CIPS seminar spring 2017 (public)
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CIPS SEMINARS - Spring 2017
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131 Campbell Hall
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Wednesdays 3:10 - 4:00 pm
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DateSpeakerTitleAbstractHost
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18-Janno seminar
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25-JanDaniel Stolper (EPS, UCB)Reconstructions of atmospheric O2 concentrations over earth's history: A case study of the past million yearsEarth's elevated partial pressure of O2 (0.2 atm) is critical in maintaining a diverse array of organisms and geochemical reactions on the earth’s surface. The biological origin of O2 in the atmosphere has led to the proposed use of O2 as a ‘biomarker’ for life beyond earth. First I will review the current understanding earth's history of atmospheric oxygen concentrations. Second, I will use measurements of O2 concentrations in ice cores to develop a new, direct record of atmospheric O2 concentrations over the past million years. This record indicates O2 has been dealing at a rate of ~1% per million years over this time frame. I will discuss plausible geochemical reasons for this decline.Burkhard Militzer
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1-FebBruce Buffett (EPS, UCB)Unsound Methods of Probing Earth’s CoreConvection in Earth’s core generates long-period magnetic waves when the top of the core is thermally stratified. We detect these waves using magnetic-field observations and recover quantitative estimates for the stratification. A description of the waves and wave generation has some similarities to acoustic-wave generation in stars, although the largest source of excitation is probably due to buoyant parcels rising into the stratified layer. The influence of Reynolds and Maxwell stresses are expected to be smaller. Numerical dynamo models suggest that convection preferentially excites symmetric waves about the equator, which is compatible with the observations. Estimates of the strength and thickness of thermal stratification imposes tight constraints on the thermal evolution of the core.Burkhard Militzer
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8-FebJames Owen (IAS)Sculpting exoplanets through evaporationThe Kepler mission has transformed our knowledge of the properties of extra-solar planets. It has told us a dominant - perhaps the dominant - population of exoplanets are those close to their parent stars with masses in the range 1-20 M⊕. Unlike the low-mass, close-in planets in our solar system these exoplanets are thought to contain voluminous H/He envelopes. I will discuss the evolution of this population of exoplanets, particularly with regard to mass-loss. It appears that as soon as these planets finish forming, and their parent disc disperses they begin a lifelong period of mass-loss and evaporation which imprints itself on the population we see today.Eve Lee
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15-Feb Matija Cuk (SETI)Tidal evolution of the Moon from a high-obliquity, high-angular-momentum EarthIn the giant-impact hypothesis for lunar origin, the Moon accreted from an equatorial circum-terrestrial disk; however, the current lunar orbital inclination of five degrees requires a subsequent dynamical process that is still unclear. In addition, the giant-impact theory has been challenged by the Moon’s unexpectedly Earth-like isotopic composition. Here we show that tidal dissipation due to lunar obliquity was an important effect during the Moon’s tidal evolution, and the lunar inclination in the past must have been very large, defying theoretical explanations. We present a tidal evolution model starting with the Moon in an equatorial orbit around an initially fast-spinning, high-obliquity Earth, which is a probable outcome of giant impacts. Using numerical modelling, we show that the solar perturbations on the Moon’s orbit naturally induce a large lunar inclination and remove angular momentum from the Earth-Moon system. Our tidal evolution model supports recent high-angular-momentum, giant-impact scenarios to explain the Moon’s isotopic composition and provides a new pathway to reach Earth’s climatically favourable low obliquity.Eugene Chiang
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22-FebPhil Nicholson (Cornell)Kronoseismology: Probing Saturn’s interior via its rings.In previous work (Hedman & Nicholson [2013] Astron. J. 146, 12; Ibid [2014] MNRAS 444, 1369) we have identified several inward-propagating density waves in Saturn's C ring with outer Lindblad resonances (OLRs) generated by internal oscillations in Saturn. The oscillations involved are sectoral f-modes (ie., fundamental modes with l = m) with m = 1, 2, 3, 4 and 10, as originally discussed by Marley & Porco [1993]. In addition, five outward-propagating waves between radii of 84,800 and 86,600 km have been identified as density waves driven by 3:2 tesseral resonances with fixed gravitational anomalies within the planet. I will present stellar occultation data for six additional waves from the catalog of Baillie et al. [2011], which are both weaker and shorter in wavelength than the previously-identified waves. We use a modified version of our wavelet-based technique to coadd phase-corrected spectra from multiple occultations, using trial values of `m` and the pattern speed to predict their relative phases. This enables us to detect waves too weak to see in individual data sets. Two of the new waves appear to be due to additional saturnian f-modes with m = 2 and m = 9. The other four waves appear to be in a new class: outward-propagating bending waves driven at outer vertical resonances (OVRs) with asymmetric Saturn internal oscillations for which l = m + 1. We identify four such waves with m = 4, 7, 8 & 9. All of the newly-identified waves are at radii less than 77,000 km. Only the m = 4 wave is near the location predicted by Marley & Porco [1993].Jing Luan
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1-MarDan WerthimerSETI and Breakthrough ListenBurkhard Militzer
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8-Mar
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15-Mar
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22-Mar
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29-Marspring break - no seminar
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5-AprSivan Ginzburg (Hebrew University)Eugene Chiang
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12-AprKim Bott (University of Washington)Imke de Pater
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19-AprSean Wahl (EPS, UCB)Jupiter's Interior and Juno Gravity MeasurementsBurkhard Militzer
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26-AprAndrew Westphal (SSL, Physics, UCB)The Future of Stardust ResearchBurkhard Militzer
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3-MayEve Lee (Astronomy, UCB)Eugene Chiang
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