Thailand will have a close encounter with an asteroid expected to move closer to the Earth than the moon in the next 29 years, according to a prominent astronomer Worawit Tanwutthibundit. The asteroid, named 99942 Apophis, will come into close orbit with the Earth 22 years from now and it will come by again, even closer, seven years after that.

This has sparked fears over the possibility that it could collide with the Earth.

Mr Worawit, an executive member of the Thai Astronomical Society, said the asteroid will come within about 34,400 kilometres of the Earth on April 13, 2029.

He cited a report released by the US National Aeronautics and Space Administration (Nasa).

On that day, the asteroid will make its closest approach to the Earth, about eleven times closer than the moon will pass by _ for the first time in 1,000 years, according to Mr Worawit.

The astronomer said the asteroid's visit on that day will provide a basis for calculations about whether it could hit the Earth in the future.

The same asteroid is predicted to pass by the Earth again on April 13, 2036 and it will be even closer then, Mr Worawit said, citing the Nasa report.

He said the calculations will determine whether the asteroid would be on a collision course with the Earth in 2036 or not. ''If it struck the Earth on that day (April 13, 2036), the possible target would be the northern part of Mexico.

''The impact of the collision would be like the power of 870 megatonnes of TNT going off,'' Mr Worawit said.

Mr Worawit said 99942 Apophis is 320 metres in diameter, and orbits the sun every 323 days.

On April 13, 2029, the asteroid will come into view at dusk at a 42-degree angle in the western sky in the constellation Cancer, Mr Worawit said.

It will be able to be observed in the Middle East, Europe, Africa and Thailand.

The 99942 Apophis asteroid was discovered in June 2004. It was then called 2004 MN4.