Minimum Orbital Intersection Distance

The minimum orbital intersection distance (MOID) is the minimum distance between the osculating orbits of two objects. It indicates the closest possible approach of the two objects except where excluded by protective resonance.

As such, the MOID can act as an early warning indicator for collision between an asteroid and a planet. A large MOID between and asteroid and the Earth indicates the asteroid will not collide with Earth in the near term. Asteroids with a small MOID to Earth should be carefully followed because they can become Earth colliders.

Because of long-range planetary gravitational perturbations and, particularly, close planetary approaches, asteroid orbits change with time. Consequently, MOID also changes. As a rule of thumb, MOID can change by up to 0.02 AU per century, except for approaches within 1 AU of massive Jupiter, where the change can be large. Thus an asteroid that has a small MOID with any planet should be monitored.

Each day, we calculate the MOIDs between the inner solar system planets and near-Earth asteroids (NEAs). We limit the table of MOID values presented here to 0.05 AU or less for terrestrial planets and 1 AU or less for Jupiter.

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Last modified: 2008 April 29