The asteroid belt is a unique source of information on some of the most important questions facing solar system science. These questions include the sizes, numbers, types and orbital distributions of the planetesimals that formed the planets, and the identification of those asteroids that are the sources of meteorites and near-Earth asteroids. Answering these questions requires an understanding of the dynamical evolution of the asteroid belt, but this evolution is governed by a complex interplay of mechanisms that include catastrophic disruption, orbital evolution driven by Yarkovsky radiation forces, and chaotic orbital evolution driven by gravitational forces. While the timescales of these loss mechanisms have been calculated using estimates of some critical parameters that include the thermal properties, strengths and mean densities of the asteroids, we argue here that the uncertainties in these parameters are so large that deconvolution of the structure of the asteroid belt must be guided primarily by observational constraints. We argue that observations of the inner asteroid belt indicate that the size-frequency distribution is not close to the equilibrium distribution postulated by Dohnanyi (1969). We also discuss the correlations observed between the sizes and the orbital elements of the asteroids. While some of these correlations are significant and informative, others are spurious and may arise from the limitations of the Hierarchical Clustering Method that is currently used to define family membership.

As staples of science fiction, space technologies, much like outer space itself, have often been regarded as being ‘out there’ objects of international security analysis. However, as a growing subset of security scholarship indicates, terrestrial politics and practices are ever more dependent on space technologies and systems. Existing scholarship in ‘astropolitics’ and ‘critical astropolitics’ has tended to concentrate on how such technologies and systems underpin and impact the dynamics of military security, but this article makes the case for wider consideration of ‘orbital infrastructures’ as crucial to conceptions and governance of planetary security in the context of the ‘Anthropocene’. It does so by outlining and analysing in detail Earth Observation (EO) and Near-Earth Object (NEO) detection systems as exemplary cases of technological infrastructures for ‘looking in’ on and ‘looking out’ for forms of planetary insecurity. Drawing on and extending recent theorisations of technopolitics and of Large Technical Systems, we argue that EO and NEO technologies illustrate, in distinct ways, the extent to which orbital infrastructures should be considered not only part of the fabric of contemporary international security but as particularly significant within and even emblematic of the technopolitics of planetary (in)security.

Close encounters of Near Earth Objects (NEOs) with large asteroids are a possible source of systematic errors in trajectory propagations and asteroid mitigation. It is, thus, necessary to identify those large asteroids that have to be considered as perturbers in NEO orbit modeling. Using the Standard Dynamical Model we searched for encounters between the 1649 numbered Near Earth Asteroids (NEAs) and 2191 large asteroids having sizes greater than 20 km. Investigating the 21st century A. D. we have found 791 close encounters with 195 different large asteroids that lead to a substantial scattering of NEOs.

The dynamical evolution of short-period objects having perihelia at small heliocentric distances is discussed. We have investigated the motion of multiple-apparition members of the Marsden and Kracht sungrazing groups. The orbital evolution of these objects on timescales < 10 Kyr is mainly determined by the Kozai-Lidov secular perturbations. These objects are dynamically connected with high-inclination near-Earth objects. On the other hand, we have found several observed near-Earth objects that evolve in the same way, reaching small perihelion distances on short timescales in the past.

The review contains the most recent data on near-Earth objects such as their sizes and densities, rotation and shapes, taxonomy and mineralogy, optical properties and structure of their surfaces, binary systems among the NEOs and internal structure of asteroids and comets constituted the NEO population.

The distribution of Near-Earth Objects, in particular Near-Earth asteroids is examined using maximum likelihood methods. These are analysed with respect magnitudes, taxonomic classes and to their orbital distances. Comparisons are made with the distributions of main-belt asteroids and short-period comets.

While the physical characterization of near-Earth objects (NEOs) is progressing at a much slower rate than that of discovery, a substantial body of thermal-infrared data has been gathered over the past few years. A wide variety of taxonomic classes in the NEO population have now been sampled by means of thermal-infrared spectrophotometric observations. The resulting albedo information, together with the distribution of taxonomic types from spectroscopic investigations and the rapidly increasing catalog of orbits and absolute magnitudes derived from NEO search programs, such as LINEAR, facilitates more accurate estimates of the size distribution of the NEO population and the magnitude of the impact hazard. Despite our rapidly increasing knowledge of the NEO population, many questions and uncertainties remain, such as: How does the albedo distribution of NEOs compare with that of main-belt asteroids, and does space weathering play a role? How does the surface structure and regolith coverage of NEOs vary with size and taxonomic type? What fraction of NEOs are extinct comets? A property of particular interest is the surface thermal inertia of small asteroids, which is an indicator of the presence or lack of a thermally-insulating surface layer. Large asteroids can accumulate regolith, but can very small asteroids retain thermally-insulating collisional debris or at least a dust layer? Knowledge of thermal inertia is important for accurate calculations of the Yarkovsky effect, which can significantly influence the orbital evolution of potentially hazardous NEOs, and for the design of instruments for lander missions. Contrary to earlier expectations, evidence appears to be accumulating that even sub-kilometer asteroids often have a significant thermally-insulating surface layer. Recent results from thermal-infrared investigations of NEOs are reviewed and implications for the surface properties of small asteroids discussed.