The Hill sphere is the neighborhood of a smaller body in which its gravity can dominate tidal perturbations from a larger primary.
A scale for the combined gravitational influence of two small orbiting bodies relative to their common host star. It is often used to express the separation of neighboring planetary embryos. For equal masses and nearly equal orbital radii it exceeds the individual Hill radius by .
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The Hill sphere, named after the American mathematician George William Hill, is a region around a celestial body where it exerts a dominant gravitational influence over other objects. Within this sphere, the body's gravity is strong enough to capture or retain smaller objects, such as moons, satellites, and debris, while outside this region, the gravitational influence of a more massive body (like a planet or a star) may take precedence.