AMORs have perihelions (closest approach to the Sun) of between 1 and
1.3 astronomical units (AU). AMORs approach within 0.3 AU of the Earth
but do not cross the Earth's orbit.
APOLLOs cross the Earth's orbit and have semi-major axes larger than 1 AU.
ATENs have semi-major axes less than 1 AU. All known ATENS cross the Earth's orbit.
OTHER UNUSUAL OBJECTS are neither NEAs nor Main-Belt Asteroids but have unusual eccentricities or inclinations.
POTENTIALLY DANGEROUS MINOR PLANETS are asteroids larger than 110 m whose orbits approach close to the Earth.