Susan Taylor

Elemental compositions of comet 81P/Wild 2 samples collected by Stardust

We measured the elemental compositions of material from 23 particles in aerogel and from residue in seven craters in aluminum foil that was collected during passage of the Stardust spacecraft through the coma of comet 81P/Wild 2. These particles are chemically heterogeneous at the largest size scale analyzed (∼180 ng). The mean elemental composition of this Wild 2 material is consistent with the CI meteorite composition, which is thought to represent the bulk composition of the solar system, for the elements Mg, Si, Mn, Fe, and Ni to 35%, and for Ca and Ti to 60%. The elements Cu, Zn, and Ga appear enriched in this Wild 2 material, which suggests that the CI meteorites may not represent the solar system composition for these moderately volatile minor elements.

Accretion rate of cosmic spherules measured at the South Pole.

Micrometeorites are terrestrially collected, extraterrestrial particles smaller than about 1u2009mm, which account for most of the mass being accreted to the Earth,. Compared with meteorites, micrometeorites more completely represent the Earth-crossing meteoroid complex, and should include fragments of asteroids, comets, Mars and our Moon, as well as pre-solar and interstellar grains,. Previous measurements of the flux of micrometeoroids that survive to the Earths surface have large uncertainties owing to the destruction of particles by weathering, inefficiencies in magnetic collection or separation techniques, low particle counts,, poor age constraint,, or highly variable concentrating processes,. Here we describe an attempt to circumvent these problems through the collection of thousands of well preserved and dated micrometeorites from the bottom of the South Pole water well, which supplies drinking water for the Scott–Amundsen station. Using this collection, we have determined precise estimates of the flux and mass distribution for 50–700-µm cosmic spherules (melted micrometeorites). Allowing for the expected abundance of unmelted micrometeorites in the samples, our results indicate that about 90% of the incoming mass of submillimetre particles evaporates during atmospheric entry. Our data indicate the loss of glass-rich and small stony spherules from deep-sea deposits,, and they provide constraints for models describing the survival probability of micrometeoroids,.

Simulated Rainfall-Driven Dissolution of TNT, Tritonal, Comp B and Octol Particles

Live-fire military training can deposit millimeter-sized particles of high explosives (HE) on surface soils when rounds do not explode as intended. Rainfall-driven dissolution of the particles then begins a process whereby aqueous HE solutions can enter the soil and groundwater as contaminants. We dripped water onto individual particles of TNT, Tritonal, Comp B and Octol to simulate how surface-deposited HE particles might dissolve under the action of rainfall and to use the data to verify a model that predicts HE dissolution as a function of particle size, particle composition and rainfall rate. Particle masses ranged from 1.1 to 17 mg and drip rates corresponded to nominal rainfall rates of 6 and 12 mmh(-1). For the TNT and Tritonal particles, TNT solubility governed dissolution time scales, whereas the lower-solubility of RDX controlled the dissolution time of both RDX and TNT in Comp B. The large, low-solubility crystals of HMX slowed but did not control the dissolution of TNT in Octol. Predictions from a drop-impingement dissolution model agree well with dissolved-mass timeseries for TNT, Tritonal and Comp B, providing some confidence that the model will also work well when applied to the rainfall-driven, outdoor dissolution of these HE particles.

Meteoritic event recorded in Antarctic ice

During systematic sampling of volcanic ash (tephra) layers at a well-known Antarctic meteorite collection site (the Allan Hills main ice field), a band of unusually dark and rounded (many spheroidal) particles was discovered. This debris layer (BIT-58) extends parallel to the stratigraphy of the ice established from the tephra bands, apparently marking a single depositional event. The shapes, internal texture, major element composition, and levels of cosmogenic nuclides of particles from within BIT-58 all strongly suggest that this material represents ablation debris from the passage of a large H-group ordinary chondrite. Preliminary cosmogenic isotope dating suggests an age of 2.8 Ma, implying that the East Antarctic ice sheet has been stable since that time. The relationship of the Bit-58 layer to known impact events is not clear.

Outdoor Weathering and Dissolution of TNT and Tritonal

Low-order detonations of military munitions scatter cm-sized chunks of high-explosives onto military range soils, where rainfall can dissolve and then transport the explosives to groundwater. We present 1 year of mass-loss data obtained from cm-sized chunks of the frequently used explosives TNT (2,4,6-trinitrotoluene) and Tritonal (an 80:20 mixture of TNT and aluminum flakes) exposed outdoors to weather and dissolve under natural conditions. The explosive chunks rested on glass frits in individual funnels and all precipitation interacting with them was collected and analyzed. Mass balance data reveal that TNT in the water samples accounts for only about one-third of the TNT lost from the chunks. The creation of photo-transformation products on the solid chunks, and their subsequent dissolution or sublimation, probably accounts for the other two-thirds. Although these products cannot, as yet, be quantified they are intrinsic to the outdoor weathering and fate of TNT-based explosives. TNT in our water samples was not photo-transformed. Thus, we used the yearlong, dissolved-mass time-series to validate a drop-impingement dissolution model for TNT. The model used measured rainfall and air temperature data as input, and the results agreed remarkably well with TNT dissolved-mass time-series measured for the year. This model can estimate annual TNT influx into range soils using annual rainfall and particle-size distributions. Nevertheless, large uncertainties remain in the numbers and sizes of TNT particles scattered on military ranges and the identities and fates of the photo-transformation products.

