An asteroid which Nasa says is 'potentially hazardous' is due to fly worryingly close to Earth on Wednesday.
And while there is no chance the 270m-wide rock will hit our planet this week, researchers will use it as a key opportunity to peer more closely at the asteroid's orbit, and learn more about its future trajectory ahead of a potential collision in 2036 and beyond.
If it ever does hit the Earth, researchers say it would unleash an explosion 100,000 times more powerful than the nuclear weapon detonated over Hiroshima.
The asteroid, named Apophis, caused a near panic in 2004 after researchers calculated it had a one in 300 chance of hitting the Earth. The concern rose after more observations showed that the chances of a deadly impact on 13 April 2029 were closer to about 1 in 45.
At that point the asteroid - whose namesake was Gaul's ancient God of death, intent on plunging the world into darkness - seemed as if it had been aptly named.
Fortunately, further images showed that the orbit had been miscalculated - and that the chance of an impact in 2029 was very low indeed.
However, that hasn't removed the danger entirely. The 2029 pass-by is really very close - just 30,000 km from Earth, which is closer than several communication satellites - and there is still a small chance that Apophis will hit the Earth in 2036.
DEADLY SKIES: More than 9,487 near-Earth objects have been discovered so far by scientists at Nasa's Near Earth Object Program.
Using the NEOP's scale of danger (the 'Torino' scale), which stretches from 0 (no chance of impact) to 10 (devastating impact), only two objects discovered so far rate above zero:
- 2011 AG5, an asteroid 460 across, has a one in 500 chance of hitting Earth in 2040
- 2007 VK184, 426 feet wide, has a one in 1,820 chance of hitting us in 2048.
The pass on Wednesday is much less concerning, and the asteroid is scheduled to pass more than 14.5 million kilometres above our heads.
But there is understandably strong interest in examining its rotation and mass more closely, which Wednesday's observations will allow.
Apophis is part of the Aten family of space objects, which are not part of the solar system's largest asteroid belt, and usually orbit the sun inside the orbit of Earth.
Part of the remaining concern is the so-called "Yarkovsky effect", which is the unpredictable spin and momentum created when half of the asteroid is heated by the sun and half is left in freezing darkness. Just how this impacts the path of the asteroid isn't known, meaning that scientists may not know it will hit us until it's too late.
BLOG: Dan Mac: Celebrating Apophis Day
Russia has said it might attempt to place a tracking beaon on the asteroid in 2020 so that it can be more accurately traced.
As such its presence is worrying not just for the threat it represents - but for the other asteroids which similar orbits that also fly around the sun with similar paths.
Another, smaller, rock - 2012 DA14 - will pass by Earth at about 34,000 km in February. That's much closer than Apophis - and several others are scheduled to visit us in 2013.. Keep watching the skies...