Another asteroid to pass close to Earth

An asteroid is set to pass between Earth and the moon on Saturday morning - the second space rock to buzz us this week.

File image: NASA depicts the OSIRIS-REx spacecraft and the Earth. Source: AAP

Another asteroid is headed our way - the second this week - but there is no need to worry.

The newly discovered space rock will pass within 64,000km of Earth about 9.30am on Saturday AEDT, less than one-fifth the distance to the moon.

Designated 2018 CB, the asteroid is an estimated to be 15-40m in size, possibly bigger than the one that exploded over Russia five years ago this month.

The manager of NASA's Center for Near-Earth Object Studies , Paul Chodas, says asteroids this size usually do not come this close - just once or twice a year.

While Saturday's close approach is not a big deal, Chodas said in an email "it is a reminder that asteroids can pass very close to our planet and it's important that we find these objects when they do get close".

It will be the second time this week an asteroid has buzzed Earth. On Wednesday morning AEDT, an asteroid passed within 184,000km, slightly more than halfway to the moon.

Both this week's asteroids were discovered February 4 by astronomers at the NASA-funded Catalina Sky Survey in Arizona.

Last year, more than 2000 previously unknown near-Earth asteroids were discovered, Chodas said.