There has been a prodigious level of interest in graphene over recent decades, and also in (the closely related) carbon nanotubes (CNTs). This has included quite a strong focus on their mechanical properties, with various claims in particular being made about high strength levels, which relate to their extremely fine scale. Since the scope for their usage in isolation is relatively limited, at least in terms of exploitation of high strength levels, a lot of attention has been directed towards the production and use of composite materials containing them as reinforcement. Unfortunately, most of the hopes originally expressed have not been fulfilled. In fact, the mechanical properties of such composites have in all cases been inferior to those of conventional carbon fibre composites. This is partly due to severe difficulties in manufacturing composites with relatively high levels of well-dispersed, well-aligned reinforcement. However, this is not the only problem, since many of the original expectations were based on incomplete understanding of the issues involved in defining the strength of a material, with particular reference to the role of toughness. These CNT-reinforced composites tend to have a low toughness, as a direct consequence of their very fine scale. In this chapter, the issue of scale-related effects is first addressed in general terms, followed by information about some specifics of using fine-scale reinforcement (particularly CNTs).

The behaviour of composite materials is often sensitive to changes in temperature. This arises for two main reasons. First, the response of the matrix to an applied load is often temperature-dependent; and second, changes in temperature can cause internal stresses to be set up as a result of differential thermal contraction and expansion of the two constituents. These stresses affect the thermal expansivity (expansion coefficient) of the composite. Furthermore, significant stresses are normally present in the material at ambient temperatures, since it has in most cases been cooled at the end of the fabrication process. Changes in internal stress state on altering the temperature can be substantial and may influence the response of the material to an applied load. Thermal cycling can thus have strong effects on, for example, creep characteristics. Finally, the thermal conductivity of composite materials is of interest, since many applications and processing procedures involve heat flow of some type. This property can be predicted from the conductivities of the constituents, although the situation may be complicated by poor thermal contact across the interfaces.

We describe the near-surface wind profile, its relation to environmental conditions, and how it can be quantified. The freestream wind speed can be converted to a friction wind speed, which relates to the flow at the atmosphere–surface interface and thus to the entrainment of sediment. The minimum wind speed for entrainment of aeolian sediment depends on gravity and grain size, so that threshold wind speed differs for varying planetary conditions. The difference in transport mechanism for grains leads to different depositional morphologies, which provide clues to the wind speed, wind direction, and sediment availability. Erosional landforms likewise provide information on near-surface atmospheric processes and surface sediments, as well as bedrock lithologies. The study of aeolian landforms thus informs our understanding of the atmosphere, surface geology, and sedimentology on other planets.

The surfaces of terrestrial planets and icy satellites have enjoyed deformation marked by faults and folds. We use these geologic structures not only to characterize the morphology of the surfaces, but also to describe the motions, stresses, and deformation processes that created the structures. Ultimately, we can sum these structural data and interpretations to infer the tectonic deformation for large portions of, or even entire, planets and satellites. As we will see, understanding deformation at this large tectonic scale enables us to investigate what is driving overall planet or satellite development. We will also learn that while the expected will happen, conundrums exist too. For example, the rocks of terrestrial planets deform quite differently from the icy shells of the satellites of the gas giants, yet the magnitude of these differences and their causes can surprise us. On the other hand, Venus and Earth are quite similar in many planetary characteristics but have strikingly different tectonic histories, which challenges us to understand why.

The elastic behaviour of long and short fibre composites is described in Chapters 4–6. This involves considering the stresses in individual plies of a laminate (under an external load) and stress distributions within and around short fibres. This information is now used to explore how a composite material suffers microstructural damage, potentially leading to ultimate failure of some sort. There are two distinct aspects to these (highly important) characteristics. First, there is the onset and development of microstructural damage (mainly cracking of various types) as a function of applied load. Second, there are the processes that cause absorption of energy within a composite material as it undergoes such failure and fracture. The latter determine the toughness of the material and are treated on a fracture mechanics basis in Chapter 9. In the present chapter, attention is concentrated on predicting how applied stresses create stress distributions within the composite and how these lead to damage and failure. The treatment is largely oriented towards long fibre composites (particularly laminates), and also towards polymer-based composites, although most of the principles apply equally to discontinuous reinforcement and other types of matrix.

Heavily cratered surfaces emphasize the important geologic role of impacts on almost all planetary bodies. Large impacts (referred to as “hypervelocity” to indicate velocities of tens of kilometers per second) produce micro-, meso-, and macroscale deformations that can influence the structures of planetary crusts. Crater morphologies are described as simple, complex, and multi-ring, and correlate with crater size and inversely with gravity of the target body. Crater formation is envisioned in three stages: contact/compression, excavation, and modification, each characterized by different processes and geologic features. Shock metamorphism has affected all Solar System bodies, producing breccias containing planar deformation features, high-pressure polymorphs, and melts. Craters provide the basis for planetary stratigraphy and chronology. Massive impacts on the Earth have potential consequences for damaging the planetary ecosystem and biosphere.

With our preliminary survey of planetary bodies in the Solar System complete, we next turn our attention to developing an understanding of the tools that are used by planetary geologists to study these bodies. In this chapter, we will learn about some of the remote sensing techniques that are most commonly used in planetary geologic exploration. We will focus greatest attention on methods that employ light as the carrier of information about the remote target, but we will also consider some methods that employ the detection of other types of carriers. We will describe techniques that can be used from aircraft flying above the Earth, from spacecraft orbiting planets, and from landed and roving platforms on other worlds. We will examine both active and passive remote sensing techniques, provide guidance on how to select the right type of remote sensing method for the desired scientific outcome, and discuss the role of a successful ground campaign in the analysis of remote-sensing data when that option is available.

We explain how heat is produced by radioactive decay, segregation and exothermic crystallization of metallic cores, impacts, and tidal forces. Planetesimals in the early Solar System were most affected by the decay of short-lived radionuclides. Larger, rocky planets were heated primarily by large impacts and core segregation. Because rocks are poor conductors, heat retention in rocky bodies is a function of planet size. Large-scale melting to produce magma oceans was likely a common process facilitating differentiation to form cores, mantles, and crusts. Metallic liquids are probably necessary for core segregation. Primary crusts, formed during planetary differentiation, are rarely preserved. Mantles are residues from the extraction of silicate crustal melts and core materials. Differentiation of the giant planets was driven by density variations in high-pressure forms of gases, ices, and rock more than by heating and melting. The importance of the various planetary heat sources changes over time; in modern planets the effective heat sources are decay of long-lived radioisotopes and, for the Earth, exothermal crystallization of the liquid outer core.