An asteroid that is capable of wiping out life across the globe is hurtling towards a close encounter with the planet.
The giant rock, named Asteroid 1998 QE2, will make its closest approach to Earth later tonight.
Although it will keep a safe distance of 3.6 million miles - roughly 15 times the distance between Earth and the Moon - the 1.7-mile long object is of great interest to astronomers.
Using powerful telescopes, they should be able to glimpse the asteroid's very own moon and observe some of the space rock's surface features.
Martin Archer, a space plasma physicist, warned that if the asteroid were to strike, "it would certainly have implications for life on Earth on a global scale".
"It would flatten everything within 200 miles and cause damage within 1,000 miles but a lot of dust would be released into the atmosphere, blocking the Sun," he said.
"It could certainly cause extinction for certain species.
"However, this is by no means the closest near-Earth object we've seen. We had one a couple of months ago that was well within our geostationary satellites.
"We certainly don't have to worry about this one at all."
Radar astronomer Lance Benner, who is based at Nasa's Jet Propulsion Laboratory in California, said scientists expect to obtain a series of high-resolution images of the asteroid as it skims past Earth.
He said: "Whenever an asteroid approaches this closely, it provides an important scientific opportunity to study it in detail to understand its size, shape, rotation, surface features, and what they can tell us about its origin.
"We will also use new radar measurements of the asteroid's distance and velocity to improve our calculation of its orbit and compute its motion farther into the future than we could otherwise."
Mr Archer said scientists are yet to discover every object that could one day pose a risk to life on Earth.
However, Alan Fitzsimmons, of the Astrophysics Research Centre at Queen's University Belfast, told Sky News that asteroid strikes are rare.
"Luckily objects of this size or larger only hit us about once every four million years," he said.
"Radar observations of 1998 QE2 will let us check it's not coming near us for a long time to come."