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Nanophase materials can result in harder metals, but more brittle. However it is still reasonable to expected that nanometre-scale composite materials may be better than conventional composites. Researchers have discussed the challenges of making nanocomposites at a conference in Alaska, and concluded that inputs from several fields would be required to make it work. Nanotubes and nanoparticles are simple systems for molecular modellers and computer simulation show deformation that is characteristic of tensile failure of spiralled cardboard tubes and hollow plant cells.

Author(s): R.-L. Ballouz [sup.1] , K. J. Walsh [sup.2] , O. S. Barnouin [sup.3] , D. N. DellaGiustina [sup.1] , M. Al Asad [sup.4] , E. R. Jawin [sup.5] , [...], An asteroid's history is determined in large part by its strength against collisions with other objects.sup.1,2 (impact strength). Laboratory experiments on centimetre-scale meteorites.sup.3 have been extrapolated and buttressed with numerical simulations to derive the impact strength at the asteroid scale.sup.4,5. In situ evidence of impacts on boulders on airless planetary bodies has come from Apollo lunar samples.sup.6 and images of the asteroid (25143) Itokawa.sup.7. It has not yet been possible, however, to assess directly the impact strength, and thus the absolute surface age, of the boulders that constitute the building blocks of a rubble-pile asteroid. Here we report an analysis of the size and depth of craters observed on boulders on the asteroid (101955) Bennu. We show that the impact strength of metre-sized boulders is 0.44 to 1.7 megapascals, which is low compared to that of solid terrestrial materials. We infer that Bennu's metre-sized boulders record its history of impact by millimetre- to centimetre-scale objects in near-Earth space. We conclude that this population of near-Earth impactors has a size frequency distribution similar to that of metre-scale bolides and originates from the asteroidal population. Our results indicate that Bennu has been dynamically decoupled from the main asteroid belt for 1.75 [plus or minus] 0.75 million years. Analysis of the size and depth of craters on boulders on the asteroid (101955) Bennu indicates that Bennu has been in near-Earth space for 1.75 [plus or minus] 0.75 million years.

Author(s): Ching-Yao Lai [sup.1] , Jonathan Kingslake [sup.1] [sup.2] , Martin G. Wearing [sup.3] , Po-Hsuan Cameron Chen [sup.4] , Pierre Gentine [sup.5] , Harold Li [sup.6] , Julian J. [...], Atmospheric warming threatens to accelerate the retreat of the Antarctic Ice Sheet by increasing surface melting and facilitating 'hydrofracturing'.sup.1-7, where meltwater flows into and enlarges fractures, potentially triggering ice-shelf collapse.sup.3-5,8-10. The collapse of ice shelves that buttress.sup.11-13 the ice sheet accelerates ice flow and sea-level rise.sup.14-16. However, we do not know if and how much of the buttressing regions of Antarctica's ice shelves are vulnerable to hydrofracture if inundated with water. Here we provide two lines of evidence suggesting that many buttressing regions are vulnerable. First, we trained a deep convolutional neural network (DCNN) to map the surface expressions of fractures in satellite imagery across all Antarctic ice shelves. Second, we developed a stability diagram of fractures based on linear elastic fracture mechanics to predict where basal and dry surface fractures form under current stress conditions. We find close agreement between the theoretical prediction and the DCNN-mapped fractures, despite limitations associated with detecting fractures in satellite imagery. Finally, we used linear elastic fracture mechanics theory to predict where surface fractures would become unstable if filled with water. Many regions regularly inundated with meltwater today are resilient to hydrofracture--stresses are low enough that all water-filled fractures are stable. Conversely, 60 [plus or minus] 10 per cent of ice shelves (by area) both buttress upstream ice and are vulnerable to hydrofracture if inundated with water. The DCNN map confirms the presence of fractures in these buttressing regions. Increased surface melting.sup.17 could trigger hydrofracturing if it leads to water inundating the widespread vulnerable regions we identify. These regions are where atmospheric warming may have the largest impact on ice-sheet mass balance. Using a neural network trained on continent-wide data and a fracture model, the ice shelves in Antarctica that may be prone to hydrofracturing under further atmospheric warming are identified.

