What does PHO mean in UNCLASSIFIED

Definition of PHO

PHO stands for Potentially Hazardous Object and refers to a celestial object that has been classified as having the potential to cause significant disruption or harm if it collided with Earth or another nearby astronomical body. The objects that are classified as PHOs must meet two criteria: they must be large enough and they must come within a certain distance of Earth's orbit (usually 7.5 million kilometres). By classifying these objects, astronomers can better assess their risk level and track them more closely for potential impacts.

Identification of PHO

In order to identify and classify an object as a PHO, astronomers use measurements such as the density, size, rotation rate and composition of the object from telescope images or from machines such as spectrometers. They also use calculations such as orbital elements (which describe its trajectory) or its Minimum Orbit Intersection Distance (MOID) – the shortest distance between its orbit and Earth's orbit – to determine whether it could pose a hazard if it came too close to our planet.

Potential Risk of PHO

Although all PHOs are considered potentially hazardous, not all pose an imminent threat. Astronomers assess each object based on its likelihood of colliding with Earth or another nearby planet over a certain period of time – usually 10 years or longer – before issuing any warnings about potential danger. While some asteroids have been identified which may pass within close proximity of Earth’s orbit in future years, none are expected to actually impact our planet any time soon.