An asteroid has flown within a whisker of Earth - allowing scientists to test our planetary defences

An asteroid flew within a whisker of the Earth earlier this morning, narrowly missing the ring of satellites which surround our planet. The encounter gave scientists a rare opportunity to test the abilities of an international asteroid warning network.

TC4, as the object is known, is travelling at around 16,000 mph and came closest to the Earth's surface at 06:42 when it was 26,000 miles above Antarctica - a little over one tenth of the distance to the moon. Despite its proximity, experts had already mapped TC4 's trajectory and were confident it would miss the planet.

The asteroid is estimated to measure between 15 to 30 meters across, which is relatively small but would still have posed a risk if it had struck Earth. The Chelyabinsk meteor - which is comparable in size - injured more than a thousand people and caused widespread damage to buildings when it exploded over the Russian city in 2013.

TC4 was first spotted in 2012 by a Nasa-funded near Earth object survey called Pan-STARRS and was subsequently kept under close watch by asteroid trackers around the world. They reported their observations to the Minor Planet Center, a worldwide organisation in charge of collecting data for asteroids and comets.

With the help of this type of data, scientists can now accurately predict the trajectories of potentially harmful space objects as they move closer to Earth.

The global asteroid-impact early warning system is a volunteer project run by Pan-STARRS and supported by Nasa's Planetary Defence Coordination Office (PDCO), although astronomers supported by other countries' space agencies also took part.

"Asteroid trackers are using this flyby to test the worldwide asteroid detection and tracking network, assessing our capability to work together in response to finding a potential real asteroid-impact threat," said Michael Kelley, program scientist and NASA PDCO lead for the TC4 observation campaign.

For the test, dozens of professional telescopes around the world made ground-based observations in different wavelengths ranging from visible to near-infrared and radar. Backyard astronomers could also contribute, although TC4 was very difficult to observe without professional equipment.

"This campaign is a team effort that involves more than a dozen observatories, universities and labs around the globe so we can collectively learn the strengths and limitations of our near-Earth object observation capabilities," said Vishnu Reddy, who is leading the TC4 observation campaign.

"This effort will exercise the entire system, to include the initial and follow-up observations, precise orbit determination, and international communications."

While no asteroid currently known is predicted to strike the Earth for the next 100 years, scientists are making preparations that could one day avert disaster when our planet's luck does eventually run out. After all, asteroid impacts can be devastating; the huge space rock that struck the Earth 65 million years ago is thought to have led to the extinction of the dinosaurs.

With enough warning, say 5 or 10 years, a large asteroid headed for Earth could potentially have its trajectory shifted slightly in order steer it away from our planet.