This edge on view of the solar system from NASA's Wide-field Infrared Survey Explorer depicts the numbers of Near-Earth Asteroids and Potentially Hazardous Asteroids. The PHAs are depicted in bright orange, the NEAs in blue and the Earth's orbit in green. Image Credit/NASA
New estimates based on findings from NASA’s Wide-field Infrared Explorer, or WISE mission, reflect a big increase in the number of asteroids that could pose a collision threat to the Earth.
And experts suggest they have found only a third to a half of these potentially worrisome planetary objects.
Botton line: The new count says Earthlings are contending with roughly 4,700 potentially hazardous asteroids, or PHAs. WISE mission scientists suggest their latest estimate is likely off by plus or minus 1,500 PHAs.
PHAs are a subset of a class or planetary bodies known as near-Earth asteroids, or NEAs. Estimates of the numbers of NEAs also vary widely. PHA’s are objects that measure more than 330 feet across, large enough to survive a high velocity plunge into the Earth’s atmosphere to explode in the air or impact causing damage on a regional or wider scale.
Just two years ago, President Obama underscored the value of NEA’s when he directed NASA to develop the technologies to reach an NEA with astronauts by 2025. That mission should be a stepping stone to the future exploration of Mars by humans, the president said.
“NEOWISE analysis shows us we’ve made a good start at finding those objects that truly represent an impact hazard to Earth,”said Lindley Johnson, NASA mission executive for the spacecraft. “But we’ve many more to find, and it will take a concerted effort during the next couple of decades to find all of them that could do serious damage or be a mission destination in the future.”
A surprising number of the PHAs are bright, suggesting they are comprised on metals or granite, informative to scientists as they attempt to characterize how these objects would react as they dive into the Earth’s atmosphere.
The WISE telescope was launched in December 2009, equipped for a six month mission to catalogue dim and difficult to detect objects throughout the universe. As an adjunct, called NEOWISE, the telescope was assigned to hunt for NEAs.
The latest analysis of PHAs also suggests that twice as many as previously thought orbit the sun on a course closely alligned with the Earth’s trajectory.
That suggests they may have originated from a collision between two larger asteroids orbiting the sun between Mars and Jupiter. The breakup of a third asteroid may have disturbed some of the fragments causing them to drift into orbits that pass close to the Earth.
WISE surveyed the sky from its polar orbit twice before entering hibernation in early 2011. The telescope catalogued hundreds of millions of objects, from super bright galaxies, star forming regions of galaxies as well as closer to Earth asteroids.
The infrared sensors enabled WISE to measure the light, or heat coming from especially dim asteroids. That provided scientists with information that could be converted in size estimates