Dust coma morphology in the Deep Impact images of Comet 9P/Tempel 1

We present an overview of the dust coma observations of Comet Tempel 1 that were obtained during the approach and encounter phases of the Deep Impact mission. We use these observations to set constraints on the pre-impact activity of the comet and discuss some preliminary results. The temporal and spatial changes that were observed during approach reveal three distinct jets rotating with a 1.7-day periodicity. The brightest jet produces an arcuate feature that expands outward with a projected velocity of about 12 m s⁻¹, suggesting that the ambient dust coma is dominated by millimeter-sized dust grains. As the spatial resolution improves, more jets and fans are revealed. We use stereo pairs of high-resolution images to put some crude constraints on the source locations of some of the brightest features. We also present a number of interesting coma features that were observed, including surface jets detected at the limb of the nucleus when the exposed ice patches are passing over the horizon, and features that appear to be jets emanating from unilluminated sources near the negative pole. We also provide a list of 10 outbursts of various sizes that were observed in the near-continuous monitoring during the approach phase.     

Testing the 14C ages and conservative behavior of dissolved 14C in a carbonate aquifer in Yucca Flat,Nevada (USA), using 36Cl from groundwater and packrat middens

Corrected groundwater ¹⁴C ages from the carbonate aquifer in Yucca Flat at the former Nevada Test Site (now the Nevada National Security Site), USA, were evaluated by comparing temporal variations of groundwater ³⁶Cl/Cl estimated with these ¹⁴C ages with published records of meteoric ³⁶Cl/Cl variations preserved in packrat middens (piles of plant fragments, fecal matter and urine). Good agreement between these records indicates that the groundwater ¹⁴C ages are reasonable and that ¹⁴C is moving with chloride without sorbing to the carbonate rock matrix or fracture coatings, despite opposing evidence from laboratory experiments. The groundwater ¹⁴C ages are consistent with other hydrologic evidence that indicates significant basin infiltration ceased 8,000 to 10,000 years ago, and that recharge to the carbonate aquifer is from paleowater draining through overlying tuff confining units along major faults. This interpretation is supported by the relative age differences as well as hydraulic head differences between the alluvial and volcanic aquifers and the carbonate aquifer. The carbonate aquifer ¹⁴C ages suggest that groundwater velocities throughout much of Yucca Flat are about 2 m/yr, consistent with the long-held conceptual model that blocking ridges of low-permeability rock hydrologically isolate the carbonate aquifer in Yucca Flat from the outlying regional carbonate flow system.     

Using groundwater noble gas measurements to confirm paleorecharge hypotheses at Pahute Mesa,Nevada National Security Site,Nevada, USA

Hydrogeology Journal - Pahute Mesa (Nevada, USA) was the site of 85 underground nuclear tests between 1965 and 1992 whose residual radiochemical inventory poses a contaminant threat to local...     

Uncertainty analysis of urban sewer system using spatial simulation of radar rainfall fields: New York City case study

The goal of this study is to investigate the uncertainty of an urban sewer system’s response under various rainfall and infrastructure scenarios by applying a recently developed nonparametric copula-based simulation approach to extreme rainfall fields. The approach allows for Monte Carlo simulation of multiple variables with differing marginal distributions and arbitrary dependence structure. The independent and identically distributed daily extreme rainfall events of the corresponding urban area, extracted from nationwide high resolution radar data stage IV, are the inputs of the spatial simulator. The simulated extreme rainfall fields were used to calculate excess runoff using the Natural Resources Conservation Service’s approach. New York City is selected as a case study and the results highlight the importance of preserving the spatial dependence of rainfall fields between the grids, even for simplified hydrologic models. This study estimates the probability of combined sewer overflows under extreme rainfall events and identifies the most effective locations in New York City to install green infrastructure for detaining excess stormwater runoff. The results of this study are beneficial for planners working on stormwater management and the approach is broadly applicable because it does not rely on extensive sewer system information.     

