What are the chances of Earth being hit by a big asteroid?

A week ago, the new Vera C. Rubin Observatory released its first images. It also included a video of all the asteroids it discovered. In just 10 hours, the Simonyi Survey Telescope with the Legacy Survey of Space and Time (LSST) camera captured more than 2,000 previously undetected asteroids.

It’s a reminder that, while there’s a lot of space in space, our solar system still has a lot going on.

Asteroids are rocks and debris left over from the formation of our solar system. There are two main areas where much of it is located. The first being the asteroid belt between Mars and Jupiter. The second is the Kuiper Belt, beyond the orbit of Neptune.

But there are still many more floating around out there.

Scientists estimate that roughly 44 tonnes of meteoric debris fall toward Earth every day. That’s right: every day. 

The good news is that most of it burns up in our atmosphere. 

But what are the chances that a much larger object is on a collision course with Earth?

“Earth has been hit in the past by large asteroids, and presumably, if we waited long enough, something would happen. But the risk is very, very small,” said Paul Weigert, a professor at Western University’s department of physics and astronomy in London, Ont.  

“So none of the asteroids that we know about today have a significant chance of striking Earth in the next 100 years or so. So that’s a pretty healthy time horizon.”

However, there’s no guarantee that something that has thus far been undetected isn’t on its way.

“As we go beyond that, there’s always the chance that we can discover new asteroids, of course, and they become not unpredictable, but harder to predict in great detail, at longer distances,” Weigert added.

The importance of being earnest

There are numerous groups scanning the sky looking for asteroids, and Weigert said that the Vera C. Rubin Observatory ramps up the search like never before.

“The Vera Rubin telescope is really going to revolutionize the way this kind of work is done. I think even people who knew what to expect, that knew this was coming down the pipeline, were impressed by the way LSST-Rubin was able really dive right in and start finding these things,” he said. “So that’s going to be a very impressive discovery machine going forward.”

NASA has found more than 1.4 billion asteroids, and believes it has identified more than 95 per cent of asteroids one kilometre or larger in our solar system.

It’s estimated that the Rubin observatory will discover 89,000 near-Earth objects and 3.7 million main-belt asteroids.

Now, getting hit by an asteroid is a really a matter of odds.

Smaller objects, such as asteroids about 10 metres in diameter impact Earth once a decade. While not planetary ending, they can break windows. The Chelyabinsk meteorite that exploded over Russia in 2013 was twice this size, and did indeed break windows, which injured roughly 1,500 people. 

WATCH | News report on 2013 meteorite that struck Russia 

The bigger the rock, the less often they impact Earth. For example, a 140-metre asteroid impacts Earth roughly once every 1,000 years and one that is about one kilometre in size impacts Earth roughly every 700,000 years. An asteroid that size would be devastating.

The one that is believed to have killed off the dinosaurs was about 10 to 15 kilometres in size. Those impacts are estimated to happen about once every 100 million years.

Jim Freemantle is project manager for the OSIRIS-REx laser altimeter project at York University in Toronto. OSIRIS-REx was the sample-return mission to the asteroid Bennu. He has a tiny piece of the asteroid in his lab.

He believes it’s important to track and better understand asteroids overall.

“I don’t lie awake wondering about, you know, is a dinosaur-killer asteroid gonna come and destroy us all. We’ve got other things to worry about,” he said.

“It is something that I think that it’s prudent to begin to think about, measuring where or looking for where asteroids are, because sometimes they sneak up on us.”

He also said that he’s excited to have these observation systems in place, and also by plans to try to deflect any asteroid that might be on a collision course with Earth.

In particular, he noted NASA’s Double Asteroid Redirection Test (DART) mission to a two-asteroid system. The goal was to see if we could move an asteroid by slamming something into one.

The spacecraft crashed into one of the asteroids to see if doing so could change its orbit. It was deemed a success. And now the European Space Agency has a spacecraft on its way back to the system for more follow-up observations.

Asteroid to impact the moon?

Weigert and his team recently released a pre-print study about 2024 YR4, a newly discovered asteroid 60 metres in size that, at one point this year, raised some concerns about its chance that it would impact Earth in 2032.

But we’ve now been given the green light to stop worrying about that, as astronomers have refined the asteroid’s orbit somewhat, and it turns out that it won’t impact Earth.

However, there’s still a four per cent chance it will hit the moon.

In the new study from Weigert and his colleagues calculated what that might look like.

He said that typically, when an asteroid hits the moon or any planet without an atmosphere, it makes a crater about 10 times its own size. 

As for 2024 YR4, if it hits the moon, rocks and debris will blast out with most falling back down the the lunar surface. But some of those tiny rocks could make their way to Earth, the authors said.

“If it hits in the right spot, quite a bit of material could be delivered to Earth in the form of basically small lunar rocks, maybe centimetre-size or millimetre-size, perfect for making shooting stars, falling stars, and that would produce quite a wonderful meteor shower on Earth over several days, depending again and exactly where it strikes the moon,” Weigert said.

But, that would also pose a bit of a threat to satellites.

But Weigert anticipates that as the orbit is further refined — which won’t happen until 2028 the earliest, as its currently behind the sun — the chances of this happening will drop to zero.

Weigert also explained why it takes time to get a better estimate at the path of an asteroid.

“You can see it move across the sky very, very well, but it’s actually very, very difficult to tell how far away it is,” he said. 

“It’s only after watching it over a long period of time and knowing about the laws of physics and how gravity affects the orbit, that you can really refine it and say, ‘Okay, if it’s following the laws of physics, which it should be doing, that it’s traveling along this path.'”

When asked if he loses any sleep over the possibility of an asteroid hitting Earth, Weigert said quite simply, “No.”

“We’ve seen most of the really dangerous asteroids, and we’re continuing to work diligently to find as many more of the slightly less but still somewhat dangerous asteroids, and especially with something like the Rubin observatory coming online here, now that that task is going to sort of move to completion even faster than it has been.”