ABCDEF
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In
Planetary Science SEMINARS - Fall 2021
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Campus and bay-area speakers will present in person. Remote speakers will present over Zoom.
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Wednesdays 1:10-2:00 PM
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For a Zoom link to the meeting please contact: militzer @ berkeley . edu
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DateSpeakerAffiliationTitleAbstractHost
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25-AugMaggie Thompson (in person)UCSCTerrestrial Exoplanet Atmospheres: Outgassing Origins and Potential BiosignaturesThe next phase of exoplanet science will focus on characterizing exoplanet atmospheres, including those of low-mass, terrestrial planets. In this talk, I will discuss two ongoing projects that seek to better understand the origins of and potential biosignatures in terrestrial exoplanet atmospheres.

The first project is motivated by the fact that, at present, there is no first-principles understanding of how to connect a planet’s bulk composition to its initial atmospheric properties. Since terrestrial exoplanets likely form their atmospheres through outgassing, an important step towards building such a theory is to assay meteorites, the left-over building blocks of planets, by heating them to measure their outgassed volatiles. The Solar System presents a wide variety of meteorite types, including carbonaceous chondrites which are believed to be representative of the bulk material in the solar nebula during planet formation. To inform the initial chemical composition of terrestrial planet atmospheres, I will present the results of outgassing experiments in which we heated carbonaceous chondrite samples to 1200 ℃ and measured the abundances of released volatiles (e.g., H2O, CO, CO2, H2, H2S) as a function of temperature. We also performed complementary bulk element analysis on the samples before and after the heating experiments to monitor outgassing of heavier elements (e.g., Mg, Fe, Na, S). I will discuss how these experimental results compare to thermochemical equilibrium models of chondrite outgassing and how the experiments can help improve atmospheric models.

The second project focuses on methane, a potential biosignature gas for terrestrial exoplanet atmospheres. As we move into the era of JWST, a comprehensive understanding of possible biosignatures that may be detected with the next generation of ground and space-based telescopes is warranted. While some biosignature gases, such as oxygen, phosphine and ammonia, have recently been reviewed in depth, these will likely be extremely difficult to detect in high mean molecular weight atmospheres with JWST. In contrast, while it has not been thoroughly reviewed, methane at Earth-like biogenic fluxes is one of the only biosignatures that may be readily detectable with available near-term instruments. I will present our work on determining the necessary planetary context for methane to be a compelling biosignature. 		Marta Bryan
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1-SepMike Wong (in person)UCBEvolution of the Velocity Field of Jupiter's Great Red SpotWe measured the horizontal winds in Jupiter's Great Red Spot (GRS) at 11 time periods from 2009 to 2020, using Hubble Space Telescope time-series imaging. As an example of a "pancake vortex" with height much smaller than length, the GRS---and its interactions with its environment---share both similarities and differences with other solar system vortices embedded in stratified fluids with shear flow. These include terrestrial ocean eddies and atmospheric vortices on the other giant planets.
Our data show that there are long-term monotonic trends in size and shape of the high-speed ring marking the vortex dynamical boundary, as was previously noted from trends in the visible cloud appearance. We find a 4-8% increase in the mean wind speeds of the high-speed ring from 2009 to 2020. Shorter-term changes include variability in the shape of the high-speed ring, and changes in flow properties that may relate to a large convective outbreak horizontally distanced (but at similar latitude) in 2016-2017.		Burkhard Militzer
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8-SepDarryl Seligman (virtual)U ChicagoA Galactic Census of Minor Bodies: What Are They, How Do They Form, and Where Do They Come From?`Oumuamua (I1 2017) was the first macroscopic body observed to traverse the inner Solar System on an unbound hyperbolic orbit, making it the first interstellar object ever detected up close. `Oumuamua’s light curve displayed strong periodic variation, and it showed no hint of a coma or emission from molecular outgassing. Astrometric measurements indicate that `Oumuamua experienced non-gravitational acceleration on its outbound trajectory, but energy balance arguments indicate this acceleration is inconsistent with a water ice sublimation-driven jet. In the first part of this talk, I will show that all of `Oumaumua's observed properties can be explained if it contained a significant fraction of molecular hydrogen ice. I show that H2-rich bodies plausibly form in the coldest dense cores of Giant Molecular Clouds. I assess the near-term prospects for detecting and observing (both remotely and in-situ) future solar system visitors of this type. In the second part of this talk, I investigate the dynamical transfer of Centaurs into the inner Solar System, facilitated by mean motion resonances with Jupiter and Saturn. The recently discovered object, P/2019 LD2, will transition from the Centaur region to the inner Solar System in 2063. In order to contextualize LD2, I perform N-body simulations of a population of Centaurs and JFCs. The simulations show that there may be additional LD2-like objects transitioning into the inner Solar System in the near-term future, all of which have low ΔV with respect to Jupiter. I demonstrate that a spacecraft stationed near Jupiter would be well-positioned to rendezvous, orbit match, and accompany LD2 into the inner Solar System, providing an opportunity to observe the onset of intense activity in a pristine comet in situ.Anton Ermakov / Harriet Lau
