David Kirkpatrick

October 2, 2010

The Geological Society of America goes 3D

I think the title says it all …

The release:

GSA Press Release – October 2010 Geosphere Highlights

Boulder, CO, USA – This month’s themed issue, “Advances in 3D imaging and analysis of geomaterials,” edited by Guilherme A.R. Gualda, Don R. Baker, and Margherita Polacci, features papers from the 2009 AGU Joint Assembly session “Advances in 3-D Imaging and Analysis of Rocks and Other Earth Materials.” Studies include 3-D imaging and analysis techniques for Wild 2 comet material returned from the NASA Stardust mission and the first 3-D X-ray scans of crystals from the Dry Valleys, Antarctica.

Keywords: Voxels, microtomography, fractures, NASA Stardust Mission, Wild 2, aerogel, Dry Valleys, Antarctica, geophysics, microearthquakes, Mexico, zircon dating, database, InSAR.

Highlights are provided below. Review abstracts for this issue at http://geosphere.gsapubs.org/.

Non-media requests for articles may be directed to GSA Sales and Service, gsaservice@geosociety.org .

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Introduction: Advances in 3D imaging and analysis of geomaterials
Guilherme A.R. Gualda, Vanderbilt University, Earth & Environmental Sciences, Station B #35-1805, Nashville, Tennessee 37235, USA

Excerpt: Beginning in the 1970s, the availability of computers led to the development of procedures for computer-assisted acquisition and reconstruction of 3-D tomographic data, in particular using X-rays. X-ray tomography is now a mature technique that is used routinely. It has been applied to a wide array of geomaterials, from rocks to fossils to diverse experimental charges, to name a few. The ability to create 3-D maps with millions to billions of volume elements (voxels) created the challenge of processing and analyzing such large amounts of data. While qualitative observations in 3-D yield significant insights into the nature of geomaterials and geological processes, it is in the pursuit of quantitative data that 3-D imaging shows its greatest potential. The continued improvements in computer capabilities have led to ever more sophisticated procedures for 3D image analysis. The papers in this issue encompass a wide range of topics, from applications of established techniques to a variety of materials, the development of new imaging techniques, and the description of improved imaging and analysis techniques.

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3D imaging of volcano gravitational deformation by computerized X-ray micro-tomography
M. Kervyn et al., Dept. of Geology and Soil Science, Ghent University, Krijgslaan 281/S8, 9000 Gent, Belgium

Volcanoes are known to be unstable constructs that can deform gravitationally when they build upon weak sedimentary layers. The structures and velocity of deformation depend on the volcano loading and the properties of the underlying layers. These processes can be studied with scaled laboratory experiments in which volcanoes are simulated by a mixture of sand and plaster. Silicone is used to simulate the weak underlying layers. This team from Belgium and France, lead by M. Kervyn of Ghen University, presents the results of imaging such experiments with X-rays. The micro-tomography technology used in imaging these experiments enables the virtual re-construction of the 3-D shape of the deformed experiment. Virtual cross-sections through the experiment provide a new way to characterize the faults and fissures forming within the experimental volcano during its deformation. Results from a range of experiments with different geometrical characteristics provide a better understanding of the impact of such gravitational deformation, currently recorded at several well-known volcanoes on Earth (e.g. Etna, Kilauea), on the construct’s structure at depth and its potential zones of weakness.

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Three-dimensional measurement of fractures in heterogeneous materials using high-resolution X-ray computed tomography
Richard A. Ketcham et al., Dept. of Geological Sciences, Jackson School of Geosciences, 1 University Station C1100, The University of Texas at Austin, Austin, Texas 78712-0254, USA

When present, fractures tend to dominate fluid flow though rock bodies, and characterizing fracture networks is necessary for understanding these flow regimes. Specialized CAT scanning has long been an important tool in imaging fractures in 3-D in rock samples. However, a number of factors have reduced the fidelity of such data, including the natural heterogeneity of real rocks and the limited resolution of CAT scanning. Richard A. Ketcham of The University of Texas at Austin and colleagues present new, general methods for overcoming these problems and extracting the best-quality information possible concerning fracture aperture, roughness, and orientation, even in highly heterogeneous rocks. The methods are also general enough that they can be applied to similar situations, such as measuring mineral veins. This work was funded in part by U.S. National Science Foundation grants EAR-0113480 and EAR-0439806.

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Laser scanning confocal microscopy of comet material in aerogel
Michael Greenberg and Denton S. Ebel, Dept. of Earth and Planetary Sciences, American Museum of Natural History, Central Park West at 79th Street, New York, New York 10024, USA

The NASA Stardust mission returned extraterrestrial material from the comet Wild 2 — the first solid sample-return mission since the Apollo era. Particles from the tail of Wild 2 were captured in aerogel, low-density, translucent, silica foam at a relative velocity of 6.1 km per second. Upon impact into the aerogel, particles from the tail of the comet were fragmented, melted, and ablated, creating cavities, or tracks — each of which is unique to the original particle before capture. Michael Greenberg and Denton S. Ebel of the American Museum of Natural History present nondestructive 3-D imaging and analysis techniques for comet material returned from the NASA Stardust mission. The methods described in this paper represent the highest resolution 3-D images of Stardust material to date. The procedures described here will easily extend to other translucent samples in the geosciences.

