When the 262-foot-wide asteroid will be about 604,500 miles away when it makes its closest approach to Earth Saturday afternoon said Don Yeomans, a planetary scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
"It's a pretty good size, but it's not getting that close, at least by recent standards," Yeomans told CNN.
The asteroid was only discovered Sunday because objects of that size can't be detected by search telescopes until they get fairly close, he said.
At it closest approach the asteroid, dubbed 2013ET, will be at about 2-1/2 times the distance from Earth to the moon.
Now that it is close enough to be seen even with amateur telescopes, astronomers have accurately charted its orbit to confirm it will only make a fly-by of our planet.