The asteroid, named Toutatis, flies by Earth every four years. During its closest approach on Wednesday, the celestial rock will pass about 4.3 million miles (7 million km) from Earth, which is about 18 times farther away than the moon.

"There is no danger of a collision with Earth," NASA astronomer Lance Benner said in a statement.

The 0.6-mile (4.3-km) long asteroid circles the sun in an orbit that is very closely aligned with Earth's, making it a potentially hazardous object for the future.

The asteroid was first spotted in 1934 and its orbit was confirmed in 1989. In 2004, Toutatis passed by Earth just four times farther away than the moon, much closer than this week's encounter.

Astronomers are using radar and optical telescopes to get a better fix on the asteroid's location, its unusual spin and the flight path in hopes of refining estimates on where it will travel in the future.

"We already know that Toutatis will not hit Earth for hundreds of years," Benner said. "These new observations will allow us to predict the asteroid's trajectory even farther into the future."

(Reporting by Irene Klotz in Phoenix; Editing by Jane Sutton and Eric Beech)

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