Within the general framework of differentiation in the early solar system, the asteroid Vesta is a particularly interesting case study. First, its size is well constrained, simplifying modeling efforts that can concentrate on bodies of relevant size. Second, the rich diversity of HED meteorites provides constraints on bulk composition and a unique opportunity to confront predictions of numerical models with petrologic reality. Finally, the Dawn mission, in addition to confirming the link between Vesta and the HED’s, also provides critical constraints on the internal density structure and composition of the asteroid. In this chapter we begin by considering petrologic and geochemical constraints on the bulk composition and differentiation time-scales of Vesta, before presenting modeling efforts to understand its chemical and physical evolution. The modeling indicates accretion within the first million years of solar system history and complex thermal and chemical retroactions linked to the redistribution of 26Al during transport of melt toward the surface. Formation of a shallow magma ocean is predicted, leading to a vertically stratified mineralogical structure with olivine sequestered at depth and protracted cooling at depth. These features are consistent with the essential features of HED petrology and chronology and observations of the Dawn mission.

From the viewpoint of planet formation in the Solar System, Main Belt asteroids are the remnants of the so-called planetesimal population, the building bricks of planets that formed ubiquitously all over the Solar Nebula. Over the last years evidence has grown that planetesimals formed big from the gravitational collapse of a local accumulation of mm–cm sized so-called pebbles, rather than small, as models of collisional coagulation would suggest. The precise size distribution of original planetesimals remains a central question in planetology. An asteroid (and other small bodies) could be a fragment of a larger parent body or it could be an original planetesimal. Here, we outline observational and theoretical constraints on the formation of MBAs. We discuss the current state of research on the size–frequency distribution, the ages of asteroids, and the implications on the formation of asteroids. We review planetesimal formation theory, specifically focusing on the initial sizes of primordial planetesimals.

Classification, physical properties, orbits, evolution of asteroids, comets, and KBOs

Isotope fractionations and their causes in extraterrestrial materials, nucleosynthetic isotope anomalies

Time constraints on the formation and early evolution of planetesimals and planets

Relationship between cosmochemistry and geochemistry, historical beginnings of cosmochemistry, tools of cosmochemistry

Geochemical measurements and constraints on the origin of the two best-studied bodies: the Moon and Mars

Compositions and classification of chondritic and differentiated meteories and of interplanetary dust particles

Cosmochemical constraints on models for the formation and early evolution of our solar system and exoplanets

Chemical compositions of asteroids, comets, and their samples

Condensation, evaporation, chemical and physical processes that partition elements

Condensation of ices, noble gas isotope components and organic matter in extraterrestrial materials

Types of presolar grains, how they are analyzed, and what their compositions reveal

How radioactive isotope systems are used to derive ages in extraterrestrial materials