Fast boulder fracturing by thermal fatigue detected on stony asteroids.

Spacecraft observations revealed that rocks on carbonaceous asteroids, which constitute the most numerous class by composition, can develop millimeter-to-meter-scale fractures due to thermal stresses. However, signatures of this process on the second-most populous group of asteroids, the S-complex, have been poorly constrained. Here, we report observations of boulders' fractures on Dimorphos, which is the moonlet of the S-complex asteroid (65803) Didymos, the target of NASA's Double Asteroid Redirection Test (DART) planetary defense mission. We show that the size-frequency distribution and orientation of the mapped fractures are consistent with formation through thermal fatigue. The fractures' preferential orientation supports that these have originated in situ on Dimorphos boulders and not on Didymos boulders later transferred to Dimorphos. Based on our model of the fracture propagation, we propose that thermal fatigue on rocks exposed on the surface of S-type asteroids can form shallow, horizontally propagating fractures in much shorter timescales (100 kyr) than in the direction normal to the boulder surface (order of Myrs). The presence of boulder fields affected by thermal fracturing on near-Earth asteroid surfaces may contribute to an enhancement in the ejected mass and momentum from kinetic impactors when deflecting asteroids.

The Dimorphos ejecta plume properties revealed by LICIACube.

The Double Asteroid Redirection Test (DART) had an impact with Dimorphos (a satellite of the asteroid Didymos) on 26 September 20221. Ground-based observations showed that the Didymos system brightened by a factor of 8.3 after the impact because of ejecta, returning to the pre-impact brightness 23.7 days afterwards2. Hubble Space Telescope observations made from 15 minutes after impact to 18.5 days after, with a spatial resolution of 2.1 kilometres per pixel, showed a complex evolution of the ejecta3, consistent with other asteroid impact events. The momentum enhancement factor, determined using the measured binary period change4, ranges between 2.2 and 4.9, depending on the assumptions about the mass and density of Dimorphos5. Here we report observations from the LUKE and LEIA instruments on the LICIACube cube satellite, which was deployed 15 days in advance of the impact of DART. Data were taken from 71 seconds before the impact until 320 seconds afterwards. The ejecta plume was a cone with an aperture angle of 140 ± 4 degrees. The inner region of the plume was blue, becoming redder with increasing distance from Dimorphos. The ejecta plume exhibited a complex and inhomogeneous structure, characterized by filaments, dust grains and single or clustered boulders. The ejecta velocities ranged from a few tens of metres per second to about 500 metres per second.

The geology and geophysics of Kuiper Belt object (486958) Arrokoth.

The Cold Classical Kuiper Belt, a class of small bodies in undisturbed orbits beyond Neptune, is composed of primitive objects preserving information about Solar System formation. In January 2019, the New Horizons spacecraft flew past one of these objects, the 36-kilometer-long contact binary (486958) Arrokoth (provisional designation 2014 MU69). Images from the flyby show that Arrokoth has no detectable rings, and no satellites (larger than 180 meters in diameter) within a radius of 8000 kilometers. Arrokoth has a lightly cratered, smooth surface with complex geological features, unlike those on previously visited Solar System bodies. The density of impact craters indicates the surface dates from the formation of the Solar System. The two lobes of the contact binary have closely aligned poles and equators, constraining their accretion mechanism.

Initial results from the New Horizons exploration of 2014 MU69, a small Kuiper Belt object.

The Kuiper Belt is a distant region of the outer Solar System. On 1 January 2019, the New Horizons spacecraft flew close to (486958) 2014 MU69, a cold classical Kuiper Belt object approximately 30 kilometers in diameter. Such objects have never been substantially heated by the Sun and are therefore well preserved since their formation. We describe initial results from these encounter observations. MU69 is a bilobed contact binary with a flattened shape, discrete geological units, and noticeable albedo heterogeneity. However, there is little surface color or compositional heterogeneity. No evidence for satellites, rings or other dust structures, a gas coma, or solar wind interactions was detected. MU69's origin appears consistent with pebble cloud collapse followed by a low-velocity merger of its two lobes.

