A Potentially Hazardous Asteroid (PHA) is a Near-Earth asteroid with an orbit and size that has a potential to make threatening close approaches to the Earth. An asteroid is considered a PHA if its Earth MOID (Minimum Orbit Intersection Distance) is less than 0.05 AU and its absolute magnitude is brighter than 22.0. By this definition, PHAs are usually bigger than about 150m in diameter, which is big enough to cause at least a region-wide catastrophe if it were to hit the Earth. By the summer of 2005NASA has listed just over 700 PHAs. Near-Earth asteroids (NEAs) are asteroids whose orbit intersects Earths orbit and which may therefore pose a collision danger, as well as being most easily accessible for spacecraft from Earth. ... The astronomical unit (AU or au or a. ... 2005 is a common year starting on Saturday of the Gregorian calendar and is the current year. ... The National Aeronautics and Space Administration (NASA), which was established in 1958, is the agency responsible for the public space program of the United States of America. ...
A PotentiallyHazardousAsteroid (PHA) is a Near-Earth asteroid with a size and an orbit such that it has a potential to make threatening close approaches to the Earth.
Once found, each PHA is being studied by various means, including optical, infrared and radar observations, to further determine its characteristics, such as size, composition, rotation state, and more accurately determine its orbit.
During asteroid close approaches to planets or moons, it will be subject to gravitational perturbation, modifying the orbit, and some times, a previously non-threatening asteroid may become a PHA or vice versa.
Gleason, A. Discovery of PotentiallyHazardousAsteroid 2002 AZ In MPEC 2002-A31.
Gleason, A. Followup Observations of Asteroids 2003 QB and 2003 SV In Gleason, A. Followup Observations of Asteroid 1998 FR In Gleason, A. Followup Observations of Periodic Comet P/2001 RG In Gleason, A. Followup of Asteroid 2003 WQ In Gleason, A. Followup Observations of Periodic Comet P/2003 UY In Gleason, A. and M. Block.
Follow-up observations of Asteroids 2001 FB, and 2003 SN In Gleason, A. Larsen.
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