beyond the water snow line and many appear to be susceptible to catastrophic mass loss. Both the presence of water and the importance of mass loss can be explored using transmission spectroscopy. However, despite being promising candidates for transmission spectroscopy, they seem to possess featureless near-infrared spectra. Here, we present newHST WFC3 spectroscopy and updated Kepler transit depth measurements for the super-puff Kepler-79d. Although we do not detect any molecular absorption features in the 1.1-1.7 $\mu$m WFC3 bandpass, the combination of Kepler and WFC3 data reveals the presence of a scattering signature. We use a microphysical haze model to show that photochemical hazes offer an attractive explanation for the observed properties of super-puffs like Kepler-79d, as they simultaneously render the near-infrared spectrum featureless and reduce the inferred envelope mass loss rate by moving the measured radius (optical depth unity surface during transit) to lower pressures. We revisit the broader question of mass loss rates for super-puffs and find that the age estimates and mass loss rates for the majority of super-puffs can be reconciled if hazes move the photosphere from the typically assumed pressure of ~10 mbar to ~10 $\mu$bar. Finally, we use dust evolution models to show that the protoplanetary disk conditions required for the acquisition of large envelopes by super-puffs may be realized beyond the water snow line. We conclude by discussing some ongoing work on the location dependence of envelope accretion by planetary cores and its consequences for planet formation. 

Q. Zhang, Caltech

Environmental Science and Engineering Seminar

Wednesdays from 4:00pm to 5:00pm
For more information, please contact: Joern Callies

"Developing a Method for Investigation of Accretion Product Formation from Hydroxy Peroxy Radical Self Reactions"
Sara Murphy, Graduate student, Caltech

Peroxy radicals (RO2), formed by oxidation of volatile organic compounds (VOCs), can undergo a wide variety of reactions in the troposphere, including reaction with NO, HO2, and other RO2 radicals. The relative importance of these reaction pathways determines the ultimate effect of these compounds on tropospheric chemistry and air quality. However, despite their importance, the rates and products of peroxy radical self-reactions (RO2 + RO2 reactions) remain largely uncertain. In this presentation, I will discuss my work towards developing a method to study the products and rates of peroxy radical reactions, and present initial results of experiments investigating the self-reactions of ethene and propene-derived hydroxy peroxy radicals.

" Aromatics in the Atmosphere "
Reina Buenconsejo, Graduate student, Caltech


Atmospheric aromatic compounds play an important role in the formation of secondary organic aerosol (SOA). The photooxidation mechanisms of aromatics such as benzene, toluene, and xylene have been well-studied over the past several decades. But does this well-studied mechanism hold true for other aromatics? This talk explores the chemistry of other atmospherically-relevant aromatics with more complicated constituent groups, and more specifically, shares preliminary results on oxidation studies of benzyl alcohol, a C7 compound used as a solvent in industrial processes and a common ingredient in personal care products.

Geoclub Seminar Series

Thursdays from 4:00pm to 5:00pm
For more information, please contact: Dustin Morris

"Evidence for microbially mediated phosphogenesis on an energetic carbonate platform — Bahia and Minas Gerais, Brazil"
Cecilia Sanders, Graduate Student – GPS

Abstract: Eastern Brazil's São Francisco Craton contains scattered remnants of an Ediacaran-age carbonate platform, overlying Cryogenian-age glacial diamictite. The cap carbonate sequence represented in these rocks is remarkable for its high-energy sedimentary structures, abundant allochems, and — most famously — its phosphatic cements, associated almost exclusively with distinctive digitate stromatolite patch reefs. In this talk, I will review the data I've collected that paint a picture of the world in which these rocks formed and make a preliminary case for microbially-mediated mechanisms of phosphogenesis in such a world.

"Using Neural Networks to Improve Raman Mineral Identifications"
Karen Pham, Undergraduate Student - GPS

***NOTE: This talk will be geared toward those with little to no knowledge of machine learning or other computational methods used.

