Athabasca University space scientist explains the cyclical nature of asteroid risk in light of 2024 YR4 asteroid
The Earth will likely avoid impact by the 2024 YR4 asteroid in 2032, according to the most recent calculations, but an Athabasca University space scientist says asteroid impacts are inevitable in the grand scheme of things.
That leaves the question: what’s going to hit us, and when? It turns out that’s not such an easy question to answer. Thousands of asteroids are tracked by scientists, mostly in the asteroid belt between Mars and Jupiter, but relatively few come into the inner solar system.
“If they cross Earth’s orbit, they can hit us,” explained Dr. Martin Connors, a professor in the Faculty of Science and Technology. “Earth actually has craters, and if you look up at the moon, it has tons of craters. Most of those are ancient, but many on Earth aren’t that ancient.”
Connors leads the Athabasca University Geophysical Observatory, located in AU’s home community of Athabasca, Alta. He said since Earth does get hit by asteroids, when it looks like there’s a possibility of an impact—such as the potential impact of the 2024 YR4 asteroid that was identified earlier this year—it tends to get a lot of attention.
The YR4 2024 asteroid, when observed in late January 2025, was projected to have roughly 3% chance to hit Earth in 2032. This prompted further analysis, and with more observations and calculations, the possibility of this asteroid hitting Earth in 2032 was revised to be near zero.
“It’s gotten a lot of attention,” he said. “That’s why the orbit has been defined much better, and the probability of it hitting has gone down.”
Identifying the risk and impact
As with all asteroids that periodically approach Earth’s orbit, it’s impossible to say with any certainty that 2024 YR4 won’t ever hit Earth.
“Mark Twain famously said it’s hard to make predictions, especially about the future,” Connors said. “That’s especially true of asteroids.”
The challenge with calculating an asteroid’s path with any degree of certainty is that there are just so many variables. Connors likened it to planning a 300 kilometre trip from Edmonton to Calgary, and trying to pinpoint the exact moment you’ll reach your destination.
“That’s about the precision that’s needed to project these things,” he said. “Tiny, tiny differences can make a big difference.”
Despite the relatively low chance for any asteroid to hit Earth, the sheer number of asteroids in the solar system increases the chances of impact, and those impacts can have significant effects on humans.
A 2013 meteor that entered the atmosphere near Chelyabinsk, Russia, shattered glass throughout the city and caused hundreds of injuries. One century before that, in 1908, the Tunguska event in a sparsely populated area of Siberia caused damage over an area of more than 2,000 square kilometres with the effects felt halfway around the world.
These asteroid impacts were significant events mainly due to their size. Many other smaller, less significant asteroid impacts occur relatively frequently.
Image of the asteroid 2024 YR4 taken by the European South Obsevatory's (ESO) Very Large Telescope (VLT). It shows a frame of the asteroid’s path through the night sky in January 2025, observed at infrared wavelengths with the HAWK-I instrument. These early observations contributed to increasing the odds of an impact on 22 December 2032 above 1%. However, thanks to newer data the odds have dropped to nearly zero. Credit: ESO/O. Hainaut
Many asteroids are periodic visitors
Connors said there are many asteroids in the solar system that are not likely to ever come anywhere near Earth, but other asteroids make regular appearances near Earth’s orbit, including 2024 YR4 and another type of asteroid he has studied extensively, called an Alinda asteroid.
These asteroids orbit of the sun every four years, caused by what’s called resonance with Jupiter, which orbits the sun every 12 years. He said Jupiter’s gravity effectively “pumps” the orbit of these periodic asteroids, keeping them in a four-year orbit in much the same way as many small pushes on a playground swing can propel the kid you’re pushing to greater heights.
“With these asteroids, it’s a little more complicated than a swing. They go around the sun three times for each time Jupiter goes around,” he said. “So, that means like, if you pushed the kid on the swing every third time, you’d still pump up their motion.”
Due to other factors, such as the angle of these asteroids’ orbits, astronomers tend to see this type of asteroid pass near Earth every four years for a few decades, before not seeing them near Earth for perhaps 100 years, before the orbits line up again to the point that it could be a risk to Earth.
The most realistic response, which has been done, is to catalogue them. We know that about 95% of the dangerous asteroids have been catalogued.
Dr. Martin Connors
Asteroids will hit Earth ... but when?
“These things will come back, and that’s the point,” Connors said. “And we can’t calculate such orbits 100 years in the future. There are too many unknown factors and all the (statistical) errors build up. You can’t say in the future with any certainty.”
Asteroid impacts are likely to continue on Earth, with varying sizes and intensities, but it’s exceedingly difficult to predict which asteroids may strike, when they may strike, and how significant the impact would be.
Preparation and monitoring of near-Earth-orbit asteroids, then, is an important way scientists can help us prepare for potential impacts.
“The most realistic response, which has been done, is to catalogue them,” Connors said. “We know that about 95% of the dangerous asteroids have been catalogued.”
The gaps in our knowledge, he explained, relate to objects that are within Earth’s orbit—closer to the sun than Earth. In these cases, the asteroids would only be visible in the sky during daylight hours, when even with telescopes, scientists can’t easily see them.
There are spacecraft that will be able to get better images of these types of asteroids, which will improve the cataloguing, but nonetheless the risk remains. A big one might not hit for 100 or even 10,000 years, which is a very small amount of time on an astronomical scale. It’s not something to lose much sleep over, but nonetheless preparation is important—and relatively inexpensive.
“For example, in 2027, the NASA Near-Earth Object Surveyor spacecraft will be launched to greatly increase our knowledge of the asteroid hazard,” Connors said. “Compared to potential losses, the cost of a spacecraft is quite low.”