Pluto's Interaction With Energetic Heliospheric Ions.

Pluto energies of a few kiloelectron volts and suprathermal ions with tens of kiloelectron volts and above. We measure this population using the Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) instrument on board the New Horizons spacecraft that flew by Pluto in 2015. Even though the measured ions have gyroradii larger than the size of Pluto and the cross section of its magnetosphere, we find that the boundary of the magnetosphere is depleting the energetic ion intensities by about an order of magnitude close to Pluto. The intensity is increasing exponentially with distance to Pluto and reaches nominal levels of the interplanetary medium at about 190R P distance. Inside the wake of Pluto, we observe oscillations of the ion intensities with a periodicity of about 0.2 hr. We show that these can be quantitatively explained by the electric field of an ultralow-frequency wave and discuss possible physical drivers for such a field. We find no evidence for the presence of plutogenic ions in the considered energy range.

The formation of Charon's red poles from seasonally cold-trapped volatiles.

A unique feature of Pluto's large satellite Charon is its dark red northern polar cap. Similar colours on Pluto's surface have been attributed to tholin-like organic macromolecules produced by energetic radiation processing of hydrocarbons. The polar location on Charon implicates the temperature extremes that result from Charon's high obliquity and long seasons in the production of this material. The escape of Pluto's atmosphere provides a potential feedstock for a complex chemistry. Gas from Pluto that is transiently cold-trapped and processed at Charon's winter pole was proposed as an explanation for the dark coloration on the basis of an image of Charon's northern hemisphere, but not modelled quantitatively. Here we report images of the southern hemisphere illuminated by Pluto-shine and also images taken during the approach phase that show the northern polar cap over a range of longitudes. We model the surface thermal environment on Charon and the supply and temporary cold-trapping of material escaping from Pluto, as well as the photolytic processing of this material into more complex and less volatile molecules while cold-trapped. The model results are consistent with the proposed mechanism for producing the observed colour pattern on Charon.

The small satellites of Pluto as observed by New Horizons.

The New Horizons mission has provided resolved measurements of Pluto's moons Styx, Nix, Kerberos, and Hydra. All four are small, with equivalent spherical diameters of ~40 kilometers for Nix and Hydra and ~10 kilometers for Styx and Kerberos. They are also highly elongated, with maximum to minimum axis ratios of ~2. All four moons have high albedos (~50 to 90%) suggestive of a water-ice surface composition. Crater densities on Nix and Hydra imply surface ages of at least 4 billion years. The small moons rotate much faster than synchronous, with rotational poles clustered nearly orthogonal to the common pole directions of Pluto and Charon. These results reinforce the hypothesis that the small moons formed in the aftermath of a collision that produced the Pluto-Charon binary.

Surface compositions across Pluto and Charon.

The New Horizons spacecraft mapped colors and infrared spectra across the encounter hemispheres of Pluto and Charon. The volatile methane, carbon monoxide, and nitrogen ices that dominate Pluto's surface have complicated spatial distributions resulting from sublimation, condensation, and glacial flow acting over seasonal and geological time scales. Pluto's water ice "bedrock" was also mapped, with isolated outcrops occurring in a variety of settings. Pluto's surface exhibits complex regional color diversity associated with its distinct provinces. Charon's color pattern is simpler, dominated by neutral low latitudes and a reddish northern polar region. Charon's near-infrared spectra reveal highly localized areas with strong ammonia absorption tied to small craters with relatively fresh-appearing impact ejecta.

The Pluto system: Initial results from its exploration by New Horizons.

The Pluto system was recently explored by NASA's New Horizons spacecraft, making closest approach on 14 July 2015. Pluto's surface displays diverse landforms, terrain ages, albedos, colors, and composition gradients. Evidence is found for a water-ice crust, geologically young surface units, surface ice convection, wind streaks, volatile transport, and glacial flow. Pluto's atmosphere is highly extended, with trace hydrocarbons, a global haze layer, and a surface pressure near 10 microbars. Pluto's diverse surface geology and long-term activity raise fundamental questions about how small planets remain active many billions of years after formation. Pluto's large moon Charon displays tectonics and evidence for a heterogeneous crustal composition; its north pole displays puzzling dark terrain. Small satellites Hydra and Nix have higher albedos than expected.