Abstract: Raman spectroscopy is a quick analytical technique for identifying minerals with wide applications in geoscience and materials science research. Mineral classifications made from Raman spectra can be improved using various machine learning methods. In this project, we used Raman spectra from the RRUFF database to successfully train neural networks to identify a range of baseline-corrected and non-baseline-corrected spectra. In an effort to increase the accuracy of our neural networks, we also explored the process of automating the identification of incorrectly named minerals and low-quality data points in the RRUFF database. Our goal is to release a highly accurate alternative to the mineral identification program currently in use with the GPS Department's Raman spectrometer. Rather than get into the nitty-gritty details of neural networks, this talk will aim to give the audience a broad overview of the work done and focus on the implications of introducing neural networks (sometimes described as "black-box models") to mineral identifications.

"Sea level, ice sheets, and megafloods during the last deglaciation in North America: Insights from solid-Earth ice sheet interactions"
Tamara Pica, GPS Caltech

" Low temperature alteration and weathering of tectonically exposed mantle peridotite "
Peter Kelemen, Columbia

GPS Yuk Lunch Seminar

Wednesdays from 12:00pm to 1:00pm
For more information, please contact: Danica Adams


Dr. Renyu Hu, JPL


Dr. Eliot Young (Southwest Research Institute)

Physical Oceanography Group Meeting

Fridays from 12:00pm to 1:00pm
All welcome, contact Andy Thompson for details, andrewt@caltech.edu

Seismo Lab Seminar

Thursdays from 9:00 am to 10:00 am
For more information, please contact Seismo Seminar Committee.

"Insights into the mineralogy of the lower mantle using comparisons between global seismic tomography and geodynamic models"

Paula Koelemeijer, Royal Holloway University of London

Global tomography models routinely image seismic velocities at depth in the mantle. However, interpretations of these seismic velocities are not unique due to competing effects of temperature, composition and phase transitions. One way to still obtain insights into the structure of the mantle is by comparing seismic tomography models to predictions based on geodynamic models of mantle convection. These models serve to provide a reasonable temperature distribution, while the effects of different compositions can be investigated through hypothesis testing of particular scenarios. One important aspect to take into account in such comparisons is the limited resolution of global tomography models.

In my tomographic-geodynamic comparisons I focus on the mid and the lowermost mantle, where tomographic models consistently find a negative correlation between shear-wave velocity (Vs) and bulk sound velocity (Vc) variations. As temperature effects are expected to have a similar effect on these velocities, this observation has long served as argument for large-scale compositional variations. I will show instead that the phase transition from bridgmanite to post-perovskite has a stronger influence on the Vs-Vc correlations and can serve as a possible explanation in the deep mantle. However, the onset of the negative correlation occurs at shallower depths (~1800 km), which is not reproduced by either thermal or thermochemical models with post-perovskite. I hypothesise that the iron spin transition in ferropericlase, which has a strong effect on Vc, can resolve this mid mantle discrepancy. Although ferropericlase only forms ~20 % of the Earth's mantle, I will use new first principles calculations for the mixed spin state to show that this spin transition effect can be observed in global tomography and leads to an improved fit to seismic tomography.

"Real-time Propagation of Radially Isotropic ground motion Decay (PRIDE)"
Men-Andrin Meier , Associate Staff Seismologist at Caltech

