What would happen if a ‘city-killer’ asteroid hit the moon?

We all know what happens when an asteroid hits the Earth – Armageddon, pretty much.

One (or maybe two, depending on who you ask) of these massive space rocks killed off the dinosaurs 66 million years ago.

Then last year, the world had a bit of a fright when it looked like there was a tiny chance that a ‘city killer’ asteroid could smash into us in 2032.

While scientists have since said the Earth is safe from the rock, called 2024 YR4, there’s still a chance it will collide with the moon instead.

What would happen if 2024 YR4 smashes into the moon?

The rock’s odds of crashing into our moon are about 4.3%, NASA said last year.

A new paper says that such an impact would be the equivalent of detonating 6.5 megatons of TNT – about 430 times the Hiroshima bomb.

They figured this out by looking at the asteroid’s mass and the energy that would be released if it struck the moon’s surface, called kinetic energy.

This impact would cause a magnitude five earthquake and leave a 0.6-mile crater, making it ‘the most energetic lunar impact event ever recorded’.

Star-gazers would see a bright flash lasting several minutes, followed by hours of ‘infrared afterglow’ as the molten rock cools.

The impact would be visible across the Pacific hemisphere of Earth, they estimate.

Scientists have previously said that, if that does happen, it would ‘be the largest impact in approximately 5,000 years’.

The impact would chuck about 100,000,000kg of lunar material out into the cosmos.

All the lunar dirt could cause dazzling meteor showers down below on Earth, Dr Alfredo Carpineti, an astrophysicist and space and physics editor at IFLScience, tells Metro.

What is 2024 YR4?

Just after Christmas Day in 2024, astronomers spotted something whooshing away from Earth: a rock about 330 feet long.

They plotted its rough trajectory and realised that the odds of it hitting Earth on December 22, 2032, were 1.3% before rising to 3.1%.

These percentages may sound small, but the probability was higher than any ever recorded by NASA for an object like this.

Early estimates of the asteroid’s path show it could slam into or explode over highly-populated areas like Mumbai, India or Bogotá, Lagos.

These days, though, space officials say it’s just 0.00081%, or roughly one in 123,000 chance. This is because astronomers have more information about 2024 YR4 to make more accurate guesses.

While this would be pretty to see, it might not be as much to the satellites that would likely be damaged by all the falling grey rocks.

‘Smaller impacts have been seen on the moon during eclipses,’ the Invisible Rainbows author adds.

‘There’s no danger to us.’

Though researchers say this would be the perfect time to test out Earth’s planetary defences, such as vaporising moon dirt with nuclear explosions.

As scary as a ‘city-killer’ asteroid sounds, a space rock would need to be a fair bit larger to pose a risk to the moon, Dr Carpineti says.

Our ‘dino-killer’ asteroid, which was nearly 5,000 feet long by some estimates, would ‘create a lot of damage’ to our cosmic neighbour.

‘But also, there’s nothing on the moon, so it wouldn’t be a big deal.’

‘There’s nothing out there that could properly destroy the moon,’ Dr Carpineti adds, ‘the moon is very, very, very solid.’

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