Synestia is a theoretical astronomical structure that arises during the late stages of planet formation. It is formed when two planetary bodies collide with enough energy to vaporize and partially melt them, resulting in a rotating, donut-shaped mass of vaporized rock and metal. The concept was introduced in the early 21st century by scientists Sarah Stewart and Simon J. Lock, offering new insights into how planets, particularly Earth-like ones, might evolve following massive impacts. The unique characteristics of a synestia, including its toroidal shape and atmospheric properties, provide a compelling framework for understanding the formation and differentiation of terrestrial planets and moons.