An asteroid a third of a mile wide is heading towards earth this week – but don't worry we won't need Bruce Willis to save us.
The rock, catchily named 2004 BL86, will just miss earth passing by at about three times the distance of the moon.
Although easily far enough away to be safe, the fly-by counts as a narrow encounter in astronomical terms.
On Monday January 26, it will fly past about 745,000 miles from Earth making it the nearest pass-by of Earth by any asteroid until 2027.
The fly-past next week should be close enough to be spotted by amateur astronomers with small telescopes or strong binoculars.
Dr Don Yeomans, retiring head of the US space agency Nasa's Near-Earth Object Programme office at the jet propulsion laboratory in Pasadena, California, said: "Monday January 26 will be the closest asteroid 2004 BL86 will get to Earth for at least the next 200 years.
"And 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."
The asteroid was found on January 30, 2004, by astronomers at the Lincoln Near-Earth Asteroid Research telescope in the US.
As the rock flies past, it will be watched by Nasa's Deep Space Network antennae in California, and the Arecibo Observatory in Puerto Rico.
"When we get our radar data back the day after the flyby, we will have the first detailed images," Lance Banner, who is leading the Goldstone radar observations, said. "At present, we know almost nothing about the asteroid, so there are bound to be surprises."
Nasa detects, tracks and characterises asteroids and comets using both ground- and space-based telescopes.
The Near-Earth Object Programme, also known as Spaceguard, searches for objects that might potentially pose a hazard to the Earth.
