Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session K62: Materials at TPa: a New Frontier of Materials PhysicsInvited
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Sponsoring Units: DCOMP GSCCM Chair: Dario Alfe, University College London Room: BCEC 258C |
Wednesday, March 6, 2019 8:00AM - 8:36AM |
K62.00001: Exoplanets: from Discovery to Characterization and Beyond Invited Speaker: Sara Seager Thousands of exoplanets are known to orbit nearby stars with evidence that nearly all stars in our Milky Way Galaxy have planets. Beyond their discovery, a new era of “exoplanet characterization” is underway with an astonishing diversity of exoplanets driving the fields of planet formation and evolution, interior structure, atmospheric science, and orbital dynamics to new depths. Exoplanets with masses and average densities that have no solar system counterparts are mysteries in their formation pathways as well as their interior composition and structure. The push to find smaller and smaller planets down to Earth size is succeeding and motivating the next generation of planetary models and telescopes to have the capability to find and identify planets that may be like Earth. |
Wednesday, March 6, 2019 8:36AM - 9:12AM |
K62.00002: Phase transitions in mantle silicates and the internal structure of terrestrial exoplanets Invited Speaker: Koichiro Umemoto The highest-pressure form in the Earth of the major mantle silicate MgSiO3-bridgmanite is post-perovskite (PPv). Knowledge of the fate of PPv at higher pressures relevant for super-Earth-type planets is fundamental for us to start modeling the internal structure and dynamics of these planets. In this talk I will review the sequence of phase transitions we discovered in pure MgSiO3 up to 4 TPa, as well as in aggregates of MgSiO3+MgO and MgSiO3+SiO2 with variable Mg/Si abundances. New phases in the (MgO)n(SiO2)m system have been discovered [1-5]. Such phases involve dissociation and recombination reactions in the MgSiO3+MgO+SiO2 system, some of them very surprising, but all ending-up in the dissociated elementary oxides, MgO+SiO2, above 3.1 TPa [1]. These transitions produce density discontinuities in planetary interiors and the consequences of these transitions for the internal structure of terrestrial planets [6] with up to 20 Earth masses will be discussed. |
Wednesday, March 6, 2019 9:12AM - 9:48AM |
K62.00003: Mass-dependent Dynamics of Terrestrial Exoplanets Using ab initio Mineral Properties Invited Speaker: Arie Van den Berg We present new modelling results for the internal structure and convective dynamics of large terrestrial (rocky) exoplanets. For upto 20 Earth masses (Me) our results show pressure and temperature (P,T) of several Terapascal (TPa) and 10000 Kelvin in the silicate mantle. |
Wednesday, March 6, 2019 9:48AM - 10:24AM |
K62.00004: Phase Transitions Beyond Post-Perovskite in Neighborite (NaMgF3) to 1.6 Mbars Invited Speaker: Thomas Duffy Neighborite, NaMgF3, is used as a model system for understanding ultra-high pressure phase transitions in ABX3 systems such as MgSiO3. In this work, we have studied the high-pressure behavior of NaMgF3 to 1.6 Mbars using the laser-heated diamond anvil cell technique coupled with synchrotron x-ray diffraction. Our work reveals a complex sequence of high-pressure phases beyond post-perovskite in this ABX3 system. The phase transition sequence in NaMgF3 is: NaMgF3 (perovskite) → NaMgF3 (post perovskite) → NaMgF3 (Sb2S3-type) → NaF (B2-type) + NaMg2F5 (P21/c) → NaF (B2) + MgF2 (cotunnite-type). Our results demonstrate the existence of a post-post-perovskite phase, followed a two-stage dissociation into binary fluorides. This work is the first experimental report of a dissociation of a post-perovskite in any known ABX3 system. A similar sequence of transition is predicted to occur in MgSiO3 at ultrahigh pressures where it has implications for the mineralogy and dynamics large, rocky extra-solar planets. |
Wednesday, March 6, 2019 10:24AM - 11:00AM |
K62.00005: Laser Focus on Planets Invited Speaker: Gilbert Collins A new laboratory exploration of the deep interior states and processes for solar and extrasolar planets is underway. KiloJoule to MegaJoule laser compression data and first principles calculations combined with recent observational planet discoveries provide fresh perspectives for the qualities and implications of these massive objects throughout the universe. Recent experimental results for silicates and water reveal dramatic chemical changes emerge at millions of atmosphere pressure and several thousand Kelvin, giving rise to polymeric silicates and superionic water. New equation of state data for iron to tens of millions of atmospheres provides insight into the deep interior core conditions for extrasolar terrestrial planets. At still higher pressures, approaching atomic pressures (294 Mbar = 29.4 TPa) atoms can be brought together closer than a deBroglie wavelength and even in some cases the Bohr radius where core as well as valence electrons (keV as well as eV energy levels) engage in bonding and where a new quantum behavior emerges. |
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