Can the ‘city-killer’ asteroid which could destroy Kolkata, Mumbai be stopped?

Is the ‘city-killer’ asteroid likely to hit Earth in 2032?

While the risk remains low, Nasa data indicates that the potential impact corridor of the asteroid spans the eastern Pacific Ocean, northern South America, the Atlantic Ocean, Africa, the Arabian Sea, and South Asia.

What does this mean?

This suggests that seven of the world’s most populated cities, which include Mumbai, Kolkata, Dhaka, Bogotá, Abidjan, Lagos, and Khartoum, could be vulnerable if the asteroid were to strike.

Though the chances of this asteroid impacting Earth are minimal, experts point out that it is powerful enough to destroy an entire city.

However, even if it were on a collision course, scientists believe humanity now has the capability to defend against such threats.

New observations of asteroid 2024 YR4 helped us update its chance of impact in 2032. The current probability is 1.5%.

Our understanding of the asteroid's path improves with every observation. We'll keep you posted. https://t.co/LuRwg1eaCv pic.twitter.com/SfZIxflB95

— NASA (@NASA) February 20, 2025

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On Tuesday, Nasa announced that the probability of the recently discovered asteroid striking Earth on December 22, 2032, has increased to 3.1 per cent - marking the highest probability for a large asteroid in modern predictions.

Before proceeding further, it is important to understand what an asteroid is.

What is an asteroid?

Asteroids are rocky bodies that orbit the sun, significantly smaller than planets. Scientists believe they are remnants from the solar system’s formation about 4.6 billion years ago.

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Millions of asteroids are concentrated in the region between Mars and Jupiter, known as the main asteroid belt. Occasionally, gravitational forces push them out of this region, causing them to travel unpredictably - like the one currently being tracked.

What is being done about the ‘city killer’ asteroid?

Experts suggest that if the asteroid does not collide with Earth, it may still detonate in the atmosphere with an estimated force of around eight megatons of TNT. This would be over 500 times more powerful than the Hiroshima bomb, making it the most dangerous space rock identified through modern forecasting.

Unlike the six-mile-wide asteroid that led to the extinction of dinosaurs 66 million years ago, 2024 YR4 falls under the category of a ‘city killer.’

While not large enough to threaten the entire planet, it has the potential to cause massive destruction to a city.

“Don’t panic,” Richard Moissl, head of the European Space Agency’s planetary defence office, told AFP.

As astronomers continue to gather data, the likelihood of a direct impact is expected to increase temporarily before eventually dropping to zero.

Even in the highly unlikely scenario that the probability reaches 100 percent, “we are not defenceless,” Moissl stressed.

Here are some of the methods scientists could use to deflect or eliminate the asteroid known as 2024 YR4.

How the asteroid can be destroyed

Hit it with a spacecraft

Only one planetary defence strategy has been tried out on an actual asteroid.

In 2022, NASA’s Double Asteroid Redirection Test (DART) deliberately smashed a spacecraft into the 160-metre-wide Dimorphos asteroid, successfully altering its orbit around a larger space rock.

An advantage of this plan is that we could hit the 2024 YR4 asteroid with multiple spacecrafts, observing how each one changed its trajectory, Bruce Betts, chief scientist for the nonprofit Planetary Society, told AFP.

The asteroid discovered in December is estimated to be 40-90 metres wide – roughly half the size of Dimorphos.

“You have to take care not to overdo it,” Moissl warned.

If the spacecraft partially destroyed the asteroid, it could send “bits flying off” that still head towards Earth, he said.

If this kind of mishap changed the eventual impact site on Earth – for example, “from Paris to Moscow” – that would likely cause major problems back home, Betts added.

Gravity tractor, ions and spray painting

A separate idea called a gravity tractor involves a large spacecraft flying up near the asteroid and – without touching it – using its gravitational pull to tug it away from Earth.

Another non-contact plan would put a spacecraft near the asteroid armed with thrusters that would exert a “constant stream of ions” to shove the asteroid off course, Moissl said.

Scientists have also considered spray painting one side of the asteroid white, increasing its reflectiveness so it slowly changes trajectory.

These subtler strategies would require reaching the asteroid sooner than for some more severe options.

Nuclear bombing?

Or we could also just blow it up with a nuclear bomb.

Rather than drilling a nuclear weapon deep into an asteroid – as depicted in the 1998 sci-fi action movie “Armageddon” – this would likely involving detonating a bomb nearby.

Last year, US researchers testing out this theory on a marble-sized mock asteroid in the lab found that the x-rays from a nuclear blast would vaporise its surface and send it shooting off in the opposite direction.

Even setting aside the ethical, political and legal issues of sending nukes into space, this is considered more of a last-ditch plan for kilometres-wide asteroids like the one that killed off the dinosaurs.

And again, there is a risk that a nuclear explosion could still send unpredictable chunks hurtling towards Earth.

Lasers might help

Along less dangerous but similar lines, another idea is to shoot laser beams from a spacecraft to vaporise the side of an asteroid, pushing it away.

Lab experiments suggest this plan is viable, but it is not one of the “top techniques” being looked at, Betts said.

What if these options fail?

If necessary, deflecting this asteroid is “doable, but it depends on the speed at which we move as a planet”, Moissl said.

While experts and space agencies will make their recommendations, ultimately the decision on how to tackle the asteroid will be made by world leaders.

If all else fails, we will have a good idea of the strike zone of the asteroid – which is not a “planet killer” and at most could threaten a city, Moissl said.

This means that preparing for impact, potentially including evacuation if the area is populated, will be the last line of defence.

“Seven and a half years is a long time to prepare,” Moissl said, re-emphasising that there is a roughly 97 percent chance the asteroid will miss Earth.

With inputs from AFP