Excitation of the W triplet Delta (U), W singlet Delta (U), B prime triplet Sigma (U) (minus), and A prime singlet Epsison (U) (minus) states of N2 by electron impact

Electron energy-loss spectra have been obtained for N2 at 20.6 eV impact energy, and scattering angles of 10-138 deg. The differential cross section for excitation of the W triplet Delta(U) state is the largest triplet-state cross section at all scattering angles, and is the largest inelastic cross section at angles greater than 70 degrees. (Author Modified Abstract

The excitation of O2 in auroras

Newly measured electron impact cross sections for excitation of the a 1 Delta g and b 1 Sigma g+ electronic states of O2 were employed to predict the absolute volume emission rates from these states under auroral conditions. A secondary electron electron flux typical of an IBC II nighttime aurora was used and the most important quenching processes were included in the calculations. The new excitation cross sections for the a 1 Delta g and b 1 Sigma g+ states are more than an order of magnitude larger than previous estimates, and lead to correspondingly greater intensities in the atmospheric and IR-atmospheric band systems. The calculated intensity ratios of the volume emission rates of 7621 A and 1.27 microns to that for 3914 A are smaller than obtained from aircraft observations and recent rocket experiments

Molecular Hydrogen Optical Depth Templates for FUSE Data Analysis

The calculation and use of molecular hydrogen optical depth templates to quickly identify and model molecular hydrogen absorption features longward of the Lyman edge at 912 Angstroms are described. Such features are commonly encountered in spectra obtained by the Far Ultraviolet Spectroscopic Explorer and also in spectra obtained by the Space Telescope Imaging Spectrograph, albeit less commonly. Individual templates are calculated containing all the Lyman and Werner transitions originating from a single rotational state (J'') of the 0th vibrational level (v'') of the ground electronic state. Templates are provided with 0.01 Angstrom sampling for doppler parameters ranging from 2 <= b <= 20 km s^-1 and rotational states 0 <= J'' <= 15. Optical depth templates for excited vibrational states are also available for select doppler parameters. Each template is calculated for a fiducial column density of log[N(cm^-2)] = 21 and may be scaled to any column less than this value without loss of accuracy. These templates will facilitate the determination of the distribution of molecular hydrogen column density as a function of rotational level. The use of these templates will free the user from the computationally intensive task of calculating profiles for a large number of lines and allow concentration on line profile or curve-of-growth fitting to determine column densities and doppler parameters. The templates may be downloaded freely from http://www.pha.jhu.edu/~stephan/h2ools2.htmlComment: 20 pages, 2 tables, 6 figures, submitted to PASP 02-04-2003 Accepted for publication on 03-05-2003 with revisions, including modified fg1, modifed fg6 to become fg2 to support improved error discussion. To appear in the June 2003 issue of the PAS

Arrested versus active silica diagenesis reaction boundaries—A review of seismic diagnostic criteria

This paper evaluates previously proposed diagnostic criteria that can be used to determine whether or not there is active migration of the opal-A to opal-CT transition zone (TZA/CT). The criteria are based on the interpretation of 2D and 3D seismic surveys and are therefore geometrical. They involve an assessment of the relationship of the TZA/CT with polygonal fault systems, differential compaction structures and tectonic folds. The most robust evidence for an inactive ‘reaction front’ between opal-A and opal-CT bearing sediments is the discordance of the TZA/CT relative to present-day isotherms. Any of these may be persuasive as diagnostic criteria for the upward arrest of the diagenetic transformation at a regional scale, but actual truncation of the TZA/CT at the modern seabed is definitive for arrested diagenesis. This study argues that diagenetic assessment based solely on a single criterion independently is not reliable as an indicator for the current state of a silica transition. As a conclusion, the analysed seismic/structural criteria should be synthesised to provide a more credible interpretation for silica diagenesis. The use of modern 2D and 3D seismic data for the reconstruction of the diagenetic history of opaline silica bearing sediments offers a new approach to the study of silica diagenesis at a regional scale