Using multivariate statistical analysis of groundwater major cation and trace element concentrations to evaluate groundwater flow in a regional aquifer

Groundwater samples were collected from 11 springs in Ash Meadows National Wildlife Refuge in southern Nevada and seven springs from Death Valley National Park in eastern California. Concentrations of the major cations (Ca, Mg, Na and K) and 45 trace elements were determined in these groundwater samples. The resultant data were subjected to evaluation via the multivariate statistical technique principal components analysis (PCA), to investigate the chemical relationships between the Ash Meadows and Death Valley spring waters, to evaluate whether the results of the PCA support those of previous hydrogeological and isotopic studies and to determine if PCA can be used to help delineate potential groundwater flow patterns based on the chemical compositions of groundwaters. The results of the PCA indicated that groundwaters from the regional Paleozoic carbonate aquifers (all of the Ash Meadows springs and four springs from the Furnace Creek region of Death Valley) exhibited strong statistical associations, whereas other Death Valley groundwaters were chemically different. The results of the PCA support earlier studies, where potentiometric head levels, δ¹⁸O and δD, geological relationships and rare earth element data were used to evaluate groundwater flow, which suggest groundwater flows from Ash Meadows to the Furnace Creek springs in Death Valley. The PCA suggests that Furnace Creek groundwaters are moderately concentrated Ash Meadows groundwater, reflecting longer aquifer residence times for the Furnace Creek groundwaters. Moreover, PCA indicates that groundwater may flow from springs in the region surrounding Scotty's Castle in Death Valley National Park, to a spring discharging on the valley floor. The study indicates that PCA may provide rapid and relatively cost‐effective methods to assess possible groundwater flow regimes in systems that have not been previously investigated. Copyright © 1999 John Wiley & Sons, Ltd.     

The shape, topography, and geology of Tempel 1 from Deep Impact observations

Deep Impact images of the nucleus of Comet Tempel 1 reveal pervasive layering, possible impact craters, flows with smooth upper surfaces, and erosional stripping of material. There are at least 3 layers 50-200 m thick that appear to extend deep into the nucleus, and several layers 1-20 m thick that parallel the surface and are being eroded laterally. Circular depressions show geographical variation in their forms and suggest differences in erosion rates or style over scales >1 km. The stratigraphic arrangement of these features suggests that the comet experienced substantial periods of little erosion. Smooth surfaces trending downslope suggest some form of eruption of materials from this highly porous object. The Deep Impact images show that the nucleus of Tempel 1 cannot be modeled simply as either an onion-layer or rubble pile structure.     

Major ion geochemistry of groundwaters from southern Nevada and eastern California, USA

The dissolved ionic constitutents of groundwaters are,in part,a recored of the minerals and rocks in aquifers through which the water has flowed.The chemical composition and association of these major ions in groundwaters have been used to trace groundwater flow paths and sources,In general,the chemical compostion of water in carbonate-rock aquifers in dominated by calcium,magnesium,and bicarbonate,whereas sodium,chloride,and sulfate can be dominant ions in the water that comes from volcanic aquifers or clay minerals.Since the 1990‘s,we have dealt with the geochemistry of groundwaters from more than 100 springs and wells in southern Nevada and eastrn california ,USA for major solutes and trace elements.This paper compiles the hydrochemical data of major ions of these groundwaters.Based on major ion geochemistry,groundwaters from southern Nevada and eastern California can be classified as carbonate aquifer water,volcanic aquifer water,and mixing water (either mixing of cabonate and volcanic aquifer waters or mixing with local recharges),Piper and stiff diagrams of major ions have graphically shown the general chemical characteristics,classification,and mixing relationships of groundwaters from southern Nevada and eastern California.     

Asymmetries in the distribution of H2O and CO2 in the inner coma of Comet 9P/Tempel 1 as observed by Deep Impact

Prior to the impact event, Deep Impact monitored the ambient inner coma of Comet 9P/Tempel 1 at high spatial resolution in July 2005. Gaseous H₂O and CO₂ are unambiguously detected in the infrared spectra collected with the HRI-IR spectrometer aboard Deep Impact. Detailed distribution maps of these volatiles in the inner coma, within 60 km from the nucleus, are produced from the integrated emission bands of H₂O (2.66 μm) and CO₂ (4.26 μm). Uncorrelated asymmetries are determined in the spatial distribution of both species indicating chemical heterogeneities within the nucleus. Although present at some abundance surrounding the entire nucleus, H₂O has a pronounced enhancement in abundance in the sunward direction rotational phases, evidence that the dominant process of subliming water ice from the nucleus is solar heating. In contrast, CO₂ is enhanced in the regions near the negative rotational pole of the nucleus, suggesting localized outgassing there. Both species show an increase in radiance above the limb of the nucleus toward Ecliptic North. The distribution maps also suggest that the process of dust removal from the nucleus is strongly connected to the outgassing of volatiles. Detailed study of these coma asymmetries gives insight to the relative abundances of the dominant molecular components of the inner coma, source regions of the native volatiles, anisotropic outgassing of the nucleus, and the formation and evolution of the nucleus. A quiescent water production rate for Tempel 1 on July 4, 2005, is estimated to be .