We obtained Hubble Space Telescope images of 2 Pallas in September 2007 that reveal distinct color and albedo variations across the surface of this large asteroid. Pallas's shape is an ellipsoid with radii of 291 (+/-9), 278 (+/-9), and 250 (+/-9) kilometers, implying a density of 2400 (+/-250) kilograms per cubic meter-a value consistent with a body that formed from water-rich material. Our observations are consistent with the presence of an impact feature, 240 (+/-25) kilometers in diameter, within Pallas's ultraviolet-dark terrain. Our observations imply that Pallas is an intact protoplanet that has undergone impact excavation and probable internal alteration.

The study of binary Kuiper Belt objects helps to probe the dynamic conditions present during planet formation in the solar system. We report on the mutual-orbit determination of 2001 QW322, a Kuiper Belt binary with a very large separation whose properties challenge binary-formation and -evolution theories. Six years of tracking indicate that the binary's mutual-orbit period is approximately 25 to 30 years, that the orbit pole is retrograde and inclined 50 degrees to 62 degrees from the ecliptic plane, and, most surprisingly, that the mutual orbital eccentricity is <0.4. The semimajor axis of 105,000 to 135,000 kilometers is 10 times that of other near-equal-mass binaries. Because this weakly bound binary is prone to orbital disruption by interlopers, its lifetime in its present state is probably less than 1 billion years.

Determination of glucose concentrations in fluids frequently requires the application of immobilized glucose oxidase. An accurate description of the immobilized enzyme kinetics is critical for such applications. In this study, the overall rate of reaction of immobilized glucose oxidase is investigated theoretically. A novel steady-state model based on a ping-pong kinetic mechanism for glucose oxidase is developed. Numerical studies are used to examine the parameter sensitivity of this model. The enzyme loading, matrix thickness and geometric con figuration are found to have a significant influence on substrate uptake by insolubilized glucose oxidase.Aditionally, this new model is compared with a previously developed model based on an alternative ping-pong kinetic mechanism. Under steady-state conditions, no significant difference between the two models is apparent when appropriate kinetic parameters are applied to each of the models. The model developed herein is also compared with models utilizing the simplifying assumption of Michaelis-Mented kinetics for substrate reaction. Numerical studies indicate that under most realizable biological conditions, a model based on ping-pong kinetics should be applied to accurately describe substrate uptake by immobilized glucose oxidase.

The New Horizons (NH) spacecraft observed Io's aurora in eclipse on four occasions during spring 2007. NH Alice ultraviolet spectroscopy and concurrent Hubble Space Telescope ultraviolet imaging in eclipse investigate the relative contribution of volcanoes to Io's atmosphere and its interaction with Jupiter's magnetosphere. Auroral brightness and morphology variations after eclipse ingress and egress reveal changes in the relative contribution of sublimation and volcanic sources to the atmosphere. Brightnesses viewed at different geometries are best explained by a dramatic difference between the dayside and nightside atmospheric density. Far-ultraviolet aurora morphology reveals the influence of plumes on Io's electrodynamic interaction with Jupiter's magnetosphere. Comparisons to detailed simulations of Io's aurora indicate that volcanoes supply 1 to 3% of the dayside atmosphere.

Observations of Jupiter's nightside airglow (nightglow) and aurora obtained during the flyby of the New Horizons spacecraft show an unexpected lack of ultraviolet nightglow emissions, in contrast to the case during the Voyager flybys in 1979. The flux and average energy of precipitating electrons generally decrease with increasing local time across the nightside, consistent with a possible source region along the dusk flank of Jupiter's magnetosphere. Visible emissions associated with the interaction of Jupiter and its satellite Io extend to a surprisingly high altitude, indicating localized low-energy electron precipitation. These results indicate that the interaction between Jupiter's upper atmosphere and near-space environment is variable and poorly understood; extensive observations of the day side are no guide to what goes on at night.

The accretion of bodies in the asteroid belt was halted nearly 4.6 billion years ago by the gravitational influence of the newly formed giant planet Jupiter. The asteroid belt therefore preserves a record of both this earliest epoch of Solar System formation and variation of conditions within the solar nebula. Spectral features in reflected sunlight indicate that some asteroids have experienced sufficient thermal evolution to differentiate into layered structures. The second most massive asteroid--4 Vesta--has differentiated to a crust, mantle and core. 1 Ceres, the largest and most massive asteroid, has in contrast been presumed to be homogeneous, in part because of its low density, low albedo and relatively featureless visible reflectance spectrum, similar to carbonaceous meteorites that have suffered minimal thermal processing. Here we show that Ceres has a shape and smoothness indicative of a gravitationally relaxed object. Its shape is significantly less flattened than that expected for a homogeneous object, but is consistent with a central mass concentration indicative of differentiation. Possible interior configurations include water-ice-rich mantles over a rocky core.

We report 2 cases in which an Artisan phakic intraocular lens (IOL)(Ophtec) was used to successfully treat high myopia after penetrating keratoplasty (PKP). The first case was a 43-year-old man who had a manifest refraction of -13.75 +3.00 x 50 with a best corrected visual acuity (BCVA) of 20/40(-2) after PKP in the left eye. Approximately 9 months after implantation of the Artisan IOL, the manifest refraction was -2.00 +2.50 x 60 with a BCVA of 20/30(+2). The second case was a 31-year-old man who had a manifest refraction of -10.75 +2.25 x 122 and a BCVA of 20/40 after corneal transplantation in the right eye. Ten months after implantation of the Artisan IOL, the manifest refraction was -2.75 +4.75 x 80 with a BCVA of 20/40. Endothelial cell density did not change significantly in either patient after surgery. The Artisan phakic IOL may provide an alternative method to correct high myopia after PKP.