The Earth is the yardstick against which the state of isostasy on the terrestrial planets will be assessed in the future. The primary data sets will continue to be gravity anomaly and topography data together with seismic data which have the potential to image the surfaces of flexure directly. We are close to defining the relative contributions of plate flexure and mantle dynamics in contributing to Earth’s topography and gravity fields as well as to its crustal structure and vertical motion history. The acquisition of higher-resolution data will increase the number of estimates of Te of the planets which, in turn, will help us to understand better the complexities of their geodynamical evolution.

This chapter serves as an introduction to the book. It discusses the origin of Planet Earth and its Moon, their dependence on the Sun for energy, and the evolution of life on Earth. The evolution of the first living cell seems to have been a single event and all life on Earth is directly derived from this individual primary organism. The first life forms were anaerobic bacteria, but these later gave rise to photosynthesising cyanobacteria, which produced oxygen. The presence of oxygen eventually led to the emergence of aerobic animals and plants. The chapter then details the emergence of the oceans and supercontinents Pangea and Gondwanaland, the eventual break-up of the supercontinents and the development of the varied ecosystems which characterise Planet Earth at the present time.

At least 14 space agencies have identified ‘in situ resource utilization’ as a necessary capability for long-duration missions, including crewed missions to the Moon, Mars and deep space. Attention is focused on the potential production of rocket fuel from ice and water-bearing minerals. If fuel can be sourced in space, it will not need to be lifted, at great expense, from Earth’s surface. But while the mining of asteroids and other celestial bodies offers benefits, it will also create risks. Mining that is motivated purely by resource extraction could overlook or even destroy important scientific information, while physical interactions with an asteroid could alter its trajectory and, in some circumstances, potentially create a human-caused Earth impact risk. There are presently two competing efforts to develop widely agreed rules on space mining. The first is an industry-friendly effort in which the United States is engaging in bilateral negotiations with dozens of states, encouraging them to sign the non-binding Artemis Accords. The second is a multilateral effort that fully considers the interests of non-spacefaring states and is taking place in the United Nations Committee on the Peaceful Uses of Outer Space.

A first shock of the Paradiso is to discover that it has difference, diversity and degrees. Dante questions Piccarda, the lovely sister of his childhood pal, as to whether she doesn’t yearn to have a more exalted station and to be friends with people in higher places. Her response is that the virtue of charity quiets their will so that they do not want anything other than what they have. Since Piccarda was taken against her will by her powerful brother’s henchmen from the convent where she had wanted to sleep and wake with Christ her whole life, and forced into a marriage she did not want, her acquiescence to the will of others seems to endure even in heaven. Yet appeasement in the face of violent threats turns out to be the opposite of resting in the truth of one’s own particular capacity for goodness, in a spectrum of possible goodness that soars way over our heads.

Stoppard’s one novel, Lord Malquist and Mr Moon, is an often-overlooked work which explores the actuality of a historical crisis in national identity. The novel is an imaginative appropriation of contemporary attitudes and tropes. It deserves attention as the work of a writer whose cultural and political antennae are as finely tuned as his literary sensibility.

Empedocles (about 492–430 BCE) promoted himself as a daimon in flesh. He told a cosmic story about how daimones fell from their blessed state and the mode of their return. The pure daimon is a spherical being made up of the energy of Love. Owing to a moral fault, the individual daimon falls into flesh and enters a drawn-out cycle of moral and physical purification. The fallen daimon purifies itself by living the lives of different animals and plants and by not eating substances that contain the daimonic essence. Empedocles is historically significant for his focus on individual and present daimonification, and for his cosmic story of daimonic fall and redemption, a story moralized by Plato and his intellectual heirs.

