Water Delivery and Giant Impacts in the 'Grand Tack' Scenario

A new model for terrestrial planet formation (Hansen 2009, Walsh et al. 2011) has explored accretion in a truncated protoplanetary disk, and found that such a configuration is able to reproduce the distribution of mass among the planets in the Solar System, especially the Earth/Mars mass ratio, which earlier simulations have generally not been able to match. Walsh et al. tested a possible mechanism to truncate the disk--a two-stage, inward-then-outward migration of Jupiter and Saturn, as found in numerous hydrodynamical simulations of giant planet formation. In addition to truncating the disk and producing a more realistic Earth/Mars mass ratio, the migration of the giant planets also populates the asteroid belt with two distinct populations of bodies--the inner belt is filled by bodies originating inside of 3 AU, and the outer belt is filled with bodies originating from between and beyond the giant planets (which are hereafter referred to as `primitive' bodies). We find here that the planets will accrete on order 1-2% of their total mass from primitive planetesimals scattered onto planet-crossing orbits during the formation of the planets. For an assumed value of 10% for the water mass fraction of the primitive planetesimals, this model delivers a total amount of water comparable to that estimated to be on the Earth today. While the radial distribution of the planetary masses and the dynamical excitation of their orbits are a good match to the observed system, we find that the last giant impact is typically earlier than 20 Myr, and a substantial amount of mass is accreted after that event. However, 5 of the 27 planets larger than half an Earth mass formed in all simulations do experience large late impacts and subsequent accretion consistent with the dating of the Moon-forming impact and the estimated amount of mass accreted by Earth following that event

LMC X-1: A New Spectral Analysis of the O-star in the binary and surrounding nebula

We provide new observations of the LMC X-1 O star and its extended nebula structure using spectroscopic data from VLT/UVES as well as H$\alpha$ imaging from the Wide Field Imager on the Max Planck Gesellschaft / European Southern Observatory 2.2m telescope and ATCA imaging of the 2.1 GHz radio continuum. This nebula is one of the few known to be energized by an X-ray binary. We use a new spectrum extraction technique that is superior to other methods to obtain both radial velocities and fluxes. This provides an updated spatial velocity of $\simeq 21.0~\pm~4.8$ km s$^{-1}$ for the O star. The slit encompasses both the photo-ionized and shock-ionized regions of the nebula. The imaging shows a clear arc-like structure reminiscent of a wind bow shock in between the ionization cone and shock-ionized nebula. The observed structure can be fit well by the parabolic shape of a wind bow shock. If an interpretation of a wind bow shock system is valid, we investigate the N159-O1 star cluster as a potential parent of the system, suggesting a progenitor mass of $\sim 60$ M$_{\odot}$ for the black hole. We further note that the radio emission could be non-thermal emission from the wind bow shock, or synchrotron emission associated with the jet inflated nebula. For both wind and jet-powered origins, this would represent one of the first radio detections of such a structure.Comment: 7 Figures, 4 Table

Determination of Optical Constants for Titan Aerosol-, and Exoplanet and Brown Dwarf Cloud Particle Analogs from the Visible to the Far Infrared

Here we present optical constants covering a broad wavelength range, from the visible to the far infrared, for Titan aerosol analogs produced in the Titan Haze Simulation (THS) experiment at Ames COSmIC facility, as well as other exoplanet-relevant materials

Implications of ocean acidification for marine microorganisms from the free-living to the host-associated

Anthropogenic CO2 emissions are causing oceans to become more acidic, with consequences for all marine life including microorganisms. Studies reveal that from the microbes that occupy the open ocean to those intimately associated with their invertebrate hosts changing ocean chemistry will alter the critical functions of these important organisms. Our current understanding indicates that bacterial communities associated with their host will shift as pH drops by another 0.2–0.4 units over the next 100 years. It is unclear what impacts this will have for host health, however, increased vulnerability to disease seems likely for those associated with reef corals. Natural CO2 seeps have provided a unique setting for the study of microbial communities under OA in situ, where shifts in the bacterial communities associated with corals at the seep are correlated with a decline in abundance of the associated coral species. Changes to global biogeochemical cycles also appear likely as photosynthesis and nitrogen fixation by pelagic microbes becomes enhanced under low pH conditions. However, recent long-term studies have shown that pelagic microbes are also capable of evolutionary adaptation, with some physiological responses to a decline in pH restored after hundreds of generations at high pCO2 levels. The impacts of ocean acidification (OA) also will not work in isolation, thus synergistic interactions with other potential stressors, such as rising seawater temperatures, will likely exacerbate the microbial response to OA. This review discusses our existing understanding of the impacts of OA on both pelagic and host-associated marine microbial communities, whilst highlighting the importance of controlled laboratory studies and in situ experiments, to fill the current gaps in our knowledge

Why Humans Do What They Do: Interdisciplinary Research on Decision Making at the University of Missouri

