If the nearly 275-metre-wide Apophis passes through a narrow gravitational keyhole in April 2029 it will be on course for a massive collision seven years later, most likely on April 13, 2036, the scientists said.
The force of earth`s gravity is so great that if the asteroid goes through the hole its path could be "tweaked"-- sending it straight towards us and there was a chance that it collide with Earth, said Donald Yeomans, head of NASA`s Near Earth Object Program office.
"The situation is that in 2029, April 13, Apophis flies very close to the Earth, within five Earth radii, so that will be quite an event, but we have already ruled out the possibility of it hitting at that time," Daily Mail quoted him as saying to a science website `Life`s Little Mysteries`.
"On the other hand, if it goes through what we call a keyhole during that close Earth approach. Then it will indeed be perturbed just right so that it will come back and smack Earth on April 13, 2036."
The NASA scientist, however, said such a collision is unlikely although Russian scientists are predicting the asteroid may strike earth in 2036.
Professor Leonid Sokolov of the St Petersburg State University has earlier said that `Apophis` could approach Earth at a distance of 37,000-38,000 kilometres (per hour) on April 13, 2029.
"Its likely collision with Earth may occur on April 13, 2036. Our task is to consider various alternatives and develop scenarios and plans of action depending on the results of further observations of Apophis," Prof Sokolov was quoted as saying.
Russian scientists held a meeting 14 months ago to look at launching an operation to knock the asteroid off path.
However, US scientists have estimated the actual chance of it happening is one in 250,000. Although it is big enough to cause a lot of damage to the planet it would not bring about the Armageddon.
If it is discovered that Apophis is on course to crash into the earth, NASA would attempt to take evasive action to change its path. The easiest way of doing this would be to crash an unmanned spaceship into the asteroid, the scientist said.
In July 2005 Deep Impact crashed into comet Tempel 1 in an operation to study the interior of a comet. The mission revealed that a comet`s nucleus is more dusty and less icy than had been believed.