Hope Ami Ishii
University of Hawaii
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Featured researches published by Hope Ami Ishii.
Philosophical Transactions of the Royal Society A | 2017
Diane H. Wooden; Hope Ami Ishii; Michael E. Zolensky
Comet dust is primitive and shows significant diversity. Our knowledge of the properties of primitive cometary particles has expanded significantly through microscale investigations of cosmic dust samples (anhydrous interplanetary dust particles (IDPs), chondritic porous (CP) IDPs and UltraCarbonaceous Antarctic micrometeorites, Stardust and Rosetta), as well as through remote sensing (Spitzer IR spectroscopy). Comet dust are aggregate particles of materials unequilibrated at submicrometre scales. We discuss the properties and processes experienced by primitive matter in comets. Primitive particles exhibit a diverse range of: structure and typology; distribution of constituents; concentration and form of carbonaceous and refractory organic matter; Mg- and Fe-contents of the silicate minerals; sulfides; existence/abundance of type II chondrule fragments; high-temperature calcium–aluminium inclusions and ameboid-olivine aggregates; and rarely occurring Mg-carbonates and magnetite, whose explanation requires aqueous alteration on parent bodies. The properties of refractory materials imply there were disc processes that resulted in different comets having particular selections of primitive materials. The diversity of primitive particles has implications for the diversity of materials in the protoplanetary disc present at the time and in the region where the comets formed. This article is part of the themed issue ‘Cometary science after Rosetta’.
Icarus | 2017
Heather M. Kaluna; Hope Ami Ishii; J. P. Bradley; Jeffrey J. Gillis-Davis; Paul G. Lucey
Abstract Simulated space weathering experiments on volatile-rich carbonaceous chondrites (CCs) have resulted in contrasting spectral behaviors (e.g. reddening vs bluing). The aim of this work is to investigate the origin of these contrasting trends by simulating space weathering on a subset of minerals found in these meteorites. We use pulsed laser irradiation to simulate micrometeorite impacts on aqueously altered minerals and observe their spectral and physical evolution as a function of irradiation time. Irradiation of the mineral lizardite, a Mg-phyllosilicate, produces a small degree of reddening and darkening, but a pronounced reduction in band depths with increasing irradiation. In comparison, irradiation of an Fe-rich aqueously altered mineral assemblage composed of cronstedtite, pyrite and siderite, produces significant darkening and band depth suppression. The spectral slopes of the Fe-rich assemblage initially redden then become bluer with increasing irradiation time. Post-irradiation analyses of the Fe-rich assemblage using scanning and transmission electron microscopy reveal the presence of micron sized carbon-rich particles that contain notable fractions of nitrogen and oxygen. Radiative transfer modeling of the Fe-rich assemblage suggests that nanometer sized metallic iron (npFe0) particles result in the initial spectral reddening of the samples, but the increasing production of micron sized carbon particles (µpC) results in the subsequent spectral bluing. The presence of npFe0 and the possible catalytic nature of cronstedtite, an Fe-rich phyllosilicate, likely promotes the synthesis of these carbon-rich, organic-like compounds. These experiments indicate that space weathering processes may enable organic synthesis reactions on the surfaces of volatile-rich asteroids. Furthermore, Mg-rich and Fe-rich aqueously altered minerals are dominant at different phases of the aqueous alteration process. Thus, the contrasting spectral slope evolution between the Fe- and Mg-rich samples in these experiments may indicate that space weathering trends of volatile-rich asteroids have a compositional dependency that could be used to determine the aqueous histories of asteroid parent bodies.
Proceedings of the International Astronomical Union | 2015
C. Engrand; J. Duprat; Noémie Bardin; E. Dartois; Hugues Leroux; Eric Quirico; Karim Benzerara; Laurent Remusat; Elena Dobrica; Lucie Delauche; John P. Bradley; Hope Ami Ishii; Martin Hilchenbach
Comets are probably the best archives of the nascent solar system, 4.5 Gyr ago, and their compositions reveal crucial clues on the structure and dynamics of the early protoplanetary disk. Anhydrous minerals (olivine and pyroxene) have been identified in cometary dust for a few decades. Surprisingly, samples from comet Wild2 returned by the Stardust mission in 2006 also contain high temperature mineral assemblages like chondrules and refractory inclusions, which are typical components of primitive meteorites (carbonaceous chondrites - CCs). A few Stardust samples have also preserved some organic matter of comet Wild 2 that share some similarities with CCs. Interplanetary dust falling on Earth originate from comets and asteroids in proportions to be further constrained. These cosmic dust particles mostly show similarities with CCs, which in turn only represent a few percent of meteorites recovered on Earth. At least two (rare) families of cosmic dust particles have shown strong evidences for a cometary origin: the chondritic porous interplanetary dust particles (CP-IDPs) collected in the terrestrial stratosphere by NASA, and the ultracarbonaceous Antarctic Micrometeorites (UCAMMs) collected from polar snow and ice by French and Japanese teams. Analyses of dust particles from the Jupiter family comet 67P/Churyumov-Gerasimenko by the dust analyzers on Rosetta orbiter (COSIMA, GIADA, MIDAS) suggest a relationship to interplanetary dust/micrometeorites. A growing number of evidences highlights the existence of a continuum between asteroids and comets, already in the early history of the solar system.
Icarus | 2017
Jeffrey J. Gillis-Davis; Paul G. Lucey; John P. Bradley; Hope Ami Ishii; Heather M. Kaluna; Anumpam Misra; Harold C. Connolly
Archive | 2010
Hope Ami Ishii; Frank J. Stadermann; Christine Floss; D. J. Joswiak; James P. Bradley; Nick E. Teslich; Donald E. Brownlee; Graciela Matrajt; Glenn J. MacPherson; Kevin D. McKeegan
Archive | 2010
Penelope J. Wozniakiewicz; Hope Ami Ishii; Anton T. Kearsley; Mark J. Burchell; James P. Bradley; Nick E. Teslich; M. J. Cole
Archive | 2010
Hope Ami Ishii; James P. Bradley; L. Bonal; Alexander N. Krot; Kazuyuki Nagashima; Gary R. Huss
Archive | 2011
James P. Bradley; Penelope J. Wozniakiewicz; Hope Ami Ishii
Journal Name: The Astrophysical Journal Letters, vol. 731, n/a, March 25, 2011, pp. 6; Journal Volume: 731 | 2010
Benjamin Jacobsen; Jennifer E. P. Matzel; Ian D. Hutcheon; Alexander N. Krot; Qing-Zhu Yin; Kazuhide Nagashima; Erick C. Ramon; Peter K. Weber; Hope Ami Ishii; Fred J. Ciesla
Archive | 2009
Bo Holm Jacobsen; Jennifer E. P. Matzel; Ian D. Hutcheon; Erick C. Ramon; Alexander N. Krot; Hope Ami Ishii; Kazuyuki Nagashima; Q.-Z. Yin