The biggest ever asteroid that threatens a collision with Earth is due to skim past us in four days time on May 14th, 2015.
Astronomers are worried that the asteroid named 1999 FN53 could possibly collide with the Earth, which would be catastrophic in its impact, causing earthquakes, tsunamis and probable mass extinction.
Even though astronomers have calculated it will not collide with the Earth, the slightest deviation in its course could lead to devastation due to its close proximity.
The monster is more than TEN TIMES bigger than other meteorites currently visible on NASA’s Near Earth Object radar.
It is also double the size of the gargantuan 2014-YB35 which had astronomers around the world watching the skies in March.
Experts warn a collision would trigger an explosion similar to millions of megatons of TNT and would be capable of killing 1.5 billion people.
It would be far more destructive than the 1908 Tunguska Event which saw a 50-metre lump of extraterrestrial rock crash into Siberia.
It flattened around 80 million trees and sent a shock wave across Russia measuring five on the Richter scale.
The event is held by scientists as a benchmark for the catastrophic consequence of an asteroid impact with earth.
The gigantic lump of rock is travelling faster than 30,000 mph and will brush terrifyingly close to Earth on Thursday.
Bill Napier, professor of astronomy at the University of Buckinghamshire, said an impact would leave unimaginable destruction.
He said: “People are concerned about an impact from a very large asteroid, and the impact of something of this scale would be nothing short of global.
“It is certainly one of the biggest on the radar, and much bigger than the Tunguska asteroid which was one of the most significant in history.
“This is in a completely different ball park, we are talking about millions of megatons of energy, vastly more than was released in Hiroshima.
“It would undoubtedly lead to the deaths of around 1.5 billion people, we are looking at a mass extinction of humanity.
“To understand the impact of something on this scale, you would have to look to the science fiction writers, it is incomprehensible.”
The asteroid is currently hurtling around the Earth fifty times faster than a jumbo jet and double the speed of a space rocket..
Though several million miles away astronomers fear a slight deviation from its orbit will put it on a headlong collision course with the planet.
Professor Napier said: “It is a bit like shooting through a key hole.
“All being well this one is far enough away not to do us any harm, but people are concerned because you just don’t know.”
If it were to strike the sea it would send a plume of halogen gasses into the stratosphere destroying the ozone layer, he said.
He added: “This would allow unrestricted sunlight hit the Earth, the sky would heat up becoming strong enough to burn vegetation.
“It would also put a lot of water into the stratosphere with these effects ultimately leading to a mass extinction.”
NASA’s Near Earth Object Programme puts the enormous lump of rock on course to pass within six million miles of Earth on May 14.
In astronomical terms this is a tiny distance and close enough to prompt astronomers to keep an eye on it until is passes safely.
Its exact size is still unclear though it is estimated to be between 580 metres and 1.3km wide – most likely around 680 metres.
In a statement NASA said: “1999 FN53 was discovered on 1999 Mar 31 by the Lowell Observatory Near-Earth Object Search (LONEOS).
“It has an absolute magnitude of 18.3 suggesting a diameter within a factor of two of 680 metres but otherwise its physical properties are poorly known.
Astronomers have named June 30 as Asteroid Day to highlight the dangers of Potentially Dangerous Asteroids (PHAs) hurtling through space.
Initiative co-founder Grigorij Richters warned there are thousands which have not been identified which could ”destroy life”.
He said: “It just takes one asteroid to completely destroy life, not just humanity, but all species.