Questions regarding objects whose orbits bring them in close proximity to Earth, posing potential hazard.
A near-Earth object is any small or medium sized celestial body[mostly asteroids, but some are comets] whose orbit around the sun brings it into close proximity with Earth. However, other definition exist. Another one is that a celestial object whose perihelion is less than 1.3 AU is considered a near-Earth Object. Some near-Earth Objects have elliptical orbits that cross with the Earth's orbit. If such an object is larger than 140 meters across, it is then considered a potentially hazardous object.