Scientists are using an asteroid's close encounter with the Earth to test the planet's defense systems.  NASA says the space rock will come within 26,000 miles of the planet overnight.  That's far enough that it won't be a threat, but close enough for NASA to conduct a drill to see how well its planetary defense systems would work if a real asteroid was heading our way.  NASA doesn't expect to have to put the plan in effect for a while.  

They say no known asteroid poses a threat to the planet over the next 100 years, but you can never be too prepared.

Photo: AOL