It should pass at a distance of about 4 million miles (Science Photo Library)

Nasa is constantly on the lookout for asteroids that may pose a threat to life on Earth.

These so-called near-Earth objects (NEOs) need to pass within a certain threshold to be considered potentially hazardous.

And the experts at the US space agency say there is one such rock on the radar for this week. The asteroid 2012 XA133 is set to pass Earth on Thursday, March 26 at a speed of 53,000mph.

The asteroid measures approximately 1,280 feet (390m) wide, which is enough to cause a major impact on Earth if it collided with the planet. Thankfully, Nasa engineers calculate the trajectory of the asteroid will take it safely past us.

Its believed to pass 0.04453 astronomical units (AU) or roughly 4.1 million miles from the center of Earth. A single AU describes the distance from Earth to the sun roughly 93 million miles.

As they orbit the Sun, NEOs can occasionally approach close to Earth, Nasa explained.

Note that a close passage astronomically can be very far away in human terms: millions or even tens of millions of kilometres.

Alongside Nasa, the European Space Agency (ESA) is also tracking the asteroid. Its actually one of about six that are being tracked as they pass Earth this week but its the only one falling into the potentially hazardous category.

Potentially Hazardous Asteroids (PHAs) are currently defined based on parameters that measure the asteroids potential to make threatening close approaches to the Earth, Nasa said in a statement.

On a daily basis, about one hundred tons of interplanetary material drifts down to the Earths surface, said Nasas Center for Near-Earth Object Studies (CNEOS).

Most of the smallest interplanetary particles that reach the Earths surface are the tiny dust particles that are released by comets as their ices vaporize in the solar neighborhood.

The vast majority of the larger interplanetary material that reaches the Earths surface originates as the collision fragments of asteroids that have run into one another some eons ago.

The agency does go into some detail about would would happen if one of these rocks did end up smashing into us: With an average interval of about 10,000 years, rocky or iron asteroids larger than about 100 meters would be expected to reach the Earths surface and cause local disasters or produce the tidal waves that can inundate low lying coastal areas.

On an average of every several hundred thousand years or so, asteroids larger than a kilometer could cause global disasters. In this case, the impact debris would spread throughout the Earths atmosphere so that plant life would suffer from acid rain, partial blocking of sunlight, and from the firestorms resulting from heated impact debris raining back down upon the Earths surface.

Since their orbital paths often cross that of the Earth, collisions with near-Earth objects have occurred in the past and we should remain alert to the possibility of future close Earth approaches. It seems prudent to mount efforts to discover and study these objects, to characterize their sizes, compositions and structures and to keep an eye upon their future trajectories.

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Nasa: 'potentially hazardous' asteroid will skim Earth this week - Metro.co.uk