Transport of dust across the Solar System: Constraints on the spatial origin of individual micrometeorites from cosmic-ray exposure.

The origin of micrometeorites (MMs) from asteroids and comets is well-established, but the relative contribution from these two classes remains poorly resolved. Likewise, determining the precise origin of individual MMs is an open challenge. Here, cosmic-ray exposure ages are used to resolve the spatial origins of 12 MMs collected from urban areas and Antarctica. Their 26Al and 10Be concentration, produced during cosmic-ray irradiation in space, were measured by accelerator mass spectrometry. These data are compared to results from a model simulating the transport and irradiation of the MM precursors in space. This model, for the first time, considers a variety of orbits, precursor particle sizes, compositions and densities and incorporates non-isotropic solar and galactic cosmic-ray flux profiles, depth-dependent production rates, as well as spherical evaporation during atmospheric entry. While the origin for six MMs remains ambiguous, two MMs show a preferential tendency towards an origin in the Inner Solar System (Near Earth Objects to the Asteroid Belt) and four towards an origin in the Outer Solar System (Jupiter Family Comets to the Kuiper Belt). These findings challenge the notion that dust originating from the Outer Solar System is unlikely to survive long-term transport and delivery to the terrestrial planets. This article is part of the theme issue 'Dust in the Solar System and beyond'.

Isotopic evolution of planetary crusts by hypervelocity impacts evidenced by Fe in microtektites.

Fractionation effects related to evaporation and condensation had a major impact on the current elemental and isotopic composition of the Solar System. Although isotopic fractionation of moderately volatile elements has been observed in tektites due to impact heating, the exact nature of the processes taking place during hypervelocity impacts remains poorly understood. By studying Fe in microtektites, here we show that impact events do not simply lead to melting, melt expulsion and evaporation, but involve a convoluted sequence of processes including condensation, variable degrees of mixing between isotopically distinct reservoirs and ablative evaporation during atmospheric re-entry. Hypervelocity impacts can as such not only generate isotopically heavy, but also isotopically light ejecta, with δ56/54Fe spanning over nearly 5‰ and likely even larger variations for more volatile elements. The mechanisms demonstrated here for terrestrial impact ejecta modify our understanding of the effects of impact processing on the isotopic evolution of planetary crusts.

A large meteoritic event over Antarctica ca. 430 ka ago inferred from chondritic spherules from the Sør Rondane Mountains.

Large airbursts, the most frequent hazardous impact events, are estimated to occur orders of magnitude more frequently than crater-forming impacts. However, finding traces of these events is impeded by the difficulty of identifying them in the recent geological record. Here, we describe condensation spherules found on top of Walnumfjellet in the Sør Rondane Mountains, Antarctica. Affinities with similar spherules found in EPICA Dome C and Dome Fuji ice cores suggest that these particles were produced during a single-asteroid impact ca. 430 thousand years (ka) ago. The lack of a confirmed crater on the Antarctic ice sheet and geochemical and 18O-poor oxygen isotope signatures allow us to hypothesize that the impact particles result from a touchdown event, in which a projectile vapor jet interacts with the Antarctic ice sheet. Numerical models support a touchdown scenario. This study has implications for the identification and inventory of large cosmic events on Earth.

A new biological glue for cartilage-cartilage interfaces: tissue transglutaminase.

In this study, we used an in vitro model to test the capacity of tissue transglutaminase to increase the adhesive strength at a cartilage-cartilage interface. Full-thickness cartilage-bone cylinders were prepared from fresh adult bovine shoulder joints, and the superficial half of the hyaline cartilage was then removed to provide a plane surface. Tissue transglutaminase was applied to the freshly cut surface of one cylinder, and a calcium-chloride solution (to act as an activating agent) was applied to that of the other. The cartilage surfaces were immediately apposed, one on top of the other, and an eighty-gram weight was applied to the upper cylinder for ten minutes at 37 degrees Celsius under defined humidity conditions. A measured force was then applied transversely to the upper cylinder until it was displaced from the lower one (which was clamped in a holding device), and the force recorded at this point was taken as a measure of the adhesive strength achieved at the cartilage-cartilage interface. The adhesive strength increased linearly with an increasing concentration of tissue transglutaminase (0.25 to 2.75 milligrams per milliliter) and was enhanced by increasing the duration of incubation, but it was not influenced by the level of humidity. The adhesive strength was improved by as much as 40 per cent when the cartilage surfaces had been pretreated with chondroitinase AC or hyaluronidase to remove glycosaminoglycan chains of proteoglycans, which are largely responsible for the intrinsic anti-adhesive properties of cartilage.

