We discuss the formation of a dusty accretion disk around an infant star and, from that, the planets. Telescopic observations of young stars suggest planet formation required only a few tens of millions of years, in agreement with a Solar System timescale based on measurements of radioactive isotopes in meteorites. The age of the Solar System, 4.567 billion years, is determined from calcium–aluminum inclusions (CAIs), the first-formed solids. Numerical simulations of planetary accretion further support this timescale and constrain the widths of feeding zones. The compositions of the terrestrial planets are broadly chondritic, but depletions in volatile elements suggest their assembly from already differentiated planetesimals. The ice giants have rocky cores that directly accreted nebular ices, and the even more massive gas giants have ice giant-like cores that swept up nebular gas. Leftover planetary building blocks – asteroids and comets – provide more detailed insights into planet formation processes. We complete this story by discussing the origin of the Moon by a giant impact, and the related topic of orbital perturbations possibly caused by migrations of the giant planets.

At its root, the word “astrobiology” means “biology of the stars.” It is the branch of science that concerns the origin and evolution of life on Earth – the only place that, at present, we are certain life exists – and the potential for life to be distributed across the Universe. In this chapter, we explore the evolutionary relationships of life on Earth and review the necessary ingredients and permissible environmental conditions for the origin and evolution of life. We also discuss the characteristics of early life on Earth, and the physical and geochemical evidence for life that might be used to target habitable environments – and potentially to detect evidence of life – elsewhere in the Universe.

All planets, and many moons and asteroids, have experienced igneous activity. Magma compositions on Earth vary widely, reflecting different melting mechanisms in the various tectonic settings, different source compositions, and the effects of magmatic processes like fractional crystallization and assimilation. Most magmas are emplaced in plutons rather than erupt on the surface. On other planets, we study volcanic constructs and rocks, because plutonic rocks are not commonly exposed. Eruptive styles vary with each planet, depending on neutral buoyancy zones in the subsurface, the amount of volatiles in magmas, gravity, atmospheric pressure, and other factors. Basalts are ubiquitous on all rocky bodies, and fractional crystallization of basaltic magmas has produced cumulates and fractionated residual melts. The formation of abundant, highly evolved felsic magmas, as far as we can presently discern, has been restricted to Earth. On some icy bodies cryovolcanoes erupt cold brines and gases. Volcanism mostly ceased on the Moon when melting retreated to the deep interior, on Mercury when global contraction closed pathways for magma ascent, and on asteroid Vesta when the radiogenic heat sources were exhausted. Magmatic activity continues on Earth and Io, and recent (possibly ongoing) activity occurs on Venus and Mars. Where sufficient information is available to judge, magma compositions appear to have evolved with time, in a manner unique to each body.

We describe the flow of liquids – water in the inner Solar System, hydrocarbons on Saturn’s moon Titan – and its effects on planetary surfaces. Liquids fall onto, flow through, and emerge from planetary landscapes. The resultant entrainment, transport, and deposition of sediment are observed in a variety of forms, which can be ascribed to the variety of surficial and subsurface flow conditions. As the area within the highest topographic elevations surrounding a river network, the drainage basin provides a natural hydrologic unit for defining and discussing these various processes. In cratered landscapes on Mars and Titan, drainage divides are often obscured by impact craters and by atmospheric degradation, although in younger terrains the crater rims themselves often demarcate the drainage divides. River networks exhibit morphologies based on surface and subsurface controls on the flow. Whereas networks on Earth are primarily dendritic (branching in a tree-like fashion), the majority of network morphologies on Titan are rectangular, suggesting tectonic influence. Deposits from channelized flow provide data on the flow conditions and sediment load. Fans on Mars and Titan provide evidence of subaerial deposition. Deltaic deposits on those bodies, along with possible shorelines and inferred tsunami deposits around the northern lowlands of Mars, imply deposition and erosion in lakes, seas, and perhaps even a vast martian ocean. Fluvial, alluvial, and lacustrine landforms thereby provide insights into climate, surface, and sedimentologic processes on planetary bodies.