Comparative Medicine - OneHealth and Comparative Medicine Poster SessionMU has enormous potential to be the site of path-breaking interdisciplinary research on the topic of realistic decision making. Not only is this research a basic component of human life science, it also has clear application to the marketing of life-science-related industries and products. The standard approach to modeling decision making incorporates a variety of simplifying assumptions. Agents are often assumed to be fully rational and to have narrowly defined personal goals, complete knowledge about the relevant options, and the ability to perform complex optimization calculations. Although these assumptions are frequently relaxed, standard psychological and economic analyses derive power from the ability of simplified models to represent complex behaviors. Despite the benefits of assuming a simplified rational decision-making process, there is growing recognition that alternative models, which replace the assumption of simple rationality with alternative assumptions, may aid in understanding decision making. As we better understand how humans make decisions in the real world, significant changes will be felt across economics, business, politics, and ethics. Economists have long understood that groups of individuals will not always coordinate on efficient outcomes merely by following self interest. But recently they have focused attention on the basic decision-making process, reflecting an increasingly mainstream acceptance of models in which simple rational decisions are no longer assumed. This is attested to by the number of popular trade books and new celebrity intellectuals who have attracted unprecedented attention to this kind of research; for example, Malcolm Gladwell's popular trade book, Blink: The Power of Thinking without Thinking (2005), focuses on how humans make immediate judgments through unconscious mechanisms that operate independently of rational decision making. A better understanding of the nonrational factors that influence decision making will have specific, transformational consequences for large areas of our economic and political lives. Even though such research is still in its infancy, there are already several private consulting firms that work with Fortune-100 companies for the purpose of informing their marketing and sales strategies through the use of neurological studies. In the political arena, the same companies are now marketing their services to political parties for the purpose of influencing voters' reactions to candidates and platforms. As this research proceeds, we can easily envision a future in which a focus on the nonrational elements of decision making becomes even more dominant among those who move public opinion. MU is in a unique position to carry out the kind of interdisciplinary research—based on a framework that goes beyond the traditional assumptions still largely dominant in rational-choice models—that is at the center of recent developments in the study of decision-making; indeed, we have an exceptional opportunity to become an important center for such research. The reason for this is the broad and deep research overlap among faculty in economics, psychology, philosophy, and anthropology, together with MU's new, state-of-the-art Brain Imaging Center. A survey of faculty research interests in the four disciplines shows that there are obvious strengths in the study of decision making that cannot be duplicated elsewhere

What are the attributes of good pharmacy faculty (lecturers)? An international comparison of the views of pharmacy undergraduate students from universities in Australia and Wales, UK

This study aimed to investigate what La Trobe pharmacy students (Australia) considered to be the attributes of a good lecturer (faculty member) and to compare the findings to pharmacy undergraduates at Cardiff University, Wales, UK. A 22 item questionnaire, developed at Cardiff, was administered to students at La Trobe University. Data were analysed using descriptive statistics, and Mann-Whitney U Test or Kruskal-Wallis Test were used to compare groups. Ethics approval was obtained. Pharmacy students believed good lecturers (faculty) provided clear instruction and assessment criteria, were enthusiastic, inspired students to do their best, motivated students to learn, were accessible for support and started the teaching sessions on time. They also provided timely feedback and illustrated the relevance of material to pharmacy. Australian and UK pharmacy undergraduates in this study shared the same opinions on most aspects of the positive attributes of faculty (lecturers)

A low mass for Mars from Jupiter's early gas-driven migration

Jupiter and Saturn formed in a few million years (Haisch et al. 2001) from a gas-dominated protoplanetary disk, and were susceptible to gas-driven migration of their orbits on timescales of only ~100,000 years (Armitage 2007). Hydrodynamic simulations show that these giant planets can undergo a two-stage, inward-then-outward, migration (Masset & Snellgrove 2001, Morbidelli & Crida 2007, Pierens & Nelson 2008). The terrestrial planets finished accreting much later (Klein et al. 2009), and their characteristics, including Mars' small mass, are best reproduced by starting from a planetesimal disk with an outer edge at about one astronomical unit from the Sun (Wetherill 1978, Hansen 2009) (1 AU is the Earth-Sun distance). Here we report simulations of the early Solar System that show how the inward migration of Jupiter to 1.5 AU, and its subsequent outward migration, lead to a planetesimal disk truncated at 1 AU; the terrestrial planets then form from this disk over the next 30-50 million years, with an Earth/Mars mass ratio consistent with observations. Scattering by Jupiter initially empties but then repopulates the asteroid belt, with inner-belt bodies originating between 1 and 3 AU and outer-belt bodies originating between and beyond the giant planets. This explains the significant compositional differences across the asteroid belt. The key aspect missing from previous models of terrestrial planet formation is the substantial radial migration of the giant planets, which suggests that their behaviour is more similar to that inferred for extrasolar planets than previously thought.Comment: 12 pages, 4 figures + Supplementary Material 46 pages, 10 figure