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Hello, and welcome back to Everyday Science.
Great news! While the odds of a giant asteroid – Asteroid 2024 YR4 – hitting Earth in 2032 were hovering at around 3 per cent last week, they have now been slashed to 0.002 per cent, according to the European Space Agency.
While the threat from this particular space rock is receding, some of my friends were puzzled by the changing odds and have been grilling me about humanity’s options. For answers to these questions and more, read on…
In contrast to the other thousands of other asteroids that Nasa and other space agencies are monitoring, Asteroid 2024 YR4 was discovered only two months ago, by an automated detection system at a Chilean telescope.
It was initially thought to have only a small chance of hitting Earth, but as more telescopes around the world were used to make further observations, more data points were gathered. This gave greater certainty to its orbital path through space.
“In those first few weeks, you’re only covering a small section of its orbit – at that point there are huge uncertainties,” said Professor Danny Steeghs, an astrophysicist at the University of Warwick.
“Rather than a specific trajectory, they give you a distribution of possible trajectories. You ask how many of these trajectories would intersect the Earth – this is where the quoted probabilities come from. The calculations were run very often in the first weeks to months, whenever there was an additional data point that could inform a better calculation.”
Such a risk is “highly unlikely”, said Professor Steeghs. The asteroid, which takes about four years to circle the Sun, is currently travelling away from Earth, meaning that by April, it will become impossible to get more data for another three years, until it re-approaches in June 2028.
Fortunately, enough observations were made since December that we won’t spend the next three years on tenterhooks. “We did well in securing enough in these past few weeks that the more dramatic scenarios are not [likely],” said Professor Steeghs. “Now it’s clearly going towards zero. There’s no expectation that it will shoot back up.”
In the past few years, we have taken several steps towards preparing for the detection of a dangerous asteroid. Multiple bodies, such as Nasa and the European Space Agency have plans in place.
The need for action would depend on the size of the incoming rock. Asteroid 2024 YR4 is thought to be between 40 and 90 metres in diametre. This is nowhere near as big as the asteroid that finished off the dinosaurs – which was more like 10 to 15 kilometres wide.
But YR4 could still cause severe damage if it landed in an inhabited region. Just how much would depend on its exact size.
If it is 40 metres wide, this is twice as big – although eight times the mass – as the meteor that impacted over Chelyabinsk, Russia, in 2013. This exploded in the air, damaging buildings but causing no deaths. On the other hand, if the asteroid is 90 metres wide, it would be what is sometimes called a “city killer”.
In March, Nasa will turn the mighty James Webb Space Telescope onto Asteroid 2024 YR4, which should give us a more accurate estimate of its size. This will shed light on what our options would have been, even though any action now looks unlikely.
While in the 1998 movie Armageddon, a team of miners led by Bruce Willis blow up an incoming asteroid with a nuclear bomb, in real life this would be inadvisable, said Professor Steeghs. “You’re going to turn one big rock [into] 10 rocks, probably covering a much larger area of impact on the earth than the original one. So you’ve actually made it worse.”
Instead, the best option is to deflect the asteroid from its course. Methods could include crashlanding a spacecraft onto the rock, firing lasers at it or covering it with a shiny material that would reflect the Sun’s rays, giving a weak push that would build over time.
The more warning we have, the smaller a nudge that is needed. Options also depend on what the asteroid made of – if it is brittle, a hard push might risk the rock breaking up. “You don’t know whether there are fissures in the asteroid, whether it might fragment into two chunks, said Professor Martin Ward, an astrophysicist at the University of Durham.
Three years ago, Nasa carried out the first mission to change an asteroid’s course, when the agency smashed a small probe into an asteroid called Dimorphos. The experiment worked, in that the rock’s orbit changed – although that was more due to the asteroid ejecting a plume of dust. “That outgassing achieved more of a deflection than the initial kick,” said Professor Steeghs.
The result of the experiment has suggested a new deflection method, of causing such outgassing deliberately, by damaging the rock’s surface. “It’s a slightly more controlled method, because you don’t just fire [something] at it and hope it works,” said Professor Steeghs. “You would fly alongside the asteroid and try to control the process until you’ve achieved what you need to do.”
If you have seen headlines this week saying that a study has found antidepressants make dementia progress faster, don’t panic. The researchers themselves, as well as other experts, say that any effect is not yet proven and even if real, would be so small as to be barely noticeable.
One of my favourite popular science writers is US author Mary Roach, whose genre might best be described as biological comedy. I had somehow missed the publication of her 2021 book, Animal Vegetable Criminal, on the ways that wildlife and humanity come into conflict.
Roach’s quirky tales are full of gentle humour and thought-provoking insights into animal behaviour, perfect for my bedtime reading.
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