  Giant impacts dominate the final stages of terrestrial planet formation and
set the configuration and compositions of the final system of planets. A giant
impact is believed to be responsible for the formation of Earth's Moon, but the
specific impact parameters are under debate. Because the canonical Moon-forming
impact is the most intensely studied scenario, it is often considered the
archetypal giant impact. However, a wide range of impacts with different
outcomes are possible. Here we examine the total energy budgets of giant
impacts that form Earth-mass bodies and find that they differ substantially
across the wide range of possible Moon-forming events. We show that
gravitational potential energy exchange is important, and we determine the
regime in which potential energy has a significant effect on the collision
outcome. Energy is deposited heterogeneously within the colliding planets,
increasing their internal energies, and portions of each body attain sufficient
entropy for vaporization. After gravitational re-equilibration, post-impact
bodies are strongly thermally stratified, with varying amounts of vaporized and
supercritical mantle. The canonical Moon-forming impact is a relatively low
energy event and should not be considered the archetype of accretionary giant
impacts that form Earth-mass planets. After a giant impact, bodies are
significantly inflated in size compared to condensed planets of the same mass,
and there are substantial differences in the magnitudes of their potential,
kinetic and internal energy components. As a result, the conditions for
metal-silicate equilibration and the subsequent evolution of the planet may
vary widely between different impact scenarios.