Loads acting in an intramedullary nail during fracture healing in the human femur.

The form and function of the musculo-skeletal system is closely related to the forces acting in its components. Significant forces are present in the long bones, but their magnitudes have so far only been estimated from mathematical models. Fracture fixation by means of metal implants provides an opportunity to measure the implant-born forces and to estimate the long bone forces before healing occurs. The load changes during fracture healing may provide additional information. Therefore, a telemetrized, interlocking femoral nail for wireless transmission of forces and moments acting across the fracture site was developed. The design was based on the geometry and material of a 16 mm AO nail with a circular, closed cross-section allowing full protection of the electronic circuits from the body fluids. After careful testing, it was implanted in a 33-year-old patient who had sustained a multifragmentary fracture of the left femur. Measurements at a rate of approx. 0.4 Hz were performed in different patient postures between the 2nd and 26th postoperative week. Significant axial forces and bending moments were measured during several activities such as sitting, unsupported leg elevation and partial weight bearing in a standing position. Forces orthogonal to the nail axis remained small. The reductions of the implant loads due to fracture consolidation were in the order of 50%. Dynamization of the nail did not change the forces. Even though the telemetry system did not allow for dynamic measurements and the results presented here provide data from one subject only, the new information will be useful with respect to implant design, biomechanics of fracture fixation and evaluation of healing progression.

Contrast material-induced renal failure in patients with diabetes mellitus, renal insufficiency, or both. A prospective controlled study.

To determine the risk of nephrotoxicity induced by the infusion of radiographic contrast material, we undertook a prospective study of consecutive patients undergoing radiographic procedures with intravascular contrast material. There were three study groups: patients with diabetes mellitus and normal renal function (n = 85), patients with preexisting renal insufficiency (serum creatinine level, greater than or equal to 150 mumol per liter) without diabetes (n = 101), and patients with both diabetes and renal insufficiency (n = 34). The control group consisted of patients undergoing CT scanning or abdominal imaging procedures without the infusion of contrast material who had diabetes mellitus (n = 59), preexisting renal insufficiency (n = 145), or both (n = 64). Clinically important acute renal failure (defined as an increase of greater than 50 percent in the serum creatinine level) attributable to the contrast material did not occur in nondiabetic patients with preexisting renal insufficiency or in diabetics with normal renal function. The incidence of clinically important contrast-induced renal failure among the diabetic patients with preexisting renal insufficiency was 8.8 percent (95 percent confidence interval, 1.9 to 23.7 percent), as compared with 1.6 percent for the controls. The incidence of acute renal insufficiency, more broadly defined as an increase of greater than 25 percent in the serum creatinine level after the infusion of contrast material, was 11.8 percent among all patients with preexisting renal insufficiency. After the exclusion of patients whose acute renal insufficiency could be attributed to other causes, the incidence was 7.0 percent (95 percent confidence interval, 3.2 to 12.8 percent), as compared with 1.5 percent in the control group. The risk of acute renal insufficiency attributable to the contrast material was therefore 5.5 percent, and the relative risk associated with the infusion of contrast material was 4.7. These rates were similar whether the osmolarity of the contrast material was high or low. We conclude that there is little risk of clinically important nephrotoxicity attributable to contrast material for patients with diabetes and normal renal function or for nondiabetic patients with preexisting renal insufficiency. The risk for those with both diabetes and preexisting renal insufficiency is about 9 percent, which is lower than previously reported.

Possible in situ formation of meteoritic nanodiamonds in the early Solar System.

Grains of dust that pre-date the Sun provide insights into their formation around other stars and into the early evolution of the Solar System. Nanodiamonds recovered from meteorites, which originate in asteroids, have been thought to be the most abundant type of presolar grain. If that is true, then nanodiamonds should be at least as abundant in comets, because they are thought to have formed further out in the early Solar System than the asteroid parent bodies, and because they should be more pristine. Here we report that nanodiamonds are absent or very depleted in fragile, carbon-rich interplanetary dust particles, some of which enter the atmosphere at speeds within the range of cometary meteors. One interpretation of the results is that some (perhaps most) nanodiamonds formed within the inner Solar System and are not presolar at all, consistent with the recent detection of nanodiamonds within the accretion discs of other young stars. An alternative explanation is that all meteoritic nanodiamonds are indeed presolar, but that their abundance decreases with heliocentric distance, in which case our understanding of large-scale transport and circulation within the early Solar System is incomplete.