It's certain that recently discovered asteroid 2024 YR4 will swing close to Earth in 2032. The chances of an impact remain low — but with relatively limited observations so far, the odds are in flux.
On Jan. 31, the collision impact probability was 1.4 percent. As of Feb. 7, NASA reports it's 2.3 percent, which also means a 97.7 percent chance of missing our humble blue world. But don't be surprised if that number climbs higher: It's normal for the impact odds to increase before falling or disappearing completely.
"It's not surprising the percentage went up," Bruce Betts, an astronomer and the chief scientist at The Planetary Society, an organization promoting space exploration, told Mashable.
"When you see the impact odds go up, it doesn't give you a good feeling," Betts added. "But there's much more likelihood that it's okay."
Asteroid 2024 YR4 — spotted by a telescope from the NASA-funded Asteroid Terrestrial-impact Last Alert System — has been deemed an object worthy of close monitoring because of its size. " Currently, no other known large asteroids have an impact probability above 1 percent," the space agency explained. It's between 130 to 300 feet wide, enough to be dubbed a "city-killer" asteroid — if it indeed hit a city. (For reference, the asteroid that hit Arizona 50,000 years ago and created the 600-foot-deep "Meteor Crater" was 100 to 170 feet, or 30 to 50 meters, across. "A similar-size impact event today could destroy a city the size of Kansas City," David Kring, an impact cratering expert at the Lunar and Planetary Institute, explained in a NASA blog.)
Telescopes will refine the asteroid's orbit around the solar system over the coming months, until it travels too far away to observe (it will return again in 2028). And this added information may likely, though temporarily, boost its Earth impact odds. That's because the asteroid's risk corridor or area of uncertainty around Earth will shrink as astronomers can better define its orbit. But as long as Earth remains in that estimated hazard area — like a catcher's mitt awaiting a high-speed baseball — its relative odds of getting hit increases as the possible range of uncertainty shrinks.
"Earth is taking up a bigger percentage of that uncertain area," Betts explained. "So the impact percentage goes up."
"This is a real threat. But it's not very common that it happens."
Yet space is vast. And at the same time the area of uncertainty is shrinking, more observations reveal and shift where exactly this zone of uncertainty is. The shrinking area typically moves off of Earth, meaning our planet is no longer in that potential impact area. This happened with the asteroid Apophis — a 1,100-foot-wide behemoth that once had a small chance of impacts in both 2029 and 2036. But more precise telescope observations moved Apophis' range of trajectory off of Earth. The impact probability then plummeted.
"It dropped to zero," Betts said.
"It’s a funny thing about homing in on an asteroid and calculating its path, future position, and probability of impacting Earth – it will often appear risky during initial observations, get riskier, and then suddenly become entirely safe," the European Space Agency noted.
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In the unlikely scenario that the large asteroid does hit Earth, such an event won't necessarily spell doom. Over 70 percent of the planet is covered in ocean, meaning there's a good chance of a relatively remote impact. And if it were headed to a populated region, you'd have plenty of notice. Space agencies like NASA and the European Space Agency, along with organizations like the International Asteroid Warning Network (IAWN), would vigilantly monitor the menacing object. If necessary, NASA would issue its first-ever asteroid warning. People could be evacuated from vulnerable regions.
In the future, with enough foresight, humanity could choose to launch a spacecraft that could impact such an asteroid, and nudge it off its Earth-bound course. NASA has already successfully achieved such an intentional impact during its unprecedented DART mission in 2022. But this was only a test on the non-threatening asteroid Dimorphos; it's not a ready-to-launch technology.
It remains unlikely that Earth and asteroid 2024 YR4 will be at the same place, at the same time, on December 22, 2032. But don't be alarmed if the impact odds go up.
"This is a real threat," said Betts. "But it's not very common that it happens."
The risks of an asteroid impact
Here are today's general risks from asteroids or comets both tiny and very large. Importantly, even relatively small rocks can still be threatening, as the surprise 56-foot (17-meter) rock that exploded over Russia and blew out people's windows in 2013 proved.
Every single day about 100 tons of dust and sand-sized particles fall through Earth's atmosphere and promptly burn up.
Every year, on average, an "automobile-sized asteroid" plummets through our sky and explodes, according to NASA.
Impacts by objects around 460 feet (140 meters wide) in diameter occur every 10,000 to 20,000 years.
A "dinosaur-killing" impact from a rock perhaps a half-mile across or larger happens on 100-million-year timescales.
