The pock-faced Moon has a new crater after a 400-kilogram meteorite slammed into its surface, creating a flash of light that could be seen from Earth.
Travelling at 61,000kmh, the rock, which was about one-metre in diameter, left a depression about 40-metres wide in what is thought to be the largest lunar impact ever recorded, the Guardian said today.
The collision created a flare lasting eight seconds that would have been visible to the naked eye, given good viewing conditions.
The impact energy was equivalent to 15 tonnes of TNT - at least three times greater than that of another lunar impact observed by Nasa in March last year.
Unlike Earth, the moon has no atmosphere to protect it from incoming meteorites.
The event was seen by Jose Madiedo when he was operating two Spanish lunar-observing telescopes on September 11 last year, and has been reported by at Britain's Royal Astronomical Society.
"When I saw it on the screen I realised I had witnessed a rare and unusual event. It was really huge. I couldn't imagine such a bright event," Madiedo told the Guardian.
"We image a lot of impacts on the moon, but they're caused by very small rocks. They can be the size of a nut, and just a few grammes, and go up to 1kg. But this event was really impressive and very rare."
By observing the moon, Madiedo hoped to learn more about threats to Earth.
"We are very close neighbours," he said.
"What happens on the moon can also happen on the Earth. This impact . . . shows that the rate of impacts on our planet for rocks of this size, around one metre in diameter, is about 10 times greater than we thought."
However, he said most rocks this size would be destroyed before hitting Earth as they burned up in the atmosphere. Any surviving rock would not pose a serious threat.
The asteroid that exploded over Chelyabinsk in Russia in February last year was estimated to be about 19m wide.
It hit the atmosphere with energy estimated to be equivalent to 500,000 tonnes of TNT, sending a shockwave twice around the globe. It caused widespread damage and injured more than 1,000 people.
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