Winter 2014

Winter 2014

Tuesday Afternoons at 4:00 PM
Natural Science Annex 101

January 14, 2014

Steven Stanley, University of Hawaii

Relation of Phanerozoic stable isotope excursions to climate, bacterial metabolism, and major extinctions

Hosts: Jim Zachos/Dan Killam

January 21, 2014

James Rae, Cal Tech University

Deglacial CO2 rise via deepwater formation in the North Pacific and Southern Oceans: new insights from boron isotopes and radiocarbon

Hosts: Jim Zachos/Dustin Harper

January 28, 2014

Jonathan Mitchell, University of California, Los Angeles

How the west winds won on Titan and Venus

Atmospheric superrotation occurs when westerly winds prevail over the equator, so that the atmosphere spins faster than the planetary surface. Although not a climatological phenomenon on Earth, superrotation persists on Venus, Titan, Jupiter and Saturn, making it a relatively common phenomenon in the Solar System. I will characterize the mechanisms giving rise to the spontaneous generation of superrotation in idealized global simulations with no diurnal cycle, radiation or convection. The mechanism involves an new fluid instability that couples a fast moving equatorial Kelvin (gravity) wave with slow moving Rossby waves experiencing a significant Doppler shift from a strong westerly jet at higher latitudes. I will discuss the planetary regimes favorable to the development of superrotation by this instability, and place the climates of Earth, Mars and Titan in this context.

Hosts: Francis Nimmo/Doug Hemingway


WEDNESDAY January 29, 2014, EMS A340 11:30 a.m. - 12:30 p.m.

Jonathan Mitchell, University of California, Los Angeles

Monsoons and the ITCZ during LGM and on Titan

Tropical precipitation on Earth is dominated by the Inter­tropical Convergence Zone (ITCZ). The seasonal cycle of the ITCZ is punctuated by abrupt transitions over land called the monsoon. Through a novel combination of geochemical proxies and model simulations, we show an enhanced sensitivity of the East Asian Monsoon (EAM) relative to the global signal during the Last Glacial Maximum (LGM) is the result of a strong stationary wave response of the midlatitude jet stream to the presence of the ice sheets, with potentially important implications for climate sensitivity predictions from GCMs.

Like Earth’s tropics, Titan's precipitation is dominated by an ITCZ, except that at solstices Titan's ITCZ travels to very high latitudes. Observations of Titan’s methane clouds confirm this picture of a highly seasonal ITCZ.  I will describe how these and other factors give rise to precipitation events that are dramatically more intense than had been expected.

Model simulations suggest that while Titan's ITCZ shows significant seasonality, it lacks abrupt monsoon­like transitions prevalent on Earth. To connect Titan’s seasonal ITCZ and Earth’s monsoon, I will briefly discuss aquaplanet GCM simulations (designed for Earth) of varying radius and rotation rate, with the goal of illuminating processes that inhibit the poleward extent and abruptness of the summer Monsoon/ITCZ.

Host: Francis Nimmo

February 4, 2014

Joseph Michalski, Planetary Science Institute

Did Mars ever have a lively underground scene? New perspectives on the habitability of the Martian subsurface

By the time eukaryotic life or photosynthesis evolved on Earth, the martian surface had become extremely inhospitable – cold, hyperarid, acidic, oxidizing and bathed in UV radiation. But, the subsurface of Mars could potentially have contained a vast microbial biosphere. Data from recent missions have revealed spectacular views of materials exhumed from the subsurface by impact craters. These include carbonates and complex, mixed-layer clays of probable hydrothermal origins. In this talk, I evaluate new evidence suggesting that the subsurface is, and has likely always been, the most habitable part of Mars. I describe a clear vision for how the Mars 2020 mission or other sample-return missions can access materials that contain a record of subsurface chemical processes.

Hosts: Noah Finnegan


WEDNESDAY February 5, 2014, EMS A340 11:30 a.m. - 12:30 p.m.

