Asteroid only spotted on Christmas Day passed Earth yesterday in near-miss

An asteroid the size of a bus has skimmed "close" to Earth at a speed of almost 34,000 kilometres an hour on Thursday after only being spotted on Christmas Day.

The asteroid, named YZ4 2017, was spotted on Monday at a distance of 224,000 kilometres - less than the distance to the Moon and considered a "near-miss" by astronomers.

As it was only spotted on Monday, very little could have been done to protect the planet if it were struck, The Daily Mail reported.

NASA classes asteroids as "hazardous" if they travel within 7,403,000 kilometres of Earth. The Moon is only 384,400km away.

An asteroid the size of a bus has skimmed 'close' to Earth. Photo: Getty
An asteroid the size of a bus has skimmed 'close' to Earth. Photo: Getty

“2017 YZ4 is the 52nd known asteroid to fly by Earth within one lunar distance this year and the first since two such asteroids flew past us on November 21," said Lindley Johnson, a Planetary Defense Officer at NASA's Science Mission Directorate in Washington.

"They varied from 1 to 80 metres in size."

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“As of December 25, there are 17,506 known Near-Earth Objects (NEOs), in orbits around the Sun that could come close to our planet; 17,400 are asteroids and 106 are comets.

“This year, we’ve discovered 1996 Near Earth Asteroids so far. There were 1887 such objects discovered in 2016 and 1566 in 2015."

The asteroid was first spotted at Mount Lemmon Survey Observatory in Arizona.

The asteroid, named YZ4 2017, was spotted on Christmas Day. Photo: NASA
The asteroid, named YZ4 2017, was spotted on Christmas Day. Photo: NASA

NASA already has a program in place that tracks asteroids larger than 1.06km. An object of this size, roughly equivalent to a small mountain, would have global consequences if it struck Earth.

An asteroid about 9.66km in diameter hit Earth some 65 million years ago, triggering climate changes that are believed to have caused the dinosaurs - and most other life on Earth at the time - to suddenly die off.