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15-SepJasmeet K. Dhaliwal (in person)UC Santa CruzEarly Planetary Evolution: Insights from Siderophile ElementsThe siderophile elements are “iron-loving,” and strongly partition into metal phases (compared to silicate phases). In early solar system materials, the siderophile elements are strongly enriched in iron meteorites and metal components of other meteorite types, while they are significantly depleted in silicate phases of meteorites. The highly siderophile elements (HSE) are even more powerful tracers of early core-formation and metal-silicate differentiation in planetesimals. I will present siderophile abundance measurements in basaltic eucrite meteorites and compare them with data from stony-iron mesosiderites. For eucrites, the siderophiles record both primary metal-silicate differentiation and subsequent impact contamination. In the case of mesosiderites, siderophiles also lend insight into the core-crystallization history of the parent body. Bringing together geochemical measurements, experimental constraints and remote sensing data, I will demonstrate how siderophile elements are valuable for understanding planetary evolution on the different scales, between detailed laboratory work and space missions to asteroids.Sarah Arveson
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22-SepNick Choksi (in person)UC BerkeleyTesting Planet Formation from the Ultraviolet to the MillimeterThe Atacama Large Millimeter Array (ALMA) has revealed disks of gas and dust surrounding young stars to be ringed and gapped. Planets are suspected to reside within these gaps, by analogy to shepherd moons clearing gaps in planetary rings. What are these planets like? What are their masses and accretion rates? Are they done forming or are we catching them in the act? We answer these questions by combining ALMA molecular line and dust continuum data with simulations for how planets excavate gaps. We review the art of converting CO intensities into H2 gas densities, how planetary torques and disk viscosity compete to set gap widths and depths, and a simple Bondi theory for how a planet accretes gas from within a disk. Of the many planets speculated to be embedded within disks, two have been confirmed orbiting the star PDS 70 by direct imaging and spectroscopy. We discuss what their spectra, ranging from the millimeter through the ultraviolet, imply about planetary formation.Marta Bryan
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29-SepJ. J. Zanazzi (virtual)UTorontoThe Large Influence of Small Tilts on Protoplanetary Disks in Binary Star SystemsALMA has revealed an overwhelming number of highly warped protoplanetary disks, where the inner disk lies on an orbital plane highly misaligned to the outer disk. However, a prediction of tilted protoplanetary disk theories is even small misalignments can have a significant impact on the long-term inclination evolution of the disk. In this talk, we will go over the prediction and observational validation of theories regarding small tilts of protoplanetary disks in binary star systems. We will discuss why a protoplanetary disk orbiting two stars on an eccentric orbit can sometimes have its inclination grow to a 90 degree angle with the binary orbital plane, and the protoplanetary disks observed to lie in this “polar-aligned” state. We will examine how the gravitational torque on a protoplanetary disk from a binary companion can cause a planet to form around a backwards-spinning star, and how the spin directions of stars within numerous exoplanetary systems can be explained by this “disk torquing” mechanism. We will also discuss work on oddball protoplanetary disks, such as KH 15D, and ongoing observational efforts to further test the robustness of theories involving tilted protoplanetary disks in binary star systems.Marta Bryan
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6-OctJiayin Dong (virtual)Pennsylvania State UniversityTracing Dynamical Evolution of Planetary Systems: From Protoplanets to Young and Mature Planetary SystemsDynamical tracers of planets, such as their eccentricity, inclination, orbital obliquity, and spin rate, can be used to constrain and refine planet formation and evolution processes. I will begin the talk with mature planetary systems and show how the eccentricity and stellar obliquity of Warm Jupiters, giant planets with orbital periods of 8–200 days, can be used to constrain their origin channels. Using a catalog of Warm Jupiters discovered by TESS, we find Warm Jupiters are likely coming from multiple origin channels. I will then move on to younger planetary systems and discuss how debris disks can be used as a probe of young planetary system architectures. I will show if/how hidden planets could compromise our interpretation of the detected/assumed planet’s properties. In most system configurations, fortunately, the debris disk feature is dominated by a single planet. Lastly, I will talk about protoplanets and how giant planets accrete via their circumplanetary disks, reflecting on their spin rates. For a weakly magnetized planet, I will show the maximum spin rate the planet can reach is regulated by its circumplanetary disk’s boundary layer and the maximum value is only about 60–80% of the planet’s breakup rate, in contrast to the classical picture.Diogo Lourenço/Anton Ermakov
