Discovery of diffuse aurora on Mars.

Planetary auroras reveal the complex interplay between an atmosphere and the surrounding plasma environment. We report the discovery of low-altitude, diffuse auroras spanning much of Mars' northern hemisphere, coincident with a solar energetic particle outburst. The Imaging Ultraviolet Spectrograph, a remote sensing instrument on the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, detected auroral emission in virtually all nightside observations for ~5 days, spanning nearly all geographic longitudes. Emission extended down to ~60 kilometer (km) altitude (1 microbar), deeper than confirmed at any other planet. Solar energetic particles were observed up to 200 kilo--electron volts; these particles are capable of penetrating down to the 60 km altitude. Given minimal magnetic fields over most of the planet, Mars is likely to exhibit auroras more globally than Earth.

Water vapour jets inside the plume of gas leaving Enceladus.

A plume of water vapour escapes from fissures crossing the south polar region of the Saturnian moon Enceladus. Tidal deformation of a thin surface crust above an internal ocean could result in tensile and compressive stresses that would affect the width of the fissures; therefore, the quantity of water vapour released at different locations in Enceladus' eccentric orbit is a crucial measurement of tidal control of venting. Here we report observations of an occultation of a star by the plume on 24 October 2007 that revealed four high-density gas jets superimposed on the background plume. The gas jet positions coincide with those of dust jets reported elsewhere inside the plume. The maximum water column density in the plume is about twice the density reported earlier. The density ratio does not agree with predictions-we should have seen less water than was observed in 2005. The ratio of the jets' bulk vertical velocities to their thermal velocities is 1.5 +/- 0.2, which supports the hypothesis that the source of the plume is liquid water, with gas accelerated to supersonic velocity in nozzle-like channels.

Structure and vibrational dynamics of model compounds of the [FeFe]-hydrogenase enzyme system via ultrafast two-dimensional infrared spectroscopy.

Ultrafast two-dimensional infrared (2D) spectroscopy has been applied to study the structure and vibrational dynamics of (mu-S(CH2)3S)Fe2(CO)6, a model compound of the active site of the [FeFe]-hydrogenase enzyme system. Comparison of 2D-IR spectra of (mu-S(CH2)3S)Fe2(CO)6 with density functional theory calculations has determined that the solution-phase structure of this molecule is similar to that observed in the crystalline phase and in good agreement with gas-phase simulations. In addition, vibrational coupling and rapid (<5 ps) solvent-mediated equilibration of energy between vibrationally excited states of the carbonyl ligands of the di-iron-based active site model are observed prior to slower (approximately 100 ps) relaxation to the ground state. These dynamics are shown to be solvent-dependent and form a basis for the future determination of the vibrational interactions between active site and protein.

Enceladus' water vapor plume.

The Cassini spacecraft flew close to Saturn's small moon Enceladus three times in 2005. Cassini's UltraViolet Imaging Spectrograph observed stellar occultations on two flybys and confirmed the existence, composition, and regionally confined nature of a water vapor plume in the south polar region of Enceladus. This plume provides an adequate amount of water to resupply losses from Saturn's E ring and to be the dominant source of the neutral OH and atomic oxygen that fill the Saturnian system.

The central Scotland Escherichia coli O157:H7 outbreak: risk factors for the hemolytic uremic syndrome and death among hospitalized patients.

Little is known about risk factors for complications of Escherichia coli O157:H7 infection in adults. The 1996 outbreak in central Scotland involved the largest number of adult case patients in whom hemolytic uremic syndrome (HUS) developed and, ultimately, the largest number of deaths associated with E. coli O157:H7 infection that has yet been recorded. We investigated risk factors for HUS in a retrospective study of all hospitalized case patients in this outbreak. Of 120 case patients, 34 had HUS develop, 28 of whom were adults. Sixteen adults died. Significant risk factors for HUS were age <15 years or >65 years (odds ratio [OR], 4.4; 95% confidence interval [CI], 1.3-14.4), hypochlorhydria (OR, 6.7; 95% CI, 1.9-24.0), and coincidental antibiotics (OR, 4.7; 95% CI 1.4-16.5). Factors associated with HUS were as follows: white blood cell count >20 x 10(9) cells/L (OR, 8.25; 95% CI, 1.1-60.3), neutrophil count >15 x 10(9) cells/L (OR, 8.5; 95% CI, 1.5-50.1), and serum albumin level <35 g/L (OR, 7.2; 95% CI, 1.2-42.5) < or =3 days after symptom onset. Deaths were confined to case patients >65 years of age. Early identification of risk factors for HUS is vital and could select case patients for trials of preventative and treatment therapies.

Galileo ultraviolet spectrometer experiment: initial venus and interplanetary cruise results.

The Galileo Extreme Ultraviolet Spectrometer obtained a spectrum of Venus atmospheric emissions in the 55.0- to 125.0-nanometer (nm) wavelength region. Emissions of helium (58.4 nm), ionized atomic oxygen (83.4 nm), and atomic hydrogen (121.6 nm), as well as a blended spectral feature of atomic hydrogen (Lyman-beta) and atomic oxygen (102.5 nm), were observed at 3.5-nm resolution. During the Galileo spacecraft cruise from Venus to Earth, Lyman-alpha emission from solar system atomic hydrogen (121.6 nm) was measured. The dominant source of the Lyman-alpha emission is atomic hydrogen from the interstellar medium. A model of Galileo observations at solar maximum indicates a decrease in the solar Lyman-alpha flux near the solar poles. A strong day-to-day variation also occurs with the 27-day periodicity of the rotation of the sun.

