Although no one noticed at the time, the Earth was almost hit by an asteroid last Friday.

The previously undiscovered asteroid came within 8,700miles of Earth but astronomers noticed it only 15 hours before it made its closest approach.

Its orbit brought it 30 times nearer than the Moon, which is 250,000 miles away.

But before you head for the nuclear bunkers you will be relieved to learn the tumbling rock was only 23ft across. Similar sized objects pass by this close to Earth about twice a year and impact on the planet about once every five years.

Astronomers believe the object, called 2009 VA, would have almost completely burned up while entering Earth's atmosphere, causing a brilliant fireball in the sky but no major damage to the surface. 

The asteroid was discovered by the Catalina Sky Survey on November 6, 2009. It was then identified by the Minor Planet Centre in Cambridge, Massachusetts as a near Earth object. 

The path of the asteroid 2009 VA, which passed well within the Moon's orbit last Friday

Nasa's Near Earth Object Programme plotted the orbit of the object and determined that although it would fly extremely close to our planet it wouldn't hit us.

It was the third-closest known (non-impacting) Earth approach on record for a cataloged asteroid.

The Nasa NEO programme aims to detect and track at least 90 per cent of the 1,000 asteroids and comets that approach Earth and are larger than 0.6miles in diameter, by 2020.

They monitored a 100ft asteroid that whizzed 45,000 miles above the Earth's surface on March 2 this year. A similar sized object slammed into Tunguska, Siberia in 1908. The impact created a blast so powerful it levelled 1,200 square miles of forest.