Joseph Michalski, Planetary Science Institute

Volcanic outgassing, sulfur sequestration, and low-temperature chemical weathering on Mars

Volcanic outgassing on early Mars would have strongly affected the ancient climate, and ultimately, controlled the volatile inventory of the planet. Various theoretical estimates of the amount of Noachian (>3.6 Ga) volcanic outgassing span orders of magnitude, and these values are difficult to empirically constrain because little is known about ancient volcanism on Mars. This may be because ancient volcanic provinces were all removed by erosion, or it might be that the most ancient volcanoes were of fundamentally different character than that of the well known, younger shield volcanic provinces. Here, I present evidence that a category of ancient, explosive volcanoes has until now gone unnoticed. These structures, termed plains-style caldera complexes, formed through massive, explosive eruptions – similar in style to those of supervolcanoes on Earth. A number of potential supervolcanoes have been identified in Arabia Terra – a terrain never before linked to volcanism. It is likely that more unrecognized, explosive calderas are present throughout the ancient crust. Understanding of these features will help fill a major gap in our knowledge of early processes of crust formation and outgassing. Regardless of eruptive style, all ancient volcanoes on Mars would have erupted significant amounts of sulfur, water, and ash into the atmosphere. What was the fate of these materials? On Earth, the ocean serves as a major sink for sediments and a buffer to surface chemistry. But on Mars, the ash, sulfur and water vapor (snow) were likely deposited together in air-fall sedimentary deposits on an arid landscape. I will present a model for how these deposits might have been chemically weathered at low temperatures, leading to the formation of layered sulfate deposits observed today.

Host: Noah Finnegan

February 11, 2014

Matija Cuk, SETI Institute

Moons of Saturn: Young or Old?

Saturn has eight major moons which orbit close to Saturn's equatorial plane, indicating formation from a circumplanetary ring or disk. Despite decades of effort, many characteristics of the moons' orbits have not been explained using approaches that assume that all the major satellites are as old as the planet. Lainey et al.(2012) re-analized observed positions of Saturn's moons over the last century, and found that the tidal response of Saturn is an order of magnitude stronger than previously thought. This result is highly controversial, but it imediately solves the problem of excessive tidal heating of Enceladus. However, if the results of Lainey et al.(2012) are correct, most of Saturn's mid-sized moons cannot be primordial, and must have re-accreted within the last billion years from fragments of a previous generation of satellites. I will discuss how faster tidal evolution of Saturn's moons can account for many unexplained aspects of the system, and propose ways to test this hypothesis.

Hosts: Pascale Garaud


WEDNESDAY February 12, 2014, EMS A340 11:30 a.m. - 12:30 p.m.

Matija Cuk, SETI Institute

Dynamics of Small Bodies in the Inner Solar System

In this talk I will present results of two separate projects: delivery of meteorites from the Hungaria asteroid family, and the long-term dynamics of Mars Trojans. In the first part, using direct orbital integrations, I will show that the E-type Hungaria asteroid family interior to the main asteroid belt is the most likely source of aubrite meteorites. Aubrites (enstatite achondrites) are often thought to originate on high-albedo E-type asteroids, which also dominate the Hungaria family. As a group, aubrites also have the longest cosmic ray exposure (CRE) ages of all stony meteorites, which I find to be a signature of their non-resonant delivery mechanism from the Hungarias. In the second part, I will discuss the history of the Eureka cluster, a dynamical grouping that includes the majority of known Trojan asteroids of Mars. I will show that the inclination and libration amplitude distribution of the Eureka cluster members can be explained by Yarkovsky (i.e., thermal radiation powered) drift starting from the orbit of the largest member. Finally, I will discuss the nature and the age of the cluster, as well as wider implicatins for orbital and rotational dynamics of small asteroids in the absence of mutual collisions.

Host: Pascale Garaud/Doug Hemingway

February 18, 2014

Kevin Walsh, Southwest Research Institute

The Grand Tack: Jupiter's migration to 1.5 AU, and how it shaped the inner solar system

A persistent difficulty in terrestrial planet formation models is creating Mars analogs with the appropriate mass: Mars is typically an order of magnitude too large in simulations. A recent study found that a small Mars can be created if the planetesimal disk from which the planets form has an outermost edge at 1.0 AU. However, that work and no previous work, can explain such a truncation of the planetesimal disk and preserve the asteroid belt. We show that gas-driven migration of Jupiter inward to 1.5 AU, before its subsequent outward migration, can truncate the planetesimal disk and repopulate the asteroid belt. The same process that scatters material into the Asteroid Belt also sends primitive asteroids onto orbits that cross the still-forming terrestrial planets, providing a mechanism to deliver water-rich material throughout the accretion of the Earth. This dramatic migration history of Jupiter suggests that the dynamical behavior of our giant planets, characterized by dramatic radial migration, was more similar to that inferred for extra-solar planets than previously thought.

