An asteroid is set to pass so close to Earth on Monday night that it will be visible with binoculars.
The 900m-long rock, named 2004 BL86, will come to within 1.2 million kilometres of Earth - about three times further away than the moon.
It is believed to be the closest the asteroid will come to Earth for the next 200 years.
NASA plans to take "detailed images" of the object which it is hoped will shed some light on its make-up.
Don Yeomans, of Nasa's Near-Earth Object Program, told the Independent: "While it poses no threat to Earth for the foreseeable future, it's a relatively close approach by a relatively large asteroid, so it provides us a unique opportunity to observe and learn more."
Nasa radar astronomer Lance Benner added: "At present, we know almost nothing about the asteroid, so there are bound to be surprises."
