The space rock, called 2004 BO41, is estimated at anywhere from 700 metres to a mile in length. The celestial body, which has been observed since its discovery in 2004, will pass at a relatively comfortable 7.3 million miles, which is still considered a "near Earth pass" by NASA due to the size of the cosmos. But, whereas, the US space agency is almost certain of the objects orbit, a much smaller asteroid, which is coming in much closer, and on an uncertain flight path, a few days later is being monitored much more closely. This large asteroid was discovered just a week ago and could devastate a city if it struck earth. NASA says it is heading towards Earth on "a highly uncertain orbit". The space rock is being closely monitored by space agencies across the globe, as it is due to whistle past within just days. The space rock, which is estimated to be up to 61 metres in length, is predicted to whistle past our planet at 31,000 miles per hour, on September 17, but NASA is not even