Results from NASA’s Wide-field Infrared Survey Explorer (WISE) have led to better data of our solar system’s population of potentially hazardous asteroids. These new results reveal data about their total numbers, origins and the possible dangers they may pose.
Potentially hazardous asteroids (abbreviated as PHAs) are part of the larger group of near-Earth asteroids. The PHAs have the closest orbits to Earth’s, coming within five million miles, and they are massive enough to land on Earth's surface and cause damage.
The new results come from the asteroid-hunting portion of the WISE mission, called NEOWISE. The project sampled 107 PHAs to make predictions about the entire population as a whole. Findings indicate there are roughly 4,700 PHAs, plus or minus 1,500, with diameters larger than 330 feet. So far, an estimated 20 to 30 percent of these objects have been found.
NASA's Wide Field Infrared Survey Explorer has sampled 107 'potentially hazardous asteroids' (PHAs) as shown in this diagram illustrating their orbits crossing Earth
While previous estimates of PHAs predicted similar numbers, they were rough approximations. NEOWISE has generated a better educated guess of the objects’ total numbers and sizes.
The new data also suggests that about twice as many PHAs as previously thought are likely to be in “lower-inclination” orbits, which are more aligned with the plane of Earth’s orbit. These lower-inclination objects appear to be brighter and smaller than the other near-Earth asteroids that spend more time far away from Earth. It is thought that many of these PHAs may have originated from a collision between two asteroids in the main belt lying between Mars and Jupiter. A larger body with a low-inclination orbit may have broken up in the main belt, causing some of the fragments to drift into orbits closer to Earth and eventually become PHAs.
Asteroids with lower-inclination orbits would be more likely to crash on Earth and would be easier to reach. The results therefore suggest more near-Earth objects might be available for future robotic or human missions to either study or try to divert their paths.
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