Jupiter cloud composition, stratification, convection, and wave motion: a view from new horizons.

Several observations of Jupiter's atmosphere made by instruments on the New Horizons spacecraft have implications for the stability and dynamics of Jupiter's weather layer. Mesoscale waves, first seen by Voyager, have been observed at a spatial resolution of 11 to 45 kilometers. These waves have a 300-kilometer wavelength and phase velocities greater than the local zonal flow by 100 meters per second, much higher than predicted by models. Additionally, infrared spectral measurements over five successive Jupiter rotations at spatial resolutions of 200 to 140 kilometers have shown the development of transient ammonia ice clouds (lifetimes of 40 hours or less) in regions of strong atmospheric upwelling. Both of these phenomena serve as probes of atmospheric dynamics below the visible cloud tops.

Io's atmospheric response to eclipse: UV aurorae observations.

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.

New horizons mapping of Europa and Ganymede.

The New Horizons spacecraft observed Jupiter's icy satellites Europa and Ganymede during its flyby in February and March 2007 at visible and infrared wavelengths. Infrared spectral images map H2O ice absorption and hydrated contaminants, bolstering the case for an exogenous source of Europa's "non-ice" surface material and filling large gaps in compositional maps of Ganymede's Jupiter-facing hemisphere. Visual wavelength images of Europa extend knowledge of its global pattern of arcuate troughs and show that its surface scatters light more isotropically than other icy satellites.

Io volcanism seen by new horizons: a major eruption of the Tvashtar volcano.

Jupiter's moon Io is known to host active volcanoes. In February and March 2007, the New Horizons spacecraft obtained a global snapshot of Io's volcanism. A 350-kilometer-high volcanic plume was seen to emanate from the Tvashtar volcano (62 degrees N, 122 degrees W), and its motion was observed. The plume's morphology and dynamics support nonballistic models of large Io plumes and also suggest that most visible plume particles condensed within the plume rather than being ejected from the source. In images taken in Jupiter eclipse, nonthermal visible-wavelength emission was seen from individual volcanoes near Io's sub-Jupiter and anti-Jupiter points. Near-infrared emission from the brightest volcanoes indicates minimum magma temperatures in the 1150- to 1335-kelvin range, consistent with basaltic composition.

The rubble-pile asteroid Itokawa as observed by Hayabusa.

During the interval from September through early December 2005, the Hayabusa spacecraft was in close proximity to near-Earth asteroid 25143 Itokawa, and a variety of data were taken on its shape, mass, and surface topography as well as its mineralogic and elemental abundances. The asteroid's orthogonal axes are 535, 294, and 209 meters, the mass is 3.51 x 10(10) kilograms, and the estimated bulk density is 1.9 +/- 0.13 grams per cubic centimeter. The correspondence between the smooth areas on the surface (Muses Sea and Sagamihara) and the gravitationally low regions suggests mass movement and an effective resurfacing process by impact jolting. Itokawa is considered to be a rubble-pile body because of its low bulk density, high porosity, boulder-rich appearance, and shape. The existence of very large boulders and pillars suggests an early collisional breakup of a preexisting parent asteroid followed by a re-agglomeration into a rubble-pile object.

Evaluation of the BD Phoenix Automated Microbiology System for identification and antimicrobial susceptibility testing of common clinical isolates.

OBJECTIVE: To evaluate the accuracy and reliability of the BD Phoenix Automated Microbiology System for identification (ID) and antimicrobial susceptibility testing (AST) of Gram-positive and Gram-negative isolates. MATERIALS AND METHODS: The ID of 291 Gram-negative and 158 Gram-positive clinical isolates were evaluated by the system. The AST of 252 Gram-negative and 151 Gram-positive isolates with correct ID were then evaluated. The results were compared with those of the API ID system and the microbroth dilution method. All discrepant results were repeated for verification. RESULTS: Over 90% Gram-negative and Gram-positive isolates were correctly identified to species or genus level by the Phoenix system. The minimum inhibitory concentration agreement rates between the Phoenix and the microbroth dilution methods within +/-1 dilution ranged from 87.3 to 97.6% for Gram-negative isolates, and from 50 to 100% for Gram-positive isolates. For Gram-positive isolates, vancomycin had significant low minimum inhibitory concentration agreement rates. CONCLUSIONS: Overall, the results indicate that the Phoenix system is a reliable system. It could provide accurate ID and AST results for routine clinical laboratories.

