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In terms of outer space, it's a very close call.

In Earth terms, when an asteroid passes by on Tuesday, it will be 324,600 kilometres away. Not close enough to worry about.

But NASA scientists are excited about the proximity of a space rock because they've been waiting 35 years for one this big to come this close to Earth again.

Known as 2005 YU55, the 400-metre wide asteroid is being tracked by ground antennas as it approaches from the direction of the sun. It's expected to come closest to Earth at 6:28 p.m. Eastern Time on Tuesday, as it makes its first return visit to our corner of the galaxy in 200 years.

But scientists say there is nothing to fear.

"We're extremely confident, 100 per cent confident, that this is not a threat," said NASA's Near Earth Object Program manager Don Yeomans. "But it is an opportunity."

In fact, when 2005 YU55 passes by on Tuesday evening, it will be closer to the moon -- at a distance of 241,000 km -- than Earth.

Scientists have been tracking this asteroid since 2005, hence the name, and hope to determine its makeup, including ice or water, when it gets close.

Read more: http://www.ctv.ca/CTVNews/SciTech/20...#ixzz1cxb3hLrm