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September 28, 2008

The trouble with moon dust

The release from the Geological Society of America:

NASA’S Dirty Secret: Moon Dust

Boulder, CO, USA–The Apollo Moon missions of 1969-1972 all share a dirty secret. “The major issue the Apollo astronauts pointed out was dust, dust, dust,” says Professor Larry Taylor, Director of the Planetary Geosciences Institute at the University of Tennessee. Fine as flour and rough as sandpaper, Moon dust caused ‘lunar hay fever,’ problems with space suits, and dust storms in the crew cabin upon returning to space.

Taylor and other scientists will present their research on lunar dust at the “Living on a Dusty Moon” session on Thursday, 9 October 2008, at the Joint Meeting of the Geological Society of America (GSA), Soil Science Society of America (SSSA), American Society of Agronomy (ASA), Crop Science Society of America (CSSA), and Gulf Coast Association of Geological Societies (GCAGS) in Houston, Texas, USA. NASA will use these findings to plan a safer manned mission to the Moon in 2018. Taylor will also deliver a Pardee Keynote Session talk on Sunday, 5 October 2008 entitled “Formation and Evolution of Lunar Soil from An Apollo Perspective.”

The trouble with moon dust stems from the strange properties of lunar soil. The powdery grey dirt is formed by micrometeorite impacts which pulverize local rocks into fine particles. The energy from these collisions melts the dirt into vapor that cools and condenses on soil particles, coating them in a glassy shell.

These particles can wreak havoc on space suits and other equipment. During the Apollo 17 mission, for example, crewmembers Harrison “Jack” Schmitt and Gene Cernan had trouble moving their arms during moonwalks because dust had gummed up the joints. “The dust was so abrasive that it actually wore through three layers of Kevlar-like material on Jack’s boot,” Taylor says.

To make matters worse, lunar dust suffers from a terrible case of static cling. UV rays drive electrons out of lunar dust by day, while the solar wind bombards it with electrons by night. Cleaning the resulting charged particles with wet-wipes only makes them cling harder to camera lenses and helmet visors. Mian Abbas of the National Space Science and Technology Center in Huntsville, Alabama, will discuss electrostatic charging on the moon and how dust circulates in lunar skies.

Luckily, lunar dust is also susceptible to magnets. Tiny specks of metallic iron (Fe0) are embedded in each dust particle’s glassy shell. Taylor has designed a magnetic filter to pull dust from the air, as well as a “dust sucker” that uses magnets in place of a vacuum. He has also discovered that microwaves melt lunar soil in less time than it takes to boil a cup of tea. He envisions a vehicle that could microwave lunar surfaces into roads and landing pads as it drives, and a device to melt soil over lunar modules to provide insulation against space radiation. The heating process can also produce oxygen for breathing.

But the same specks of iron that could make moon dust manageable also pose a potential threat to human health, according to Bonnie Cooper at NASA’s Johnson Space Center. “Those tiny blebs of pure iron we see on the surface of lunar grains are likely to be released from the outside edges of the particle in the lungs and enter the bloodstream,” she says. Preliminary studies suggest that the inhalation of lunar dust may pose a health hazard, possibly including iron toxicity. Members of NASA’s Lunar Airborne Dust Toxicity Advisory Group, Cooper, Taylor, and colleagues are studying how moon dust affects the respiratory system. They plan to set a lunar dust exposure standard by 2010, in time for NASA engineers to design a safer and cleaner trip to the Moon.

**WHEN & WHERE**

Thursday, 9 October, 8:00 AM – noon
George R. Brown Convention Center, Room 310AD

View abstracts, session 345: “Living on a Dusty Moon”
Paper 345-1 (Taylor): “Formation of Lunar Dust: Unique Properties for a Human Outpost” (8:00 AM)
Paper 345-9 (Cooper): “Physical and Biological Hazards of Lunar Dust and Their Impact on Habitat and Space Suit Design” (10:00 AM)

**IMAGES AVAILABLE**

Click on photos for larger images.

NASA

The surface of the Moon is covered in powdery gray dust that caused unforeseen problems for NASA astronauts. Apollo 17 astronaut Harrison “Jack” Schmitt took this picture of Eugene Cernan during their third and last walk on the lunar surface in December of 1972. Image credit: NASA

 

Larry Taylor

Lunar dust as seen under a microscope. Each is covered in a glassy coating that may be smooth and round or jagged and sharp. Particle types shown include plagioclase (lower left, white), volcanic glass beads (upper right, smooth and black), impact-glass beads (upper left, black but rough), rock chips (rough and gray) and agglutinate (center, rough and gray, with hole). For scale, the smallest round bead at upper right is approximately 1 mm in diameter. Image credit: Larry Taylor

 

Larry Taylor

Flecks of metallic iron (white) embedded in the glassy coating of lunar dust. All lunar impact glass contains grains of iron a tenth of a micron across or less. Image credit: Larry Taylor

 

Larry Taylor

Lunar dust melts readily when exposed to microwave energy. Professor Larry Taylor of the University of Tennessee envisions a lunar paver fitted with microwave generators that could sinter, or melt, lunar soils into landing strips or roads. Image credit: Larry Taylor