Dynamics of Saturn's magnetosphere from MIMI during Cassini's orbital insertion.

The Magnetospheric Imaging Instrument (MIMI) onboard the Cassini spacecraft observed the saturnian magnetosphere from January 2004 until Saturn orbit insertion (SOI) on 1 July 2004. The MIMI sensors observed frequent energetic particle activity in interplanetary space for several months before SOI. When the imaging sensor was switched to its energetic neutral atom (ENA) operating mode on 20 February 2004, at approximately 10(3) times Saturn's radius RS (0.43 astronomical units), a weak but persistent signal was observed from the magnetosphere. About 10 days before SOI, the magnetosphere exhibited a day-night asymmetry that varied with an approximately 11-hour periodicity. Once Cassini entered the magnetosphere, in situ measurements showed high concentrations of H+, H2+, O+, OH+, and H2O+ and low concentrations of N+. The radial dependence of ion intensity profiles implies neutral gas densities sufficient to produce high loss rates of trapped ions from the middle and inner magnetosphere. ENA imaging has revealed a radiation belt that resides inward of the D ring and is probably the result of double charge exchange between the main radiation belt and the upper layers of Saturn's exosphere.

Combined use of alcohol hand rub and gloves reduces the incidence of late onset infection in very low birthweight infants.

OBJECTIVE: To assess the incidence of late onset (> 72 hours) infection and necrotising enterocolitis (NEC) in very low birthweight (VLBW) infants in two 36 month periods using two hand hygiene protocols: conventional handwashing (HW; first 36 month period); an alcohol hand rub and gloves technique (HR; second 36 month period). METHOD: VLBW infants admitted to the neonatal intensive care unit during the period December 1993-November 1999 were eligible. A new hand hygiene protocol using alcohol handrub and gloves was introduced in December 1996. Each patient's case record was reviewed retrospectively by two independent investigators using a standard data collection form. The incidence of NEC and systemic infections, including bacterial or fungal septicaemia, meningitis, and peritonitis, in the two periods were compared. RESULTS: The HW and HR groups contained 161 and 176 VLBW infants respectively. The incidence of late onset systemic infection decreased from 13.5 to 4.8 episodes (including NEC)/1000 patient days after introduction of the HR regimen, representing a 2.8-fold reduction. Similarly, the incidence of Gram positive, Gram negative, and fungal infections decreased 2.5-fold, 2.6-fold, and 7-fold respectively. There was also a significant reduction in the incidence of NEC in the HR group (p < 0.0001). Subgroup analysis revealed that the incidence of methicillin resistant Staphylococcus aureus (MRSA) septicaemia was significantly decreased in the second 36 month period (p = 0.048). The clinical data suggest that infants in the HW group had significantly earlier onset of sepsis (p < 0.05) and required oxygen supplementation for longer (p < 0.05) than those in the HR group. Significantly more VLBW infants were discharged from the neonatal intensive care unit without ever being infected (p < 0.0001), and also significantly fewer infants had more than one episode of infection in the HR group (p < 0.0001). CONCLUSION: The introduction of the HR protocol was associated with a 2.8-fold reduction in the incidence of late onset systemic infection, and also a significant decrease in the incidence of MRSA septicaemia and NEC in VLBW infants. This decrease in infection rate was maintained throughout the second 36 month period.

A longitudinal analysis of methicillin-resistant Staphylococcus aureus in a Hong Kong teaching hospital.