The Regolith of 4 Vesta - Inferences from Howardites

Asteroid 4 Vesta is quite likely the parent asteroid of the howardite, eucrite and diogenite meteorites - the HED clan. Eucrites and diogenites are the products of igneous processes; the former are basaltic composition rocks from flows, and shallow and deep intrusive bodies, whilst the latter are cumulate orthopyroxenites thought to have formed deep in the crust. Impact processes have excavated these materials and mixed them into a suite of polymict breccias. Howardites are polymict breccias composed mostly of clasts and mineral fragments of eucritic and diogenitic parentage, with neither end-member comprising more than 90% of the rock. Early work interpreted howardites as representing the lithified regolith of their parent asteroid. Recently, howardites have been divided into two subtypes; fragmental howardites, being a type of non-regolithic polymict breccia, and regolithic howardites, being lithified remnants of the active regolith of 4 Vesta. We are in the thralls of a collaborative investigation of the record of impact mixing contained within howardites, which includes studies of their mineralogy, petrology, bulk rock compositions, and bulk rock and clast noble gas contents. One goal of our investigation is to test the hypothesis that some howardites represent breccias formed from an ancient, well-mixed regolith on Vesta. Another is to use our results to further understand regolith processing on differentiated asteroids as compared to what has been learned from the Moon. We have made petrographic observations and electron microprobe analyses on 21 howardites and 3 polymict eucrites. We have done bulk rock analyses using X-ray fluorescence spectrometry and are completing inductively coupled plasma mass spectrometry analyses. Here, we discuss our petrologic and bulk compositional results in the context of regolith formation. Companion presentations describe the noble gas results and compositional studies of low-Ca pyroxene clasts

Global Diffusion in a Realistic Three-Dimensional Time-Dependent Nonturbulent Fluid Flow

We introduce and study the first model of an experimentally realizable three-dimensional time-dependent nonturbulent fluid flow to display the phenomenon of global diffusion of passive-scalar particles at arbitrarily small values of the nonintegrable perturbation. This type of chaotic advection, termed {\it resonance-induced diffusion\/}, is generic for a large class of flows.Comment: 4 pages, uuencoded compressed postscript file, to appear in Phys. Rev. Lett. Also available on the WWW from http://formentor.uib.es/~julyan/, or on paper by reques

Noble Gas Analysis in the Quest to Find "Regolithic" Howardites

The howardite meteorites consist of approximately 200 polymict breccias of eucrite (basaltic) and diogenite (orthopyroxenitic) material (collectively, the HED group) that originate from the asteroid belt. Infrared reflectance spectroscopy of asteroids and laboratory studies of HEDs have indicated that the asteroid 4-Vesta is the likely parent body, and the partially-demolished south pole may be the source region. Asteroid regolith formation processes may be responsible for a number of observed petrological features including impact melt clasts, reworked clasts and mosaisicm. We have identified such features in a study of 30 howardites and polymict eucrites, and developed a regolith grading scheme based on petrology. However, the true regolithic nature of the howardite suite is not well defined, and previous research has suggested correlations between Ni contents of 300 - 1200 micron / g, a minimal variation in Al2O3 content around 8-9 wt% and the presence of solar wind noble gases are key hallmarks of an ancient regolith on Vesta . Through combined petrological, compositional and noble gas research, we aim to better understand howardite petrological diversity, regolith formation processes on parent asteroids, and to establish what defines a truly "regolithic" howardite. Our research will play an integral part in the interpretation of data gathered by the Dawn mission. Here we report the preliminary results from our noble gas analyses of four howardites: LEW 85313, EET 99408, MET 96500 and PCA 02066. Bulk major element compositional data have been collected, further petrological data for the HED group are reported by our colleagues, whilst trace-element analyses are underway. Our work will investigate the extent of whether previously described Ni, Al2O3 and noble gas characteristics are in fact indicative of a "regolithic" howardite

Self-Assembling Ice Membranes on Europa: Brinicle Properties, Field Examples, and Possible Energetic Systems in Icy Ocean Worlds

Brinicles are self-assembling tubular ice membrane structures, centimeters to meters in length, found beneath sea ice in the polar regions of Earth. We discuss how the properties of brinicles make them of possible importance for chemistry in cold environments-including that of life's emergence-and we consider their formation in icy ocean world. We argue that the non-ice composition of the ice on Europa and Enceladus will vary spatially due to thermodynamic and mechanical properties that serve to separate and fractionate brines and solid materials. The specifics of the composition and dynamics of both the ice and the ocean in these worlds remain poorly constrained. We demonstrate through calculations using FREZCHEM that sulfate likely fractionates out of accreting ice in Europa and Enceladus, and thus that an exogenous origin of sulfate observed on Europa's surface need not preclude additional endogenous sulfate in Europa's ocean. We suggest that, like hydrothermal vents on Earth, brinicles in icy ocean worlds constitute ideal places where ecosystems of organisms might be found