Seeking Unbiased Collections of Modern and Ancient Micrometeorites

Micrometeorites are sub-millimeter-sized extraterrestrial particles that survive atmospheric entry. An unbiased collection of micrometeorites should contain samples of all of the dust-producing objects in the solar system. However, because of low concentrations and rapid weathering in terrestrial environments, unbiased collections are difficult to find. Additionally, most particles have been severely heated during atmospheric entry, and the resulting changes must be understood to derive compositional information about the parent micrometeoroids. Large modern collections that can be characterized by the flux, size distribution, and micrometeorite compositional types can help constrain heating models that predict how micrometeorites are heated while entering the Earth’s atmosphere. These collections can also be used as a reference to deduce the effects of weathering on collections of ancient micrometeorites.

Field Observations of the Persistence of Comp B Explosives Residues in a Salt Marsh Impact Area

Field observations of weathering Comp B (RDX/TNT 60/40) residue were made on a live-fire training range over four years. The Comp B residue was formed by low-order detonations of 120-mm mortar projectiles. Physical changes were the disaggregation of initially solid chunks into masses of smaller diameter pieces and formation of red phototransformation products that washed off with rain or tidal flooding. Disaggregation increased the surface area of the residue, thereby increasing the potential for dissolution. The bulk of the mass of Comp B was in the craters, but solid chunks were scattered asymmetrically up to 30m away.

Dissolution of three insensitive munitions formulations.

The US military fires live munitions during training. To save soldiers lives both during training and war, the military is developing insensitive munitions (IM) that minimize unintentional detonations. Some of the compounds in the IM formulation are, however, very soluble in water, raising environmental concerns about their fate and transport. We measured the dissolution of three of these IM formulations, IMX101, IMX104 and PAX21 using laboratory drip tests and studied the accompanying changes in particle structure using micro computed tomography. Our laboratory drip tests mimic conditions on training ranges, where spatially isolated particles of explosives scattered by partial detonations are dissolved by rainfall. We found that the constituents of these IM formulations dissolve sequentially and in the order predicted by their aqueous solubility. The order of magnitude differences in solubility among their constituents produce water solutions whose compositions and concentrations vary with time. For IMX101 and IMX104, that contain 3-nitro-1,2,4-triazol-5-one (NTO), the solutions also vary in pH. The good mass balances measured for the drip tests indicate that the formulations are not being photo-or bio-transformed under laboratory conditions.

Adsorption and attenuation behavior of 3-nitro-1,2,4-triazol-5-one (NTO) in eleven soils

NTO (3-nitro-1,2,4-triazol-5-one) is one of the new explosive compounds used in insensitive munitions (IM) developed to replace traditional explosives, TNT and RDX. Data on NTO fate and transport is needed to determine its environmental behavior and potential for groundwater contamination. We conducted a series of kinetic and equilibrium batch experiments to characterize the fate of NTO in soils and the effect of soil geochemical properties on NTO-soil interactions. A set of experiments was also conducted using sterilized soils to evaluate the contribution of biodegradation to NTO attenuation. Measured pH values for NTO solutions decreased from 5.98 ± 0.13 to 3.50 ± 0.06 with increase in NTO concentration from 0.78 to 100 mg L(-1). Conversely, the pH of soil suspensions was not significantly affected by NTO in this concentration range. NTO experienced minimal adsorption, with measured adsorption coefficients being less than 1 cm(3) g(-1) for all studied soils. There was a highly significant inverse relationship between the measured NTO adsorption coefficients and soil pH (P = 0.00011), indicating the role of NTO and soil charge in adsorption processes. In kinetic experiments, 1st order transformation rate constant estimates ranged between 0.0004 h(-1) and 0.0142 h(-1) (equivalent to half-lives of 72 and 2 d, respectively), and correlated positively with organic carbon in the soil. Total attenuation of NTO was higher in untreated versus sterilized samples, suggesting that NTO was being biodegraded. The information presented herein can be used to help evaluate NTO potential for natural attenuation in soils.

Outdoor dissolution of detonation residues of three insensitive munitions (IM) formulations

We seek to understand the environmental fate of three new insensitive munitions, explosive formulations developed to reduce the incidence of unintended detonations. To this end, we measured the size distribution of residues from low order detonations of IMX 101, IMX 104, and PAX 21-filled munitions and are studying how these three formulations weather and dissolve outdoors. The largest pieces collected from the detonations were centimeter-sized and we studied 12 of these in the outdoors test. We found that the particles break easily and that the dissolution of 2,4-dinitroanisole (DNAN) is quasi-linear as a function of water volume. DNAN is the matrix and the least soluble major constituent of the three formulations. We used DNANs linear dissolution rate to estimate the life span of the pieces. Particles ranging in mass from 0.3 to 3.5 g will completely dissolve in 3-21 years given 100 cm y(-1) precipitation rates.