Astronomers detected a 40-to-80-meter asteroid, dubbed a “city killer,” with the potential to collide with Earth in 2032, but Reynier Squillace is not worried.
Squillace is a second-year graduate student in the University of Virginia astronomy department who has written about asteroid defense. They said that despite NASA increasing the threat level from 1% to 2.3% and now back down to 1%, asteroid 2024 YR4, first sighted in December 2024, probably won’t strike the Earth. And, if it looks as if it might, there are steps to take.
“We don’t know all of the parameters in its orbit,” Squillace said. “These kinds of orbits are really complicated because they’re affected by a variety of different bodies, not just the sun, and they can start on really wonky orbits.”
Reynier Squillace, a graduate student who has written about planetary defense, thinks asteroid 2024 YR4 will not be a threat. (Photo by Matt Riley, University Communications)
As they continue to observe the asteroid, skywatchers will be able to better define its uncertain trajectory and how close it will pass to Earth to better refine its chances of striking the planet and its effects.
“This is not the first possible collider that we saw in 2024,” Squillace said. “Two months before YR4 was found, there was 2024 RW1, a minor asteroid found at the Catalina Sky Survey. And Jaqueline Fazekas, who was an observer for the Catalina Sky Survey, found it at around 10 p.m. Within three hours, the probability of impact jumped to 100% and by about 9 a.m. the next day, people had tracked down exactly when and where it would hit, which was Luzon in the Philippines at around noon that day. And they predicted that it would evaporate in the atmosphere, which it did.”
Squillace said the first step to tracking an asteroid is observation. A system of telescopes monitors near-Earth objects and sends the data to NASA, which calculates the likelihood of a collision. If the asteroid is on course to hit Earth and is too large to burn up in the atmosphere, there are methods that can used to change its trajectory.
“The larger you get in diameter, the actual threat goes up by the power of three, because the volume gets so much bigger,” Squillace said. “Once you get up to something such as 80 meters, we’re talking a serious threat that could actually destroy a city.”
But Squillace said there are layers of planetary defense, including deflection.
“Deflection has seen a huge amount of success in the last five years or so,” Squillace said. “I think the double asteroid redirection test was, in my opinion, the single greatest success of modern astronomy.”
NASA’s double-asteroid redirection test, launched in 2022, was an actual experiment in space. It sent a rocket to strike an asteroid named Dimorphos, orbiting a much larger asteroid named Didymos, a target at a distance equal to the size of a single atom held at arm’s length.
“It was tiny, and they managed to hit the thing with a rocket,” Squillace said. “Astronomers found that the orbit of Dimorphos had changed how it orbits Didymos. NASA did it around a double-asteroid because if you have a small orbital change, which is all that would be necessary to redirect an asteroid from the Earth, it’s much easier to notice if the orbit is quite small, such as around another asteroid.”
NASA’s double-asteroid redirection test sends a rocket to strike an asteroid orbiting a much larger asteroid, changing the smaller asteroid’s orbit. (NASA image)
Squillace said there have also been simulated experiments indicating that a nuclear blast could be deployed against an asteroid.
“The X rays from a nuclear blast can vaporize the surface of the asteroid into just gas, and because that gas is so heavy, when it expands against the asteroid, the asteroid is deflected,” Squillace said. “It’s not just the shock wave from a nuclear blast that could deflect an asteroid, but the X rays.”
The challenge is to keep the blast small enough to prevent the asteroid from being blown into pieces that would then shower down on the planet.
Still, if these defenses fail, the planet could take the hit.
“If it’s going to hit the Earth and it’s going to land somewhere that is not the ocean or a desert, the scale is a city destroyer,” Squillace said. “The absolute worst-case scenario is that you have to evacuate a city. It’s a bad scenario. The economic devastation would be terrible, but I’m from California. We’ve had to evacuate cities for natural disasters before, and unlike wildfires, this is one that we can predict to the exact minute and the exact mile.”