Hosts: Ian Garrick-Bethell/Doug Hemingway


WEDNESDAY February 19, 2014, EMS A340 11:30 a.m. - 12:30 p.m.

Kevin Walsh, Southwest Research Institute

Asteroid Dynamics and Geology - Origin of near-Earth Asteroids

Multiple space missions are headed off to return samples from near-Earth Asteroids. However, near-Earth Asteroids are a transient population with their population being constantly re-plenished with
bodies from the Main Asteroid belt. The Main Asteroid belt is a big place with lots of diversity and all regions and asteroid types can make the trip to become near-Earth Asteroids. Therefore, context for a returned sample requires connecting a specific near-Earth Asteroid with a region in the Main Asteroid Belt or ideally a specific family of asteroids. However, the dynamical evolution of asteroids from the Main Belt to the near-Earth population requires asteroids to drift due to a radiation effect, which itself depends on the shape and surface properties of the asteroid. This is complicated by the ability of small asteroids to reshape due to rotation rate changes brought about by related, but different, radiation effects. This intersection of asteroid dynamics and geology is critical for understanding the evolution of the asteroid belt and the delivery of near-Earth Asteroids over time. I will discuss a hunt for the source region of a space mission target asteroid, why that led to the discovery of a new asteroid family and how the reshaping of km-sized asteroids is the critical physics in understanding which is the actual parent family.

Host: Ian Garrick-Bethell

February 25, 2014

Xi Zhang, Lunar and Planetary Laboratory, University of Arizona

The Atmosphere of Jupiter: Insights from Cassini Observations

In December 2000, the Cassini spacecraft flew past Jupiter en route to Saturn. During the months-long Jupiter flyby, a wealth of information was obtained. In this presentation, I will show how Cassini observations have significantly changed our understanding of Jupiter’s middle atmosphere. We derived spatial maps of temperature and hydrocarbon tracers from the Cassini infrared spectra. The results provide definitive evidence of the long-hypothesized large-scale meridional circulation in the stratosphere of Jupiter. From the Cassini images, we deduced the fractal nature of the particles in the middle and high latitudes. Detailed analysis reveals that the energy balance of Jupiter’s stratosphere is not controlled by the gas components as previous work assumed, but more likely controlled by the aerosols produced by the atmospheric photochemistry and ion-chemistry. Combining the unprecedented observations with the state-of-art radiative, chemistry-transport and dynamical models, we have pieced together a complete picture of how atmospheric dynamics, chemistry, and radiation are coupled to shape the climate of the middle atmosphere of Jupiter.

Hosts: Jonathan Fortney/Doug Hemingway


WEDNESDAY February 26, 2014, EMS A340 11:30 a.m. - 12:30 p.m.

Xi Zhang, Lunar and Planetary Laboratory, University of Arizona

Venus: the Sulfur Factory Unveiled

Venus atmosphere is nature’s laboratory of sulfur chemistry. The parent species of sulfur, carbonyl sulfide (OCS) and sulfur dioxide (SO2), are produced in the lower atmosphere via surface chemistry and volcanoes and subsequently transported upward to the middle atmosphere, where they undergo photochemical processing and eventually condense as sulfuric acid cloud and elemental sulfur aerosols. Several striking discoveries from Venus Express since 2006 have greatly challenged our current picture of atmospheric chemistry and circulation on Venus. The unexpected SO2 layer in the upper atmosphere requires a sulfur source that is likely to be provided by aerosols. I will present a solution to this problem by including the solar-to-anti-solar circulation and gas-aerosol conversion that was missing in previous models. I will also briefly discuss other challenges and possible interpretations related to the sulfur cycle, such as the bimodal distribution of the aerosols, the unknown UV absorber in the clouds and the large-amplitude variability of SO2 in hourly to decadal timescales above the cloud tops.

Host: Jonathan Fortney

March 4, 2014

Francis Nimmo, University of California, Santa Cruz

Looking inside moons using gravity and topography

Host: TBA

March 11, 2014

Hans-Jürgen Brumsack, Institut für Chemie und Biologie des Meeres (ICBM)

A geochemical comparison of the Eemian and Holocene marine ingressions into the Black Sea

Host: Adina Paytan