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Hope A. Ishii Faculty

Hope A. Ishii
Associate Researcher
Director of Advanced Electron Microscopy Center


Ph.D., Stanford University, 2002

Email: hope.ishii@higp.hawaii.edu
Office: POST 509B
Phone Number: (808) 956-7755
Fax Number: (808) 956-6322

University of Hawai'i at Manoa
Hawai'i Institute of Geophysics and Planetology
1680 East-West Road, POST 602
Honolulu, HI 96822
USA


Research Interests:
Director of Advanced Electron Microscopy Center; Cosmochemistry, extraterrestrial materials, focused ion beam and transmission electron microscope analysis

Projects:
Microscopy on Primitive Small Solar System Bodies
We now have new capabilities at UH for characterization of meteoritic materials – as well as other natural and technological materials! An FEI Titan G3 60-300 kV dual-spherical-aberration-corrected (Scanning) Transmission Electron Microscope (courtesy of NASA) and an FEI Helios 660 dual beam Focused Ion Beam instrument are housed in the POST basement. My research typically revolves around the sample preparation and analysis capabilities of these two extremely powerful beasties. Together, they allow us to extract few-micron-sized samples from specific locations, thin them to electron-transparency and then study texture, petrography, elemental chemistry, structure and bonding at the micro- to nano-scale.

Mauna Loa Cosmic Dust Collection
Comets formed as small icy bodies far from the young Sun and have been preserved by their distant orbits like icy time capsules. If comets get bumped into an orbit near the Sun, then their ices sublime and release dust. Comets – and asteroids – also release dust in collisions. Every year, 30,000-40,000 tons of extraterrestrial dust reaches Earth-crossing orbits and trickles through our atmosphere to settle on the Earth’s surface. Since this dust includes organic matter, it is very likely that comets and asteroids helped to seed the Earth with the pre-biotic materials for the development of life. In this project, we are taking advantage of unique meteorological conditions atop Mauna Loa on Hawai‘i’s Big Island to collect pristine, primitive dust from comets and asteroids directly from the air. This approach removes contamination problems caused by historical collection methods. At nighttime, the prevailing winds blow downslope, bringing clean Central Pacific air from the free lower troposphere to MLO. (Since 1958, atmospheric scientists have used this effect to measure the famous Keeling Curve of CO2 levels in the atmosphere.) These downslope flows have low terrestrial and manmade particulate levels giving a higher percentage of extraterrestrial particles. This project is just getting underway, and we hope to be able to collect large enough cometary particles to analyze their organics with collaborators at NASA Goddard Space Flight Center.

Comet and Asteroid Dust
This project involves analysis of NASA Stardust mission samples returned from comet 81P/Wild 2, bona fide comet dust from a Kuiper Belt object! The research focus has been on the relationship between comet Wild 2 and other small Solar System bodies, time scales of formation of Wild 2 dust components, as well as the complexities of the hypervelocity capture process on interpreting the original state of the dust. A future project is planned working on understanding space weathering effects from samples returned by the JAXA Hayabusa mission to the asteroid 25143 Itokawa, an Apollo-group S-type asteroid.

Amorphous Silicates in Primitive Solar System Objects
Amorphous silicates are arguably the least-understood solids in extraterrestrial materials, despite the fact that they make up the majority of rock-forming material in the interstellar medium (ISM) from which our Solar System grew. Over 99% of ISM silicates are amorphous, but of those amorphous silicates that contributed to the birth of our Sun, we do not yet know what fraction survived in recognizable form. Due to instrumental detection limits, it is likely that a far larger proportion of amorphous silicates observed in cometary samples are remnants of the presolar cloud of dust and gas than can be identified by isotope anomalies, one indicator of presolar origin. Those that did survive are to be found in very primitive Solar System objects, comets and maybe some asteroids, that have experienced the least alteration since they formed. This project has the exciting potential to improve our understanding of which amorphous silicates in samples in our lab are part of the first building blocks of our Solar System by improving our understanding of the inter-relationships – or lack thereof – between cometary and asteroidal amorphous silicates and with ISM amorphous silicates observed and modeled by astronomers. Samples include chondritic porous interplanetary dust particles and ultracarbonaceous Antarctic micrometeorites believed to originate from comets, comet 81P/Wild 2 samples returned by Stardust, and fine-grained matrices of highly pristine chondrites.

Nebular versus Parent Body Alteration
Critical to interpreting data from meteorite samples is understanding whether the alteration processes they experienced occurred prior to or after accretion on parent bodies, and the key evidence is often on the sub-micron scale. This project focuses on understanding the mechanisms and conditions of alteration in primitive meteorite samples, often with complementary isotopic measurements made with collaborators here at UH, Washington University at St. Louis and at CalTech. This project relies on both FIB and TEM in order to study samples from chondritic chondrite meteorites with well-preserved petrographic relationships.

Relevant Links:

Publications Link:  http://www.higp.hawaii.edu/publications/faculty/Ishii_publications_list_01-2018.pdf


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