Abstract Because of the high speed with which seismic waves propagate, Earthquake Early Warning (EEW) algorithms are barely fast enough to alert near-epicentral sites that tend to get hit with the highest shaking intensities. EEW efforts are further complicated by the fact that fully automated seismic monitoring involves complex and error-prone processing steps, such as seismic phase association. Wavefield-based EEW methods, such as the Propagation of Local Undamped Motion (PLUM), successfully avoid the difficult processing steps, but the warning times from established wavefield methods are inherently short. Here we propose a novel wavefield EEW method that builds on PLUM and that combines the simplicity and robustness of wavefield methods with the speed and predictive capabilities of source-based methods. The Propagation of Radially Isotropic ground motion Decay (PRIDE) method uses a generic maximum ground motion decay model to predict shaking levels around each site that experiences significant shaking. We use a data set of >85k strong motion records from 650 earthquakes with Mw 3.7 – 9.1 in various tectonic contexts from Japan to demonstrate how PRIDE can alert a larger fraction of sites than state-of-the-art methods, and provide significantly longer warning times. The improvement is particularly pronounced for large shallow crustal earthquakes, where PRIDE can provide gross warning times of 5 s or longer for 85%, 50% and 20% of sites with strong, very strong and severe shaking intensities, respectively. The method should also work reliably for out-of-network events, multiple simultaneous events and in networks with sparse and heterogenous sensor distribution.

Thesis Defense Seminars

For more information, please contact Julie Lee; jlee@gps.caltech.edu

Nathan Stein - May 29, 1:30 pm
"Investigation of Past Habitable Environments through Remote Sensing of Planetary Surfaces"

Members of the Ph.D. examining committee are: Bethany Ehlmann (chair), John Grotzinger (thesis adviser), Woody Fischer, Mike Lamb

Zoom meeting

Time: May 29, 2020 01:30 PM Pacific Time (US and Canada)

Join Zoom Meeting


Meeting ID: 928 3053 8926

Password: planets

Alistair Hayden - June 3, 9:00 am
"Exhumed fluvial deposits: New paleohydrological tools indicate long-duration fluvial activity on early Mars"

Members of the Ph.D. examining committee are: Woody Fischer (chair), Mike Lamb (thesis adviser), Bethany Ehlmann, John Grotzinger

Zoom meeting

Time: June 3, 2020 9:00 AM Pacific Time (US and Canada)

Zoom Link:


Meeting ID: 951 6273 5950

Password: 165553

Yanzhe Zhu - June 3, 1:00 pm
"3D Microfluidics for Environmental Pathogen Detection and Single-Cell Phenotype-to-Genotype Analysis"

Members of the Ph.D. examining committee are: Jared Leadbetter (chair), Mike Hoffmann (thesis adviser), Victoria Orphan, Kathuri Venkateswaran (non-Caltech/JPL)

Zoom meeting
Time: Jun 3, 2020 01:00 PM Pacific Time (US and Canada)

Join Zoom Meeting

Meeting ID: 977 9056 5337

Sean Mullin - June 8, 10:00 am
"Spatial and Temporal Dynamics of Microorganisms Living Along Steep Energy Gradients and Implications for Ecology and Geologic Preservation in the Deep Biosphere"

Members of the Ph.D. examining committee are: Woody Fischer (chair), Victoria Orphan (thesis adviser), Jared Leadbetter, Dianne Newman

Zoom meeting
Time: Jun 8, 2020 10:00 AM Pacific Time (US and Canada)

Join Zoom Meeting

Meeting ID: 995 9685 3682
Password: 330141

Gray Chadwick - June 9, 9:00 am

Members of the Ph.D. examining committee are: Woody Fischer (chair), Victoria Orphan (thesis adviser), Jared Leadbetter, Dianne Newman

Elizabeth Bailey - June 22, 10:00 am

Members of the Ph.D. examining committee are: Dave Stevenson (chair), Konstantin Batygin (thesis adviser), Mike Brown, Heather Knutson

Leah Sabbeth - June or July, tentative

Members of the Ph.D. examining committee are: Jean-Philippe Avouac (chair), Joann Stock (thesis adviser), Claire Bucholz, George Rossman, Brian Wernicke

Kyle Metcalfe - August, tentative

Members of the Ph.D. examining committee are: Jared Leadbetter (chair), Victoria Orphan (thesis adviser), Woody Fischer, George Rossman