NASA says monster asteroid no longer a threat

NASA said Friday that an asteroid 1,100 feet (340 meters) across poses no risk of hitting the Earth, according to new radar observations made earlier in March.

Discovered in 2004, "Apophis" had been thought of as one of the most "hazardous asteroids that could impact Earth," NASA said. 

But astronomers changed that impact assessment after getting a more refined estimate of Apophis' orbit around the sun. 

How big was the risk?

"When I started working with asteroids after college, Apophis was the poster child for hazardous asteroids," said Davide Farnocchia of NASA's Center for Near-Earth Object Studies. 

"There's a certain sense of satisfaction to see it removed from the risk list," he added. 

Apophis originally had been considered an impact risk during a flyby past Earth predicted for 2029. However, that risk was later ruled out, along with another potential impact risk in 2036.

There was another chance for impact in 2068. However, "powerful radar observations" made on March 5 allowed for the orbit estimate to be recalculated more precisely.  

"A 2068 impact is not in the realm of possibility anymore, and our calculations don't show any impact risk for at least the next 100 years," said Farnocchia.

How did NASA track the asteroid?

NASA astronomers used a 70-meter (230-foot) radio antenna stationed in California to track Apophis more closely. 

This removed the range of uncertainty for its orbit from "hundreds of kilometers, to just a handful of kilometers," said Farnocchia. 

"This greatly improved knowledge of its position in 2029 provides more certainty of its future motion, so we can now remove Apophis from the risk list," he added.

NASA scientist Marina Brozovic said that the radar imagery of the asteroid taken from 17 million kilometers away allowed for images of "remarkable resolution." 

"If we had binoculars as powerful as this radar, we would be able to sit in Los Angeles and read a dinner menu at a restaurant in New York," she said.