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The minimum orbit intersection distance (MOID) is the minimum distance between the paths of two bodies that are orbiting the same body. It is simplified by ignoring perturbations, both between the two bodies and from other bodies close enough to affect them, i.e., treating their orbits as simple orbits around the central body (termed osculating orbits). As such, a small MOID suggests a chance of a future impact, and qualitatively, the smaller, the greater chance, and its simplification makes it a relatively-straightforward factor to calculate. It is of interest in evaluating possible future impacts between Earth and near-Earth object, but is also of more theoretical interest regarding the evaluation of possible histories of orbits: too much chance of an impact suggests an orbit could not have been the same in the distant past.