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13-OctYayaati Chachan (virtual)CaltechA Journey with Dust: From Protoplanetary Disks to Planetary Atmospheres and OutflowsDust in astronomy is often perceived as a hindrance to true characterization of celestial bodies. However, it is the humble dust particles that often run the show in planet formation and evolution. In this talk, I will present four different observationally inspired problems, which span a vast chronological range from core formation to atmospheric escape, and show how dust holds sway over them. I will begin by demonstrating that protoplanetary disks that are capable of forming giant planets are also capable of hosting super-Earths interior to the giant planet’s orbit, in line with the observed correlation between the occurrence rates of these two sub-populations. Next, I will show how dust dynamics and differences in grain properties across the water ice line create a region at intermediate distances where gas accretion is rapid. This might explain the preponderance of giant planets at such distances from their host stars, independently or complementarily to prevalent ideas on where massive cores form. Subsequently, since our understanding of the simultaneous accretion of dust and gas during planet formation remains poor, I will argue that atmospheric characterization of Neptune-class planets is valuable for advances in this area. In particular, I will discuss my efforts to characterize one such planet (HAT-P-11b) that, as a low metallicity Neptune, serves as an instructive challenge for formation models. Finally, I will substantiate the idea that dust in the form of photochemical hazes must be present in outflowing atmospheres of super-puffs (i.e. planets with super-Earth like masses but giant planet like radii) by using the transmission spectrum and bulk properties of the canonical super-puff Kepler-79d.Marta Bryan
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20-OctSabine Stanley (virtual)JHUSaturn’s Enigmatic DynamoCassini data have provided detailed characteristics of Saturn’s magnetic field. This includes the axisymmetric Gauss coefficients up to spherical harmonic degree 14, as well as bounds on the non-axisymmetric magnetic field components. In this talk I will discuss numerical dynamo simulations that attempt to reproduce the most ‘Saturn-like’ magnetic field possible. Although these models simplify some of the dynamics in Saturn’s dynamo region, they are able to reproduce many salient features of Saturn’s magnetic field, including its axisymmetry and dominant features of the magnetic power spectrum. Several observed magnetic features are dependent on properties of Saturn’s interior, including thermal anomalies and stable stratification at the top of the metallic hydrogen region. This suggests that we may be able to use magnetic field characteristics as a sort of tomography of Saturn’s deep interior.Anton Ermakov
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27-OctDayanthie Weeraratne (virtual)CSU NorthridgeLarge Low Velocities Provinces and Ultra-low Velocity Zones From Differentiation of the Earth’s CoreLarge low shear velocity provinces (LLSVP) are massive lower mantle structures observed today that may have a primordial origin. We propose a model that links Earth’s core formation to the growth of LLSVPs by impact melting and silicate entrainment to the outer core. Meteorite impacts during planetary accretion grew larger and more violent with time and may have melted the target surface and impactor creating magma reservoirs or magma oceans. Turbulent mixing may have emulsified the liquid metal which settled to form a metal pond. Previous studies (e.g. Fleck et al., 2018) show that this emulsified liquid metal pond may have formed diapirs which sink rapidly to the core. Numerical simulations of the extreme physical properties of liquid iron and silicates at finite length scales is prohibitive, therefore, we conduct laboratory fluid experiments using liquid metal gallium in glucose solutions. Metal settling is found to coat liquid metal drops with a film of viscous, low density fluid. Cases with emulsified metal, demonstrate the metal pond descends as a coherent Rayleigh−Taylor instability with a trailing fluid-filled conduit. Scaling to planetary interiors and high pressure mineral experiments indicates that molten silicates and volatiles are entrained to the iron core and initiate buoyant thermochemical plumes consistent with LLSVP’s that oxidize and hydrate the upper mantle. Experiments also indicate a textured layer forms during metal descent which is stable at the metal-fluid interface that is consistent with physical properties of the ULVZ observed at the core-mantle today.Sarah Arveson
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3-NovMelodie Kao (in person)UCSC
Brown Dwarf Radio Emission: A Window into Substellar Magnetospheres
