The 'doomsday story' started with claims that Nibiru, a supposed planet discovered by the Sumerians, is headed toward Earth, scientists said.
This catastrophe was initially predicted for May 2003, but when nothing happened the doomsday date was moved forward to December 2012 and linked to the end of one of the cycles in the ancient Mayan calendar at the winter solstice in 2012 - hence the predicted doomsday date of December 21, 2012, they said.
The US Space agency also specified that the Mayan calendar does not end in December 2012.
"Just as the calendar you have on your kitchen wall does not cease to exist after December 31, the Mayan calendar does not cease to exist on December 21, 2012," NASA said.
"This date is the end of the Mayan long-count period but then - just as your calendar begins again on January 1 - another long-count period begins for the Mayan calendar," it said.
Scientists also clarified that the rumour of a planet or brown dwarf called Nibiru or Planet X or Eris approaching the Earth and threatening our planet with widespread destruction is just an "Internet hoax".
"Nibiru and other stories about wayward planets are an Internet hoax. There is no factual basis for these claims. If Nibiru or Planet X were real and headed for an encounter with the Earth in 2012, astronomers would have been tracking it for at least the past decade, and it would be visible by now to the naked eye," scientists said.
"Obviously, it does not exist. Eris is real, but it is a dwarf planet similar to Pluto that will remain in the outer
solar system; the closest it can come to Earth is about 4 billion miles," they said.
On danger of Earth being hit by a meteor in 2012, scientists said that NASA astronomers are carrying out a study called the Spaceguard Survey to find any large near-Earth asteroids long before they hit.
"The last big impact was 65 million years ago, and that led to the extinction of the dinosaurs. We have already determined that there are no threatening asteroids as large as the one that killed the dinosaurs," they said.