potentially hazardous object

A potentially hazardous object (PHO) is a near-Earth asteroid or comet with an orbit such that it has the potential to make close approaches to the Earth and is of a size large enough to cause significant regional damage in the event of impact. A potentially hazardous object with a reasonably well determined orbit can be known not to be a threat to Earth for the next 100 years or more. Potentially hazardous asteroids with a threat of impacting Earth in the next 100 years are listed on the Sentry Risk Table.