NASA New Count - 4700 Potentially Hazardous Asteroids - Size larger than 100 meters

In NASA latest release Observations from NASA's Wide-field Infrared Survey Explorer (WISE) were presented which have led to the best assessment yet of our solar system's population of potentially hazardous asteroids. A total of 4700 Potentially Hazardous Asteroids (+ or - 1500) with Size larger than 100 meters have been estimated accurately.

What are Potentially Hazardous Asteroid ? 
Also known as "PHAs," these asteroids have orbits that come within five million miles (about eight million kilometers) of Earth, and they are big enough to survive passing through Earth's atmosphere and cause damage on a regional, or greater, scale.

What is the present number of Potentially Hazardous Asteroids as per new count? How many have been found ?
here are roughly 4,700 PHAs, plus or minus 1,500, with diameters larger than 330 feet (about 100 meters). So far, an estimated 20 to 30 percent of these objects have been found.

Did NASA WISE Mission count all the PHA present ? 
No, Using the Sample of 107 PHAS from  WISE Missions asteroid-hunting portion (called NEOWISE) made this scientific prediction about the population as a whole.

Why Asteroids are so Important to Note ? 

Why are talking about this now ?
In latest NASA Release dated 17th May 2012 Mailed to us at 7.a.m. (16th May US timings).

Scientists Observations from NASA's Wide-field Infrared Survey Explorer (WISE) have led to the best assessment yet of our solar system's population of potentially hazardous asteroids.

Can you give us the picture of PHA as would be seen from Space ? 
Yes here is the simulated view of the near-Earth asteroid population presented with various colours. In the picture Earth Orbit is Green.

PHA (scatter, 558px)
Orange Colour are PHA'S : potentially hazardous asteroids (PHAs) are denoted in orange. 
Less dangerous near-Earth asteroids are blue.
Does this Mean till this release was made Scientists didnt know how many PHA's are there ? 
No scientist had some estimates previously of PHAs with was in similar in numbers as it announced now. But previous estimates were rough approximations.

Whereas NEOWISE has generated a more credible estimate of the objects' total numbers and sizes.

How important is WISE Space Telescope Data ? 
WISE space telescope has counted both light and dark objects (not easy to detect with normal techniques) using  infrared light, or heat, of asteroids.

According to said Lindley Johnson, program executive for the Near-Earth Object Observation Program at NASA Headquarters."The NEOWISE analysis shows us we've made a good start at finding those objects that truly represent an impact hazard to Earth," .

"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."

PHA (orbits, 200px)
This orbit diagram illustrates the difference between a PHA and less hazardous near-Earth asteroids (NEA). 
What was newly found in the latest analysis of Scientists using WISE Mission ? 
The new analysis suggests that about twice as many PHAs as previously thought reside in low-inclination orbits, which are roughly aligned with the plane of Earth's orbit.

"Our team was surprised to find the overabundance of low-inclination PHAs," said Amy Mainzer, NEOWISE principal investigator, at NASA's Jet Propulsion Laboratory.

"Because they will tend to make more close approaches to Earth, these targets can provide the best opportunities for the next generation of human and robotic exploration."

What does th NEOWISE Suggest ? Collsion between Asteroids Suspected ?  
The NEOWISE analysis suggests a possible origin for the low-inclinaton PHAs: Many of them could 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.

The lower-inclination PHAs appear to be somewhat brighter and smaller than other near-Earth asteroids.

The discovery that PHAs tend to be bright says something about their composition; they are more likely to be either stony, like granite, or metallic. This type of information is important in assessing the space rocks' potential hazards to Earth. The composition of the bodies would affect how quickly they might burn up in our atmosphere if an encounter were to take place.

"The NEOWISE project, which wasn't originally planned as part of WISE, has turned out to be a huge bonus," said Mainzer.  "Everything we can learn about these objects helps us understand their origins and fate."


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