(Sen) - NASA is seeking to allay fears that a sizeable asteroid will collide with the Earth in 2040. A special international workshop attended by scientists and engineers has concluded that the chance of an impact is only one in 500.
But astronomers will make detailed observations with giant telescopes and Hubble in space over the next two years and discussions have also centred on how the asteroid might be deflected if it is confirmed to be a threat.
The possibility of a collision was raised following the discovery of asteroid 2011 AG5 by an automatic camera on Mt Lemmon, Arizona, that is part of the NASA-sponsored Catalina Sky Survey, on January 8 last year.
The space rock was estimated to be about 140 metres wide and would produce an explosion with the force of 11 megatons of energy if it should hit the Earth's southern hemisphere on its approach on February 5 2040.
But whether or not an impact occurs depends on what happens 17 years earlier when the asteroid makes a close flyby of Earth on February 3, 2023.
If it should pass through what is termed a 365 km wide "keyhole" 1.8 million km from the Earth on that date, then an impact in 2040 will be a real possibility.
The asteroid has not been observed since September 21 last year after which it became too distant and faint to see in the glare around the Sun. But experts have been working with observations made since its discovery plus some images subsequently found on another sky survey, called PanSTARRS, that were taken in the previous months.
Even so, they have still only been able to log the cosmic missile's position over around half its orbit of 625 days. Experts gathered at NASA's Goddard Space Flight Center in Maryland to discuss the data.
Their report says: "When 2011 AG5 emerges from the daytime sky and is observed again, its orbit will be recalculated and its orbital motion will become much better defined. The uncertainty in the asteroid’s predicted position in 2040 will then shrink, and in all likelihood, the probability of Earth impact will drop to essentially zero.
"But there is a small chance that the nominal predicted position in 2040 could get even closer to the Earth, in which case the impact probability could rise to as high as 10-15 per cent."
The giant 10-metre Keck telescopes on Hawaii are likely to be turned on the asteroid in October this year to find out more about it. But a year later, when it is in a darker sky NASA plans to view it with the Hubble space telescope.
The workshop's report considers the possibility that the asteroid could be deflected by sending a space probe to impact with it if it is eventually found to be on collision course. But it also considers using rocket or solar propulsion to steer it away from Earth.
Lindley Johnson, of NASA's Near-Earth Object (NEO) Observation Program, said: "While there is general consensus there is only a very small chance that we could be dealing with a real impact scenario for this object, we will still be watchful and ready to take further action if additional observations indicate it is warranted."
He added: "Given our current understanding of this asteroid's orbit, there is only a very remote chance of this keyhole passage even occurring."