Potentially

Hazardous Asteroids (PHAs).

Potentially Hazardous Asteroids (PHAs) are space objects that pose a potential threat to Earth due to their close approaches. They are defined by the criteria of the NASA Near Earth Object Observations Program for objects with an absolute magnitude (H) of 22.0 or less and which have an Earth Minimum Orbit Intersection Distance (MOID) of 0.05 astronomical units or less.

Definition

The term "Potentially Hazardous Asteroids" is specifically used for asteroids with an Earth Minimum Orbit Intersection Distance (MOID) of 0.05 astronomical units or less and an absolute magnitude (H) of 22.0 or less. This means that they have the potential to make threatening close approaches to the Earth. The absolute magnitude (H) of 22.0 or less is a measure of the asteroid's brightness, which indirectly indicates its size.

Detection and Tracking

The detection and tracking of PHAs is a major focus of the efforts of the NASA Near Earth Object Observations Program. This program uses both ground-based and space-based telescopes to search for, track, and characterize PHAs. The data collected is used to predict their future trajectories and determine if they pose a risk to Earth.

Risk Assessment

The risk posed by PHAs is assessed using a variety of methods. One of these is the Torino Scale, a tool for categorizing the impact hazard associated with near-Earth objects such as asteroids and comets. The scale ranges from 0 to 10, with 10 being a certain global catastrophe.

Mitigation

Several strategies have been proposed for mitigating the threat posed by PHAs. These include deflection strategies such as the use of a gravity tractor, kinetic impactor, or nuclear explosive device. Another proposed strategy is the use of a solar collector to heat the surface of the asteroid and create a propulsive thrust.

See Also

• Near-Earth object
• Asteroid impact prediction
• Asteroid deflection strategies
• Torino Scale