150-foot asteroid will buzz Earth, no need to duck

One of the more immediate steps, planned for 2016, is the launch of a spacecraft to fly to a much bigger asteroid, collect samples and return them to Earth in 2023.

As for Asteroid 2012 DA14 — discovered last year by astronomers in Spain — scientists suspect it's made of silicate rock, but aren't sure. Its shape and precise size also are mysteries.

What they do know with certainty:

"This object's orbit is so well known that there's no chance of a collision," Yeomans repeated during Thursday's news conference.

Its close approach, in fact, will alter its orbit around the sun in such a way as to keep it out of Earth's neighborhood, at least in the foreseeable future, Yeomans said.

Johnson anticipates no "sky is falling thing" related to next week's flyby.

He and other scientists urged journalists to keep the close encounter in perspective.

"Space rocks hit the Earth's atmosphere on a daily basis. Basketball-size objects come in daily. Volkswagen-size objects come in every couple of weeks," Yeomans said.

The grand total of stuff hitting the atmosphere every day? "About 100 tons," according to Yeoman, though most of it arrives harmlessly as sand-sized particles.

Online:

NASA: http://www.nasa.gov/topics/solarsystem/features/asteroidflyby.html

University of Arizona: http://osiris-rex.lpl.arizona.edu/