Organiser and discussion leader
Professor David Stevenson FRS, Caltech, USA
Show speakers
Professor David Stevenson FRS, Caltech, USA
Professor David Stevenson FRS, Caltech, USA
David Stevenson is the Marvin L. Goldberger Professor of Planetary Science at the California Institute of Technology and is an Andrew D. White Professor-at-Large at Cornell University. A native of New Zealand, his early work was in the condensed matter physics of planetary interiors, especially giant planets, but his wide ranging career has included contributions to the interpretation of planetary magnetic fields, the formation of planetary cores, melt migration, the origin of the Moon and numerous aspects of planetary and satellite formation, evolution and structure. He was involved in the Cassini mission and is a Co-Investigator and group leader in the Juno mission, currently in orbit at Jupiter. Awards include Fellowship in the Royal Society (London), membership of the National Academy of Sciences (USA), the Urey Prize (American Astronomical Society) and Hess Medal (American Geophysical Union).
Giant impact origin of the moon- forty years on
Dr William Hartmann, Planetary Science Institute, USA
Abstract
Inspirations for the first presentations of the modern giant impact theory of the origin of the moon included discovery of the Orientale impact basin (Hartmann & Kuiper, 1962) and study of the work of Safronov in the later 1960s, as well as failure of the three primary lunar origin theories in vogue during the Apollo era. This raised questions about the largest impactors to hit Earth during its accretion. The work was presented by Hartmann and Davis in 1974 (Cornell satellite conference) and 1975 (Icarus paper). Discovery of the equality of lunar and terrestrial O isotope, a few years later, was originally seen as support for the impact hypothesis (although, ironically, it is now cited as a contradiction or “crisis” for the impact hypothesis). A 1984 conference on lunar origin, held in Hawaii, marked the first wide acceptance of the model, after which numerical models of giant impact processes evolved rapidly.
The initial 1974/75 work focused on the second-largest body from the terrestrial feeding zone to strike Earth during Earth’s accretion. We thus suggest that the modern isotope data as constraining the nature of the putative Earth-zone impactor, rather than by assuming a priori that the impactor must have had different isotope ratios, and suggesting a conflict with the hypothesis. Kortenkamp and Hartmann are investigating the idea of Belbruno and Gott (2005) that such an object (with terrestrial isotope ratios) may have been temporarily trapped at terrestrial Lagrangian point. (Further work has proposed to NASA Planet. Geol. & Geophys. program in 2013).
As for recent objections to the giant impact model in terms of lunar water content, it appears that production of OH and H2O on silicate dust grains (during accretion of the moon) should be considered, not to mention likely early scattering of water-rich outer-solar-system material into the terrestrial zone, possibly during lunar accretion.
REFERENCES
Belbruno, Edward and J. R. Gott III 2005. Where did the moon come from? Astron. J. 129: 1724-1745.
Hartmann, W. K. and G. P. Kuiper 1962. Concentric Structures Surrounding Lunar Basins. Comm. Lunar and Planetary Lab., 1, 51-66.
Hartmann, W. K. and D. R. Davis 1974. Satellite-sized planetesimals, I.A.U. Colloquium 28, “Planetary Satellites,” August 18-21, Cornell University, Abstract.
Hartmann, W. K. and Donald R. Davis 1975. Satellite-sized planetesimals and lunar origin. Icarus, 24, 504-515.
Show speakers
Dr William Hartmann, Planetary Science Institute, USA
Dr William Hartmann, Planetary Science Institute, USA
William K. Hartmann was first author of the 1975 Icarus paper that introduced the modern concept of lunar origin by giant impact. He is known for early work on lunar regolith, having coined the term "megaregolith" and development of a system of crater chronometry useful in dating features of the moon and Mars. He is currently involved in issues of cratering history during the first 600 Ma of solar system history. He is known also as a writer and painter.
How many impacts to form the Moon?
Dr Martin Jutzi, Physics Institute, Center for Space and Habitability, University of Bern, Switzerland
Abstract
The nearly identical isotopic composition of the Moon and the Earth’s mantle suggest a common origin. In recent numerical studies, the formation of a prelunar accretion disc of appropriate chemical composition was demonstrated in the case of a small impact in a fast rotating Earth (Cuk and Stewart, Science 338, 2012) or by involving very large impactors (Canup, Science 338, 2012). An alternative scenario was presented by Reufer et al. (Icarus 221, 2012), who considered hit-and-run collisions. We will present a follow-up study of this work, which includes also impactors with different initial compositions.
As suggested recently, a fraction of the material in the Moon forming disk could have accreted in one of the Trojan points, forming a smaller second moon (Jutzi and Asphaug, Nature 476, 2011). Such a two-Moon configuration could be stable for tens of millions of years after the giant impact (Cuk and Gladman, Icarus 199, 2009). The likely fate of the companion moon would be to collide with the Moon at low (subsonic) speed; a scenario which was suggested to have caused the lunar dichotomy (Jutzi and Asphaug, Nature 476, 2011). We will discuss various aspects and consequences of such Moon-companion moon collisions.