Here, I describe the Earth’s biosphere, which is not a sphere at all but rather a spherical shell. I discuss how far it extends in both directions. The question of how deep the biosphere goes takes us underground and to the bottoms of deep ocean trenches. The question of how far up it extends takes us to the stratosphere and the ozone layer that it contains. Next, I deal with plate tectonics. The recycling of the mobile plates that form the base of the biosphere has many consequences, including the obliteration of impact craters, in contrast to their near-permanence on the Moon. I then consider the extent to which the biosphere can be divided up into areas in which the predominant life-forms are different from each other. The marine component covers about 70% of Earth’s surface and is sometimes referred to as the global ocean, to emphasize its lack of real boundaries. Although the land component is smaller (about 30% of Earth’s surface), this component can be divided into biogeographic realms in which evolution has operated quasi-independently. Finally, I look back at the biosphere’s history, including such phenomena as glaciations, supercontinents, and the Great Oxygenation Event that occurred some 2.5 billion years ago.

Advanced spectroscopic sensors recently flown to the Moon have revealed unexpected discoveries about Earth’s nearest neighbor as well as provided detailed insights and constraints about how early crust evolves on an airless planetary body. Discussed here are (a) global assessment of the variety and distribution of major lunar mineral components and lithologies; (b) some of the remarkable new findings, such as the pervasive presence of OH across the surface and new rock types identified (Mg-spinel anorthosite) that are not identified in current lunar samples; and (c) expectations for the future as additional modern sensors provide a stronger foundation for remote compositional analysis of the Moon. Spectroscopic data continue to provide the cornerstone for identifying and understanding the regional and global character of lunar compositional variations and document key products and processes of crustal evolution.

Spectral modeling techniques have been developed for the analysis of planetary surfaces using large thermal infrared (TIR) spacecraft datasets. These techniques can be applied to three main spectral analysis problems: (1) correction for atmospheric effects for the recovery of surface emissivity; (2) isolation and separation of surface spectral endmembers for the characterization of surface mineralogy; and (3) determination of surface anisothermality for the retrieval of surface physical properties and correction for thermal emission in near-infrared spectral data. These modeling techniques have been extensively applied to martian and lunar spacecraft datasets, forming a basis for the retrieval of surface physical and compositional properties.

This chapter provides a brief review of missions using X-ray, gamma-ray, and neutron spectroscopy to determine the chemical composition of planetary surfaces. This chapter presents the history of planetary radiation measurements, including significant discoveries. Summary tables with links to the archived data provide a resource for readers interested in working in this field. Upcoming missions and possible future directions are described.

An ever-increasing number of laboratory facilities are enabling in situ spectral reflectance measurements of materials under conditions relevant to all the bodies in the Solar System, from Mercury to Pluto and beyond. Results derived from these facilities demonstrate that exposure of different materials to various planetary surface conditions can provide insights into the endogenic and exogenic processes that operate to modify their surface spectra, and their relative importance. Temperature, surface atmospheric pressure, atmospheric composition, radiation environment, and exposure to the space environment have all been shown to measurably affect reflectance and emittance spectra of a wide range of materials. Planetary surfaces are dynamic environments, and as our ability to reproduce a wider range of planetary surface conditions improves, so will our ability to better determine the surface composition of these bodies, and by extension, their geologic history.

Radar has proven to be a powerful tool in planetary exploration. Most of the major solid bodies of the Solar System have been observed with radar, either from Earth or from spacecraft. Planetary radar studies are reviewed in this chapter, with information on the various techniques of radar remote sensing provided along with key results. Recent radar results are emphasized. Concluding remarks are provided on future directions in planetary radar remote sensing.

Space missions have shown that most terrestrial bodies have an internally generated magnetic field in their metallic core and/or a crustal field due to remanent magnetism. The latter indicates the presence of an old dynamo at the time of crust formation. Information on the two together helps to uncover the body’s magnetic field history, and it is generally accepted that convection flows driven by thermal or compositional buoyancy in the cores are the most likely source for maintaining global planetary magnetic fields. The convection flow in the core, in turn, is closely related to the interior dynamics of the mantles above and the thermal evolution of the body. This chapter describes the mechanisms for dynamo generation either by thermal or compositional convection in the core. It discusses the magnetic field evolution of Mercury, Moon, Mars, Ganymede, and planetesimals and will also address the possibility of dynamo generation in rocky exoplanets