Planetary magnetic fields influence atmospheric evaporation from space weather, yield insights into planet interiors, and are essential for producing aurorae. The most direct way of measuring magnetic fields on exoplanets and their brown dwarf cousins is by observing exo-aurorae at radio frequencies. Additionally, a quasi-stable and non-auroral quiescent radio component accompanies all known examples of substellar exo-aurorae and provides an alternative means for assessing the physics occurring in substellar magnetospheres. Low-frequency radio arrays will soon be sensitive to exoplanet radio emission and provide a new means of exoplanet detection and characterization. Now is a critical time to prepare for these upcoming searches by harnessing detailed studies of radio emission on observationally accessible exoplanet analogs: planetary-mass and cold brown dwarfs. I will synthesize the state of the art for brown dwarf magnetospheric radio studies, discuss implications for exoplanet magnetism, and highlight opportunities for the next generation of ground- and space-based radio facilities.Marta Bryan
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10-NovAmir Khan (virtual)ETH ZurichSeismology on MarsWith the deployment of a seismometer on the surface of Mars as part of NASA’s InSight mission, the Seismic Experiment for Interior Structure has been collecting continuous data since early 2019. The primary goal of InSight is to improve our understanding of the internal structure and dynamics of Mars, in particular of the crust, mantle, and core. Here I wish to describe our analysis of direct, reflected, and converted seismic body waves and what that tells us about the interior of Mars and possibly its formation.Anton Ermakov / Diogo Lourenço
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17-NovPaul Byrne (virtual)Washington University in St. LouisNew Insights Into the Geology of VenusWith three new Venus missions recently announced by NASA and ESA, attention is once more turning to the second planet. In the past few years, a view has emerged of a much more dynamic world than we once thought. In this talk, I'll present an overview of our current understanding of Venus, followed by insights from two recent studies I've left to understand the planet's past and present properties—which can be tested by those new missions.Diogo Lourenço
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24-NovNo seminar
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1-DecNatasha Batalha (virtual)NASA AmesThe Open Access Era of Exoplanet Characterization at the Onset of Next-Generation Telescopes One of NASA's primary goals is to observationally characterize exoplanet atmospheres, understand the chemical and physical processes of exoplanets and improve the understanding of the origins of exoplanetary systems. Throughout the next decade and beyond, JWST, Roman, future mission concepts, and ground based telescopes will work towards achieving these goals by interpreting a diverse set of exoplanet atmosphere observations, ranging from hot gas giants to small temperate rocky worlds. Our understanding and interpretation of this full gamut of spectroscopy data will hinge on our ability to accurately link observations to theoretical models. Therefore, it is imperative that our theoretical models are equipped to tackle these problems. Leading up to this new era in exoplanetary space science, one of our goals has been to ensure that the community is equipped with robust, user-friendly, open-source, theoretical models needed to both plan and execute ground-breaking science. Open access tools increase the accessibility of our science, the diversity of ideas, and naturally foster betters collaborations. I will first discuss the current landscape of theoretical exoplanet model development. Then, I will discuss our recent developments in cloud, opacity, and spectroscopy models that are working together to enable effective interpretation of exoplanet spectroscopy.Diogo Lourenço
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8-DecZack Geballe (virtual)Carnegie Inst. of ScienceLaboratory constraints on thermal conduction near Earth's core-mantle boundaryMany terawatts of heat conduct across Earth's core-mantle boundary (CMB), cooling the outer core from above and heating the mantle from below. This heat transfer helps drive mantle convection, and it might power the geodynamo. However, there are many open questions related to CMB heat transfer, including: How many terawatts of heat conduct across the CMB? What is the characteristic thickness of the thermal boundary layer in the lowermost mantle? What drives outer core convection today and in the past billion years? Popular estimates are "~100 km", "~12 TW", and "a combination of thermal and compositional buoyancy". To generate more accurate answers, we need more accurate knowledge of the properties of mantle and core materials, notably thermal conductivities and melting temperatures. In this talk, I will present the results of thermal conductivity measurements on silicates up to 120 GPa, and preliminary results on electrical conductivity and melting of iron up to 80 GPa using new laboratory methods. To conclude, I will make two pessimistic and one optimistic argument: (1) the popular estimates of electrical conductivity from Ohta et al. (2016) are erroneously high, (2) uncertainty in the melting temperature of iron alloys continues to be a major impediment to understanding core convection, and (3) new measurements using pulsed Joule heating in diamond anvil cells have great potential for improving the accuracy of both the electrical conductivity and melting temperature of iron alloys at the pressures of Earth's core.Sarah Arveson
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15-DecNo seminar - AGU
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