Show speakers
Dr Martin Jutzi, Physics Institute, Center for Space and Habitability, University of Bern, Switzerland
Dr Martin Jutzi, Physics Institute, Center for Space and Habitability, University of Bern, Switzerland
Martin Jutzi is a senior researcher at the University of Bern, Switzerland. In 2012, he was awarded the Ambizione Research Fellowship from the Swiss National Science foundation. Before that, he spent two years at the University of California in Santa Cruz as a postdoctoral researcher. He received his PhD degree in Physics in 2009 from the University of Bern and the Observatoire de la Côte d’Azur, France. He is using and developing numerical models to study impacts and (giant) collisions between small bodies, moons and planets.
Coupled Thermal-Orbital Evolution of the Early Earth-Moon System
Professor Jack Wisdom, Department of Earth, Atmospheric, and Planetary Sciences, MIT Cambridge, USA
Abstract
The isotopic similarity of the Earth and Moon has motivated a recent investigation of the formation of the Moon with a fast-spinning Earth.
Angular momentum was found to be drained from the system through the evection resonance, a resonance between the Moon and Sun. However, tidal heating within the Moon was neglected. Here we explore the coupled thermal-orbital evolution of the early Earth-Moon system, taking account of tidal heating within the Moon. We find that as the eccentricity rises once the evection resonance is reached, tidal heating within the Moon becomes especially strong. The large tidal heating in the Moon significantly lowers the tidal Q/k_2 in the Moon, with consequent early escape from the evection resonance and decay of the orbital eccentricity. Insufficient angular momentum is withdrawn from the system to be consistent with the current configuration of the Earth-Moon system.
Show speakers
Professor Jack Wisdom, Department of Earth, Atmospheric, and Planetary Sciences, MIT Cambridge, USA
Professor Jack Wisdom, Department of Earth, Atmospheric, and Planetary Sciences, MIT Cambridge, USA
-
Professor Jack Wisdom, Department of Earth, Atmospheric, and Planetary Sciences, MIT Cambridge, USA
-
Professor Jack Wisdom, Department of Earth, Atmospheric, and Planetary Sciences, MIT Cambridge, USA
- Membership status unknown
- No primary institution
Jack Wisdom is Professor of Planetary Science in the Department of Earth, Atmospheric, and Planetary Sciences at the Massachusetts Institute of Technology. He graduated in Physics from Rice University in 1976, and earned a PhD in Physics from the California Institute of Technology in 1981. He is a MacArthur Fellow and a member of the National Academy of Sciences (USA). He has coauthored two books with Gerald Jay Sussman: "Structure and Interpretation of Classical Mechanics" and "Functional Differential Geometry."
His principal research interests are in the dynamics of the solar system. He pioneered the study of chaos in the solar system. He developed a family of integration algorithms based on nonlinear dynamics that are at the core of essentially all long-term studies of planetary motion. These include the Wisdom-Holman symplectic map for the n-planet problem. With Jihad Touma, he discovered that the obliquity of Mars evolves chaotically. With Gerald Jay Sussman, he confirmed by direct numerical integration that our solar system evolves chaotically. This work shattered the long-held view of the clockwork evolution of our solar system.
Water and volatile elements in the Moon
Professor Francis Albarede, Ecole Normale Supériere de Lyon, France
Abstract
For most of the post-Apollo decades, the lunar interior has been deemed extremely dry. This lack of water can be explained both by the low volatile of the impactor and by the gravitational escape from the lunar gravity field. However, lunar apatite contains enough to support the claim that the lunar mantle holds more water than initially expected. In situ analyses of pyroclastic glass beads also show that melt inclusions in olivine crystals contain hundreds of ppm of water. Evidence of fractionated Zn isotopes, another volatile element, adds to the conundrum. We examine K, Rb, Zn and Ge concentration data on lunar basalts and extrapolate the depletion trend of the to ~300 K, the freezing point of water and show that the water content of the lunar mantle must be in the sub-ppm range. The high water contents in lunar apatites and pyroclastic glasses can be reconciled by the concentrating effects of extreme magmatic differentiation and are also consistent with a dry lunar mantle.
Show speakers
Professor Francis Albarede, Ecole Normale Supériere de Lyon, France
Professor Francis Albarede, Ecole Normale Supériere de Lyon, France
Francis Albarède is Professor of Geochemistry at the Ecole Normale Supérieure in Lyon. He is an isotope and trace element geochemist who dedicated his early career to igneous geochemistry, hydrothermal vents, palæoceanography, geochronology and Earth’s evolution. He proposed novel approaches to geochemical modeling and authored a book Introduction to Geochemistry, which was broadly used to teach geochemical modeling. He pioneered applications of MC-ICP-MS and metal isotopes to geochemistry, planetary sciences, history and now medicine. He authored more than 200 publications. Francis Albarede was Executive Editor of Earth and Planetary Science Letters from 1993 to 2000 and the Senior Editor of the Journal of Geophysical Research Solid Earth from 2000 to 2004. He is a Geochemistry and an AGU Fellow. He received the 2000 Bowen Award of the VGP Section of the American Geophysical Union and the 2008 Goldschmidt Award of the Geochemical Society.