CIPS seminar spring 2017 (public)
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CIPS SEMINARS - Spring 2017
131 Campbell Hall
Wednesdays 3:10 - 4:00 pm
18-Janno seminar
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
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
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
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
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
1-MarDan WerthimerSETI and Breakthrough ListenCan we detect radio, infrared, or optical signals from other civilizations?
Current and future SETI projects, including the new $100-million Breakthrough Prize Foundation Listen project, may provide an answer.
Dan will describe the rationale for past and future searches and will show how new technologies and telescopes are revolutionizing SETI.
Burkhard Militzer
8-MarMike Wong (UCB Astronomy)Molecular Clouds in Extragalactic EnvironmentsOne of the key unknowns in our study of galaxy evolution is the puzzle of how the star formation rate is dictated by the physical state of the interstellar medium (ISM). In this talk I discuss how progress in characterizing molecular cloud populations in external galaxies - a field largely pioneered by Berkeley astronomers - has contributed to our understanding of star formation. I will focus on the nearest star-forming galaxy, the Large Magellanic Cloud, for which a fairly complete census of GMCs exists, and highlight the important role of ALMA observations in uncovering the internal structures of GMCs in different environments.Leo Blitz
15-MarJing Luan (UCB Astronomy)What accounts for Saturn’s tidal Q? A question possibly answerable by Cassini.The tidal quality factor, Q, is a parameter describing the efficiency of tidal dissipation. The Q of a giant planet is important in understanding of the orbital evolutions of its natural satellites and short-period exo giant planets, e.g. hot Jupiters. Astrometry study of Saturn’s natural satellites constrain its Q ~1800. Resonance lock between the satellite and an internal oscillation mode/wave of Saturn could match this constraint naturally. However, it does not answer the question which kind of mode/wave is locked with each satellite. The candidates include gravity mode and inertial wave. Although they could result in the same observed tidal Q for Saturn, they create very different perturbations to the gravity field of Saturn. Later this year, Cassini, will orbit all the way to the surface of Saturn, and measure its gravity field. The high accuracy of Cassini’s measurement will probably distinguish gravity mode and inertial wave. Furthermore, it will help reveal more information about the interior of Saturn.
22-MarSteven Beckwith (UCB Astronomy)"Why Is There Life?""Are We Alone?" is an old question that has been given new immediacy with the discovery that Earth-like planets are common in the Galaxy. Yet life is an emergent property that we cannot predict from the laws of physics and chemistry, and we do not know how the early Earth made the jump from chemistry to biology. This talk will discuss the outstanding challenges we have to figure out why life exists and whether it is common or rare on other planets.
29-MarSpring Break - No Seminar
5-AprSivan Ginzburg (Hebrew University)Tidal Interactions of Short-period PlanetsI will present two roles that tides may play in shaping the observed short-period planet population. First, I will discuss the in-spiral and Roche-lobe overflow of hot Jupiters due to the tides that they raise on their hosts stars. The expected fate of these doomed planets, combined with the observed population, provides useful constraints on their structure and formation. Next, if time permits, I will investigate how tidal heating inside a young super-Earth restricts it from accreting a voluminous gas envelope. This effect may shape the population of puffy super-Earths, which seem to be abundant in the Kepler results.Eugene Chiang
12-AprKim Bott (University of Washington)Polarimetry for biosignatures and habitability markersPolarimetry provides unique information about planetary atmospheres and surface properties complementing more conventional observations. However, polarimetry is currently an under-utilized technique for exoplanet characterization, especially for smaller planets, where its utility is poorly understood. Models of polarised light from terrestrial planets can allow for the detection of biosignatures and habitability markers. Combining the abilities of the Virtual Planetary Laboratory's SMART radiative transfer code (glint capabilities from a Cox-Munk Formalism [1]) and the University of New South Wales' VSTAR radiative transfer code (polarimetric capabilities) we explore the detectability of ocean glint for an Earth-like planet in polarised light. This is compared to theory (e.g. [2] [3] [4]) and assessed in observational contexts.Imke de Pater
