Potentially Hazardous Asteroids

PHA / PHO

PHA refers to Potentially Hazardous Asteroids. The more correct term is Potentially Hazardous Object (PHO). A PHO is 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. An object is considered a PHO if its minimum orbit intersection distance (MOID) with respect to Earth is less than 0.05 AU (7,500,000 km) and its diameter is at least 100 to 150 meters. This is big enough to cause regional devastation to human settlements unprecedented in human history in the case of a land impact, or a major tsunami in the case of an ocean impact. Such impact events occur on average around once per 10,000 years.

Why PHAs were in news in 2012?

In a new study, scientists have identified the countries that are most likely to be worst hit by the catastrophic damage caused by asteroids. NASA’s Wide Field Infrared Survey Explorer has sampled 107 "potentially hazardous" asteroids near Earth – 330ft wide or larger – to make estimates about how many are out there – and the figure is a terrifying 47,000. The WISE survey now estimates there are 47,000 "potentially hazardous" asteroids. The new results come from the asteroid-hunting portion of the WISE mission, called NEOWISE . As per the survey, the top ten countries most at risk are: China, Indonesia, India, Japan, US, Philippines, Italy, UK, Brazil and Nigeria.