Analysis of the Pioneer-Venus Lyman-agr Image of the Hydrogen Coma of Comet P/Halley.

Comet Halley passed within 0.27 astronomical unit of Venus on 4 February 1986, 5 days before perihelion. This provided a unique opportunity to observe the comet's coma with the ultraviolet spectrometer orbiting the planet aboard the Pioneer Venus Orbiter spacecraft when the coma was otherwise obscured from Earth's view by the sun's glare. More than 9000 data points acquired systematically over the 5-day period from 2 to 6 February were combined to construct an excellent Lyman-alpha image of the hydrogen coma. The Lyman-alpha image was successfully reproduced with a comprehensive physical model, thereby verifying and documenting the underlying chemical kinetics and dynamics of the hydrogen coma.

Ultraviolet night airglow of venus.

The night airglow spectrum of Venus in the ultraviolet is dominated by the v' = 0 progressions of the gamma and delta bands of nitric oxide. The bands are produced by two-body radiative recombination of nitrogen and oxygen atoms. Since the source of these atoms is in the dayside thermosphere, the night airglow is a tracer of the day-to-night thermospheric circulation. The airglow is brightest at equatorial latitudes, and at longitudes on the morning side of the antisolar meridian.

Nature of the ultraviolet absorber in the venus clouds: inferences based on pioneer venus data.

Several photometric measurements of Venus made from the Pioneer Venus orbiter and probes indicate that solar near-ultraviolet radiation is being absorbed throughout much of the main cloud region, but little above the clouds or within the first one or two optical depths. Radiative transfer calculations were carried out to simulate both Pioneer Venus and ground-based data for a number of proposed cloud compositions. This comparison rules out models invoking nitrogen dioxide, meteoritic material, and volatile metals as the source of the ultraviolet absorption. Models involving either small ( approximately 1 micrometer) or large ( approximately 10 micrometers) sulfur particles have some serious difficulties, while ones invoking sulfur dioxide gas appear to be promising.

Ultraviolet spectroscopy of venus: initial results from the pioneer venus orbiter.

Ultraviolet spectroscopy of the Venus cloud tops reveals absorption features attributed to sulfur dioxide in the atmosphere above the cloud tops. Measurements of scattered sunlight at 2663 angstroms show evidence for horizontal and vertical inhomogeneities in cloud structure. Images of the planet at SO(2) absorption wavelengths show albedo features similar to those seen at 3650 angstroms from Mariner 10. Airglowv emissions are consistent with an exospheric temperatuire of approximately 275 K, and a night airglows emission has been detected, indicating the precipitation of energy into the dark thermosphere.

Mariner 9 ultraviolet spectrometer experiment: seasonal variation of ozone on Mars.

Ozone is observed to be present in the polar regions of Mars and to have a seasonal variation. In the summer, the amount present in the polar atmosphere is less than 3 micrometer-atmospheres. In the fall, ozone increases in amount and is found in association with the formation of the polar hood. In winter, the maximum amount of ozone is present, 57 micrometer-atmospheres over the polar hood and 16 over the polar cap. In spring, the amount over the polar cap decreases monotonically until by the beginning of summer the ozone disappears. Ozone is not observed in the equatorial region during any season.

Mariner 9 ultraviolet spectrometer experiment: initial results.

The ultraviolet airglow spectrum of Mars has been measured from an orbiting spacecraft during a 30-day period in November-December 1971. The emission rates of the carbon monoxide Cameron and fourth positive bands, the atomic oxygen 1304-angstrom line and the atomic hydrogen 1216-angstrom line have been measured as a function of altitude. Significant variations in the scale height of the CO Cameron band airglow have been observed during a period of variable solar activity; however, the atomic oxygen and hydrogen airglow lines are present during all the observations. Measurements of the reflectance of the lower atmosphere of Mars show the spectral characteristics of particle scattering and a magnitude that is about 50 percent of that measured during the Mariner 6 and 7 experiments in 1969. The variation of reflectance across the planet may be represented by a model in which the dominant scatterer is dust that absorbs in the ultraviolet and has an optical depth greater than 1. The atmosphere above the polar region is clearer than over the rest of the planet.

Mariner 6: origin of Mars ionized carbon dioxide ultraviolet spectrum.

The predicted intensities of the ionized carbon dioxide (CO(2)+) emission feature at 2890 angstroms and the Fox-Duffendack-Barker bands are 5.2 and 19.9 kilorayleighs, respectively, for a vertical column. Direct photoionization of carbon dioxide by solar radiation contributes 3.5 and 4.1 kilorayleighs, respectively, and fluorescent scattering by C0(2)+, 1.6 and 15.3 kilorayleighs, respectively. Photoelectron impacts are less important.

Mariner 6: ultraviolet spectrum of Mars upper atmosphere.

Emission features from ionized carbon dioxide and carbon monoxide were measured in the 1900- to 4300-angstrom spectral region. The Lyman alpha 1216-angstrom line of atomic hydrogen and the 1304-, 1356-, and 2972-angstrom lines of atomic oxygen were observed.