Meteoritics & Planetary Science, Volume 41, Number 2 (2006)
http://hdl.handle.net/10150/641264
2024-03-29T04:33:32ZTOF-SIMS analysis of Allende projectiles shot into silica aerogel
http://hdl.handle.net/10150/656698
TOF-SIMS analysis of Allende projectiles shot into silica aerogel
Stephan, Thomas; Butterworth, Anna L.; Hörz, Friedrich; Snead, Christopher J.; Westphal, Andrew J.
Powdered Allende projectiles were fired into silica aerogel at 6.1 km/sec in order to evaluate particle retrieval and analysis techniques for samples from the Stardust mission. Since particles may disintegrate and ablate along the penetration paths in a high-porosity aerogel, TOF-SIMS analysis may be a suitable method to determine the distribution of such materials along the tracks as well as potential compositional modifications. Therefore, two 350 micrometer-sized tracks, residing at the surface of a keystone specimen that was flattened between two silicon chips, were analyzed. TOF-SIMS allows for a detailed study of the chemical composition of particles that survived the impact mostly intact and of fine-grained material from disintegrated projectiles. In the investigated keystone, material from light gas gun debris dominated. Besides the two tracks, a continuous, 40-micrometer-thick surface layer of implanted material - probably gun residue - was found. One of the two analyzed tracks is compositionally distinct from this surface layer and is likely to contain residual material of an Allende projectile. The analyses clearly demonstrate that tracks, resulting from impactors in the 5-10 micrometer size range, can be successfully analyzed with TOF-SIMS.
2006-01-01T00:00:00ZMacroscopic subdivision of silica aerogel collectors for sample return missions
http://hdl.handle.net/10150/656699
Macroscopic subdivision of silica aerogel collectors for sample return missions
Ishii, H. A.; Bradley, J. P.
Silica aerogel collector tiles have been employed for the collection of particles in low Earth orbit and, more recently, for the capture of cometary particles by NASA's Stardust mission. Reliable, reproducible methods for cutting these and future collector tiles from sample return missions are necessary to maximize the science output from the extremely valuable embedded particles. We present a means of macroscopic subdivision of collector tiles by generating large-scale cuts over several centimeters in silica aerogel with almost no material loss. The cut surfaces are smooth and optically clear allowing visual location of particles for analysis and extraction. This capability is complementary to the smaller-scale cutting capabilities previously described (Westphal 2004; Ishii 2005a, 2005b) for removing individual impacts and particulate debris in tiny aerogel extractions. Macroscopic cuts enable division and storage or distribution of portions of aerogel tiles for immediate analysis of samples by certain techniques in situ or further extraction of samples suited for other methods of analysis. The capability has been implemented in the Stardust Laboratory at NASA's Johnson Space Center as one of a suite of aerogel cutting methods to be used in Stardust sample curation.
2006-01-01T00:00:00ZBook Review: Theaters of Time and Space: American Planetaria, 1930-1970, Jordan D. Marché
http://hdl.handle.net/10150/656107
Book Review: Theaters of Time and Space: American Planetaria, 1930-1970, Jordan D. Marché
Ratcliffe, Martin
Book Review: Theaters of Time and Space: American Planetaria, 1930-1970, Jordan D. Marché. Rutgers University Press (2005).
2006-01-01T00:00:00ZAustralasian microtektites and associated impact ejecta in the South China Sea and the Middle Pleistocene supereruption of Toba
http://hdl.handle.net/10150/656106
Australasian microtektites and associated impact ejecta in the South China Sea and the Middle Pleistocene supereruption of Toba
Glass, Billy P.; Koeberl, Christian
Australasian microtektites were discovered in Ocean Drilling Program (ODP) Hole 1143A in the central part of the South China Sea. Unmelted ejecta were found associated with the microtektites at this site and with Australasian microtektites in Core SO95-17957-2 and ODP Hole 1144A from the central and northern part of the South China Sea, respectively. A few opaque, irregular, rounded, partly melted particles containing highly fractured mineral inclusions (generally quartz and some K feldspar) and some partially melted mineral grains, in a glassy matrix were also found in the microtektite layer. The unmelted ejecta at all three sites include abundant white, opaque grains consisting of mixtures of quartz, coesite, and stishovite, and abundant rock fragments which also contain coesite and, rarely, stishovite. This is the first time that shock-metamorphosed rock fragments have been found in the Australasian microtektite layer. The rock fragments have major and trace element contents similar to the Australasian microtektites and tektites, except for higher volatile element contents. Assuming that the Australasian tektites and microtektites were formed from the same target material as the rock fragments, the parent material for the Australasian tektites and microtektites appears to have been a fine-grained sedimentary deposit. Hole 1144A has the highest abundance of microtektites (number/cm^2) of any known Australasian microtektite-bearing site and may be closer to the source crater than any previously identified Australasian microtektite-bearing site. A source crater in the vicinity of 22 degrees N and 10 degrees E seems to explain geographic variations in abundance of both the microtektites and the unmelted ejecta the best; however, a region extending NW into southern China and SE into the Gulf of Tonkin explains the geographic variation in abundance of microtektites and unmelted ejecta almost as well. The size of the source crater is estimated to be 43 +/- 9 km based on estimated thickness of the ejecta layer at each site and distance from the proposed source. A volcanic ash layer occurs just above the Australasian microtektite layer, which some authors suggest is from a supereruption of the Toba caldera complex. We estimate that deposition of the ash occurred ~800 ka ago and that it is spread over an area of at least 3.7 x 10^7 km^2.
2006-01-01T00:00:00Z