Asteroid safely passes by the Earth

A wayward asteroid has safely passed Earth this evening, making its closest approach some 28,000km above earth.

"Asteroid #2012DA14 has made its closest approach to Earth, safely passing our planet 17,500 miles above Indonesia. It's now headed away," Nasa tweeted at about 8pm.

The asteroid passed  at about 7.25pm and was closer than some of the Earth's orbiting satellites, looking something like a fast moving star, but only because it is so very close.

Telescope images from western Australia, broadcast on NASA Television, showed the asteroid as a white speck against the blackness of space.

The Asteroid "passed inside the ring of geosynchronous weather and communications satellites," Nasa said. The space agency has released a photograph of the asteroid's path taken from an Australian observatory.

The asteroid is one of thousands of "near earth objects" that buzz around this part of the solar system. Many cross our path as we orbit the sun, but happily none have our name on them so they sail by with no consequence. But that doesn't mean that bodies such as the US National Aeronautics and Space Administration and the European Space Agency aren't interested. Anything but.

Asteroid 2012DA14 is only 50m across, a mighty big rock but just a dot compared to the Earth. Even so it would give off a stupendous bang if its course was slightly different and on a collision course with earth. If it did decide to call by we would know all about it, says Terry Moseley of the IAA. Barrelling into the atmosphere would heat it up to colossal temperatures and then depending on how hard a rock it is, would smash into the earth, Mr Moseley said.

Any impact would unleash an explosion equivalent to 2.4 million tonnes of TNT, wiping out everything for thousands of kilometres around the impact site

Part of the reason for its destructive power is its speed. It is clipping along at about 27,000 km/h so it carries along a lot of potential energy.

This is why international programmes have been set up to watch for near earth objects. Several thousand are known and these whizz by otherwise unnoticed far enough away to be beyond the lunar orbit. The watchers however don't lose sleep over these, they worry instead about the one's we haven't discovered yet, the ones that appear without warning out of the darkness of space.

So far our experience of near earth objects has more to do with Hollywood than anything else, but the watchers maintain their vigil for the one we can't dodge.

Travelling at between 20,000km/h and 30,000km/h - around 8km a second, or eight times the speed of a rifle bullet - the asteroid flew inside the orbits of high geostationary satellites some 35,406km above the Earth. Precise calculations show there was absolutely no possibility of DA14 hitting the Earth.

But scientists have a good idea of what the effect of such an impact would be because a similar-sized meteor devastated a remote region of Siberia in 1908, flattening forest  over an area of 2,150 sq km. Exploding a short distance above the ground over Tunguska, the object generated a blast 1,000 times more powerful than the atom bomb dropped on Hiroshima.

The American space agency Nasa has plans for a future mission called Dart which will fire a probe at an asteroid to see if it can be moved.

Fewer than 10,000 of the asteroids which could one day pose a threat to the Earth have so far been identified. This is less than 10 per cent of all the objects that may be out there, according to Dr Lindley Johnson, head of Nasa's Near Earth Objects observations programme.

See tips for viewing tonight's passing asteroid here.

Additional reporting: PA