19-AprSean Wahl (EPS, UCB)Jupiter's Interior and Juno Gravity MeasurementsThe Juno spacecraft mission to Jupiter offers our best chance yet to probe the deep interior of a gas giant planet. Meanwhile, recent first-principles simulations on hydrogen-helium mixtures allow for the construction of realistic interior models. Juno's arrival at Jupiter motivates development of a more precise method for calculating a model gravitational field to match high-precision measurements. The concentric Maclaurin spheroid (CMS) method achieves this with a non-perturbative, self-consistent calculation of the shape and gravitational field of a rotating liquid body. Using this method I predict the tidal responses of Jupiter and Saturn, which exhibit a number of unexpected features attributed to the planet's rapid rotation. I also present a preliminary study interpreting the gravitational moments measured by Juno during its first two perijoves. On the basis of this modeling, there remain inconsistencies in either our knowledge of Jupiter's interior structure, or the hydrogen-helium equation of state. One exciting possibility is that Jupiter's core has been diluted and expanded to a significant portion of the planet, which would have important consequences for formation and evolution of Jupiter and other giant planets. Juno will continue to contribute to our understanding of Jupiter’s interior through refinement of the gravity measurements and other observations.Burkhard Militzer
26-AprAndrew Westphal (SSL, Physics, UCB)The Future of Stardust ResearchOver 99% of the small bodies in the Solar System reside in its outer reaches – in the Kuiper Belt and Oort Cloud.  Kuiper Belt bodies are probably the best preserved representatives of the icy planetesimals that dominated the bulk of the solid mass in the early Solar System.  They likely contain preserved materials inherited from the protosolar cloud, held in cryogenic storage since the formation of the Solar System.  Despite their importance, they are relatively underrepresented in our extraterrestrial sample collections by many orders of magnitude (~1013 by mass) as compared with the asteroids, represented by meteorites, which are composed of materials that have generally been strongly altered by thermal and aqueous processes.  We have only begun to scratch the surface in understanding Kuiper Belt objects, but it is already clear that the very limited samples of them that we have in our laboratories hold the promise of dramatically expanding our understanding of the formation of the Solar System.   Stardust returned the first samples from a known small solar-system body, the Jupiter-family comet Wild 2, and, in a separate collector, the first solid samples from the local interstellar medium.   The first decade of Stardust research resulted in over 142 peer-reviewed publications, including 15 papers in Science.  Analyses of these amazing samples continue to yield unexpected discoveries and to raise new questions about the history of the early Solar System.  We identify 9 high-priority scientific objectives for future Stardust analyses that address important unsolved problems in Planetary Science, all of which can be addressed in the laboratory.Burkhard Militzer
3-MayEve Lee (Astronomy, UCB)The Late-time Formation and Dynamical Signatures of Small PlanetsAt short orbital periods (less than ~100 days), Earths and Super-Earths (collectively sub-Neptunes) are the most common. In this talk, I will demonstrate how the late-time, in-situ formation can explain their three basic observables: the distributions of orbital periods, masses, and radii. Sub-Neptunes around FGKM dwarfs are evenly distributed in log orbital period down to ~10 days, but dwindle in number at shorter periods. I will demonstrate that both the break at ~10 days and the slope of the occurrence rate down to ~1 day can be reproduced if planets form in-situ in disks that are truncated by their host star magnetospheres at co-rotation. Planets can be brought from disk edges to ultra-short (<1 day) periods by asynchronous equilibrium tides raised on their stars. To explain both their radii and masses, sub-Neptunes must have 0.1--10% by mass gaseous atmospheres. I will demonstrate how the late-time formation in a gas-depleted nebula can naturally explain these atmospheric mass fractions. In fact, sub-Neptune cores likely form in a nebula that is so heavily depleted in gas that once they form, they will hardly migrate. Eugene Chiang
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