THE odds of a “city killer” asteroid that once threatened Earth instead smashing into the moon have just doubled.
YR4 was feared to be on a deadly collision course with our planet, with the chance peaking at 20 percent by some estimations.
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Further calculations showed it will, thankfully, sail past without incident when it nears Earth in 2032.
The rock approaches Earth once every four years, and the 2032 cycle will bring it closer than ever before.
Whilst Earth is in the clear, there is a new threat from the speeding space rock.
Physicists say there is a significant chance it could smash into the moon – our only orbital satellite.
And the odds of that happening have doubled since February – now sitting at 1-in-26, or a 3.8 percent chance.
With the building-sized asteroid racing through space at 17km per second, it would pack a serious punch if it collided with the moon.
Astronomers have explained what the consequences might be for Earth.
David Rankin, an operations engineer for the University of Arizona’s Catalina Sky Survey, told the New Scientist a moon smash could “eject some material back out that could hit the Earth”.
The super-speed collision would have the same amount of force as 340 nuclear bombs – and the explosion would be so bright we would likely see it from Earth.
WHY DID THE THREAT TO EARTH DISAPPEAR?
For a few weeks, the world watched in horror as the probability of a “city killer” asteroid called YR4 hitting Earth crept up and up.
At the height of the anxiety, Nasa reportedly feared the chances of a collision could rise past 20 percent – before it plunged to almost zero.
Luca Conversi, an ESA scientist, explained why the probability of YR4 striking Earth changed so dramatically.
He told The Sun: “When we are trying to foresee where an object will be in many years time there is a lot of uncertainty.
“The uncertainty shrinks as we take more data.”
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Luca explained that, to begin with, physicists calculated an area of around a million kilometres where YR4 could travel.
Earth took up about one percent of the possible path zone – so the chance of an impact was said to be one percent.
With more calculations the area decreased.
This meant that Earth took up more of the possible path zone – and so the probability of a strike increased.
That continued until the zone shrank even further, and Earth was eventually outside the possible path.
At that point, the probability plunged to virtually nothing.
Luca said: “That is what happens every single time, unless the object is actually going to hit Earth.”
Even though the process was predictable, Luca said YR4 “was not a false alarm”.
He said a threat like YR4 only comes “once every 20 years or so” – so the world was right to take it seriously.
YR4 now has more chance of hitting the moon than Earth – standing at about 1.7 percent.
Luca said: “If that happened it would be a fantastic thing to see, but wouldn’t pose any danger to us.”
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