NASA on Wednesday sharply downgraded the threat that a massive asteroid could slam into Earth in 2036.

Apophis, which captured widespread attention when it was discovered in 2004 and it was learned that it might pose a threat to Earth, is two and a half times the size of a football field.

There is now a one-in-250,000 chance of a collision with Earth in 2036 -- sharply down from an earlier estimate of a one-in-45,000-chance, according to new calculations by Steve Chesley and Paul Chodas of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, based on new techniques and data.

They will present their results at the conference of the American Astronomical Society in Puerto Rico on October 8.

"The refined orbital determination further reinforces that Apophis is an asteroid we can look to as an opportunity for exciting science and not something that should be feared," Don Yeomans, manager of the Near-Earth Object Program Office at JPL, said in a statement.

At first, astronomers worried the 885-foot (270-meter) asteroid had a 2.7 percent chance of colliding with Earth in 2029. Later calculations ruled out a collision in that year.

Apophis is slated to sail no closer than 18,300 miles (29,450 kilometers) above Earth's surface on April 13, 2029.