This may be 15 times the distance between the Earth and the moon - or more than 9000 trips between Auckland and Wellington - but will be near enough for scientists to scan it with a giant radar and detail its features right down to metres.
Scientists have identified nearly 10,000 NEOs - a tiny fraction of the total flying about in space - and around 1400 have been classified as hazards.
Yet the chances of impact are tiny, and researchers estimate a 1.5km asteroid or comet would hit the Earth once every million years on average.
University of Auckland lecturer Dr Philip Sharp said when gauging intervals between collisions, the bigger the object meant the longer the wait.
"If you are looking at something like 10km in diameter - like the one that wiped out the dinosaurs - then there's going to be millions of years between such collisions, maybe tens of millions of years."
The effects of such a collision would last for decades, he said.
An asteroid 10km in diameter could fire off around 100,000km of material into the atmosphere, with the lighter particles lingering for years, blocking out the sun, reducing photosynthesis, warming the planet and causing acid rain.
If it still existed, society could begin to recover when the dust finally settled decades later.
Scientists have looked at how such asteroids - those more than 1km wide would be considered to have global-scale impacts - could be deflected away from the planet.
Dramatic concepts include painting one side of an asteroid to influence the effect of sunlight-induced energy on its orbit, or nudging it off course with nuclear blasts.
"You've got to plan many, many years ahead - so it's not like the movie Armageddon, where you can fix it up in the last 10 minutes."
There are even lofty plans to mine asteroids for their raw materials - one such enterprise involving filmmaker James Cameron and Google's Larry Page and Eric Schmidt was launched last month.
Dr Sharp said a notable NEO, the Apophis asteroid, was due to pass at a distance of just 37,000km above the surface of the planet.
"That's the height of the geostationary satellites - so that's close."
The asteroid caused a scare when it was thought there was a small chance it could strike Earth in 2029, but that has since been ruled out.
In 2016, Nasa will launch a robotic sample return mission to one of the most potentially hazardous known NEOs, asteroid Bennu.
The asteroid comes within 500,000km of the Earth every six years and scientists have calculated that in 2182 there is a one-in-1800 chance of the object colliding.
Close encounters
Near-Earth Objects (NEOs) are comets and asteroids that have been nudged by the gravitational attraction of nearby planets into orbits that allow them to enter the Earth's neighbourhood.
Composed mostly of ice with embedded dust particles, comets originally formed in the cold outer planetary system while most of the rocky asteroids formed in the warmer inner solar system between the orbits of Mars and Jupiter. The scientific interest in comets and asteroids is due largely to their status as the relatively unchanged remnant debris from the solar system formation process some 4.6 billion years ago.
- Source: Nasa