OBJECTIVES: To review the incidence and trends of MRSA during a 12-year (1989-2000) period at a university teaching hospital and the relationship between strain distribution by antibiogram and molecular typing. DESIGN: Retrospective review of laboratory-based surveillance records on MRSA isolation and characterization of strains by antimicrobial susceptibility and PFGE. A patient episode was counted at the time when MRSA was first isolated. SETTING: A 1,350-bed university teaching hospital in Hong Kong. PATIENTS: Those with clinical isolates of MRSA. RESULTS: During 1989 to 2000, the hospital recorded 1,203,175 deaths and discharges (D&D) and encountered 5,707 patient episodes of new MRSA isolation. The overall incidence of patient episodes of MRSA was 0.47/100 D&D. In 1989, the incidence was 0.81/100 D&D and fell to a low of 0.33/100 D&D in 1995, but then rose to 0.50/100 D&D in 2000. Antibiogram and DNA typing identified 5 major types. PFGE type A constituted 68% (211/312) of isolates and was present throughout the 12-year period. PFGE type B constituted 13% (40/312) of isolates and was only present from 1995 to 2000. These isolates form a distinct clone and had unique antibiotic resistance profiles. CONCLUSIONS: The study showed the establishment of a dominant MRSA clone (PFGE type A group) in the intensive care, medical, and surgical units and the appearance of a new MRSA strain in 1995 (PFGE type B), which partly explained the rise in incidence of MRSA cases and a disproportionate rise in MRSA bacteremia from 1995 to 2000.

An in vitro study on the compatibility and precipitation of a combination of ciprofloxacin and vancomycin in human vitreous.

AIMS: To investigate the precipitation process of a mixture of vancomycin and ciprofloxacin by equilibrium dialysis and its subsequent effect on the level of available free antibiotics. METHODS: Concentrations of vancomycin and ciprofloxacin in an equilibrium dialysis chamber were measured during the equilibrium process by high performance liquid chromatography and fluorescence polarisation immunoassay. Normal saline (NS), balanced salt solution plus (BSS Plus), and vitreous were used separately as the medium of dialysis. RESULTS: Precipitation of ciprofloxacin occurred on incubation at 37 degrees C. It formed precipitate on its own or when mixed with vancomycin in all the three media of NS, BSS Plus, and vitreous. There was more precipitation at higher initial ciprofloxacin concentrations; at 25.0 mg/l about 75% free drug in BSS Plus was lost after 72 hours. The extent of precipitation was similar in both NS and BSS Plus. In the dialysis chambers, 20 mg/l ciprofloxacin dialysed against 125 mg/l vancomycin was reduced to a concentration about 5.0 mg/l after 168 hours. Precipitation of vancomycin was negligible. Ciprofloxacin precipitated in vitreous at body temperature, irrespective of the presence of vancomycin. Even after precipitation, the resultant concentration of ciprofloxacin was still higher than the MIC(90) of the drug against most Gram negative organisms. CONCLUSIONS: Based on this in vitro study, ciprofloxacin precipitated in vitreous at body temperature, irrespective of the presence of vancomycin or the medium for intravitreal injection. The resultant amount of ciprofloxacin was still higher than the MIC(90) of the drug against most Gram negative organisms after precipitation. The authors suggest ciprofloxacin in place of ceftazidime when used in combination with vancomycin for treatment of infective endophthalmitis.

Pertussis--a re-emerging infection?

Seven cases of pertussis in patients aged between 1 and 6 months detected over 3 months were reported. Paroxysmal cough (six cases), post-tussive vomiting (three cases) and poor feeding (three cases) were the most common presenting symptoms. Bordetella pertussis was isolated from six patients. The total leucocyte counts were mildly increased (10.8-15.6x10(9)/L). The lymphocyte counts were markly raised (59-73%) and appear to be useful indicators of pertussis. It appears that herd immunity does not offer adequate protection to the vulnerable group even in well-vaccinated populations. High vaccination coverage should be maintained, and vaccination should be given as early an age as possible. Aggressive efforts to identify cases and contacts are essential. Health care workers should have a high index of suspicion for pertussis, in particular for those with paroxysmal cough and high lymphocyte counts so as to give timely diagnosis and treatment.