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