MOID (Minimum Orbital Interseccion Distance) The MOID indicates the closest possible approach of two objects, and it is the minimum distance between the osculating orbits of the two objects. A large MOID between the Earth and an asteroid indicates that the asteroid will not collide with the Earth in the near future. On the other hand, asteroids with a small MOID could collide with the Earth and should be carefully tracked.

MT – megaton The energy freed during an impact is usually measured by Megatons (MT). 1 MT is the energy of almost 100 Hiroshima bombs. To have an idea of the scale of energies: if a 2 meters compact body with a speed of 20 Km/s impacts the Earth, about 1 MT is released.

Perihelion/Aphelion The orbit of any light object (such as an asteroid, a comet or a planet) orbiting around the Sun has the shape of an ellipse (described by the three Keplero's laws). In this orbit, two important geometrical points can be found, the perihelion, the point where the object is nearest to the Sun, and the aphelion, the point of this orbit where the object is farthest.

PHO A PHO is a Potentially Hazardous Object, an asteroid or comet with a MOID (Minimum Orbit Intersection Distance) of 0.05 AU or less and a diameter of ~ 150 m or more.  
 
Last update: 30 March 2006