Author(s): Jamie I. Farquharson [sup.1] , Falk Amelung [sup.1] Author Affiliations: (1) Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, USA Main Compelling evidence exists for seismicity [...], The May 2018 rift intrusion and eruption of Kilauea Volcano, Hawai'i, represented one of its most extraordinary eruptive sequences in at least 200 years, yet the trigger mechanism remains elusive.sup.1. The event was preceded by several months of anomalously high precipitation. It has been proposed that rainfall can modulate shallow volcanic activity.sup.2,3, but it remains unknown whether it can have impacts at the greater depths associated with magma transport. Here we show that immediately before and during the eruption, infiltration of rainfall into Kilauea Volcano's subsurface increased pore pressure at depths of 1 to 3 kilometres by 0.1 to 1 kilopascals, to its highest pressure in almost 50 years. We propose that weakening and mechanical failure of the edifice was driven by changes in pore pressure within the rift zone, prompting opportunistic dyke intrusion and ultimately facilitating the eruption. A precipitation-induced eruption trigger is consistent with the lack of precursory summit inflation, showing that this intrusion--unlike others--was not caused by the forceful intrusion of new magma into the rift zone. Moreover, statistical analysis of historic eruption occurrence suggests that rainfall patterns contribute substantially to the timing and frequency of Kilauea's eruptions and intrusions. Thus, volcanic activity can be modulated by extreme rainfall triggering edifice rock failure--a factor that should be considered when assessing volcanic hazards. Notably, the increasingly extreme weather patterns associated with ongoing anthropogenic climate change could increase the potential for rainfall-triggered volcanic phenomena worldwide. Immediately before and during the eruption of Ki[combining macron]lauea Volcano in May 2018, anomalously high rainfall increased the pore pressure in the subsurface to its highest level in 50 years, causing weakening and mechanical failure of the edifice.

Author(s): Jianwei Song [1]; Chaoji Chen [1]; Shuze Zhu [2]; Mingwei Zhu [1]; Jiaqi Dai [1]; Upamanyu Ray [2]; Yiju Li [1]; Yudi Kuang [1]; Yongfeng Li [1]; Nelson Quispe [...]

Along the neck of 67P's nucleus (the Hapi region) are two straight cracks, each a few hundred metres long and separated from each other by 750 metres (Fig. 1a, b) [...], The solid, central part of a comet--its nucleus--is subject to destructive processes (1,2), which cause nuclei to split at a rate of about 0.01 per year per comet (3). These destructive events are due to a range of possible thermophysical effects (4); however, the geophysical expressions of these effects are unknown. Separately, over two-thirds of comet nuclei that have been imaged at high resolution show bilobate shapes (5), including the nucleus of comet 67P/Churyumov-Gerasimenko (67P), visited by the Rosetta spacecraft. Analysis of the Rosetta observations suggests that 67P's components were brought together at low speed after their separate formation (6). Here, we study the structure and dynamics of 67P's nucleus. We find that sublimation torques have caused the nucleus to spin up in the past to form the large cracks observed on its neck. However, the chaotic evolution of its spin state has so far forestalled its splitting, although it should eventually reach a rapid enough spin rate to do so. Once this occurs, the separated components will be unable to escape each other; they will orbit each other for a time, ultimately undergoing a low-speed merger that will result in a new bilobate configuration. The components of four other imaged bilobate nuclei have volume ratios that are consistent with a similar reconfiguration cycle, pointing to such cycles as a fundamental process in the evolution of short-period comet nuclei. It has been shown (7,8) that comets were not strong contributors to the so-called late heavy bombardment about 4 billion years ago. The reconfiguration process suggested here would preferentially decimate comet nuclei during migration to the inner solar system, perhaps explaining this lack of a substantial cometary flux.

It has long been assumed that seismogenic faulting is confined to cool, brittle rocks, with a temperature upper limit of ~600°C (ref. 1). This thinking underpins our understanding of volcanic [...]

Author(s): Jonathan M. Ramsey [1, 2]; Frederick M. Chester (corresponding author) [1] Fracture is a fundamental mechanism of material failure. Two basic types of brittle fractures are commonly observed in [...]

Author(s): Hyoung-Joon Jin; David L. Kaplan (corresponding author) Silk spinning by insects and spiders leads to the formation of fibres that exhibit high strength and toughness [1]. The lack of [...]

Author(s): J. Y. Huang (corresponding author) [1]; S. Chen [1]; Z. Q. Wang [1]; K. Kempa [1]; Y. M. Wang [2]; S. H. Jo [1]; G. Chen [3]; M. S. [...]