Odds of asteroid 2024 YR4 hitting Earth in 2032 have fallen again

NASA has downgraded the risk of asteroid 2024 YR4 hitting Earth in 2032 to 1.5 per cent, or 1-in-67, down from a high of a 1-in-32 chance, which was the highest odds yet of collision.

Astronomers discovered that the asteroid was barrelling towards Earth in December and it has been a focus of the world’s telescopes and space agencies ever since. As they gather more data on the asteroid’s precise orbit, astronomers have been able to calculate the likelihood of it hitting Earth with greater precision. The asteroid is thought to be between 40 and 90 metres wide and has the potential to release energy equivalent to 7.7 megatonnes of TNT should it hit Earth – enough to destroy a city.

According to NASA, the odds of collision in 2032 have been edging up from a 1-in-83 chance since it was first spotted. It has since moved to 1-in-67, to 1-in-53, to 1-in-43, to 1-in-38, to 1-in-32 and now falling back to 1-in-67. The European Space Agency has slightly different odds, currently giving the asteroid a 1.38 per cent chance of collision. These changes reflect our growing understanding of the asteroid’s path, rather than necessarily meaning it is any more or less likely to hit Earth.

But we are running out of time to forecast the asteroid’s risk. One issue is that 2024 YR4 will fly behind the sun in April, placing it out of the view of most Earth-based telescopes. That limits how much astronomers can refine their predictions, says Hugh Lewis at the University of Southampton, UK..  “Any observations we can make between now and when it’s out of view will obviously help us to refine the orbit and to make better predictions. That doesn’t necessarily mean that it will go down before April. It could continue to go up, but still ultimately miss us.”

Once the asteroid does fly out of view, it is unlikely that we will gain any more information before it comes into view again in 2028. However, astronomers could comb through past data to uncover previously overlooked observations of the asteroid, which would help refine its trajectory. That process is already being undertaken by the world’s space agencies, says Lewis.

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Crucial information on the asteroid’s size and composition will hopefully be gathered by the James Webb Space Telescope in the coming months, says Lewis. This will help us understand whether the asteroid could make it through Earth’s atmosphere intact and how large an explosion it could cause if it does make impact.

“That will help us determine what we need to do about it, because if it’s a stony asteroid, that’s very different from a high proportion of iron-metal asteroid,” says Lewis. An iron-rich asteroid would be worse, as a stony asteroid would potentially break up during impact. “The mass makes a huge difference in terms of the energy and whether or not the atmosphere has an effect on it.”

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