Should you be worried about Asteroid 2024 YR4?

A recently discovered near-Earth asteroid, dubbed 2024 YR4, is making headlines because of the slim possibility that it could impact Earth on Dec. 22, 2032. Early observations suggest that it has about a 1% chance of colliding with our planet. So why all the fuss?

2024 YR4 is garnering so much attention because of more than 37,000 near-Earth asteroids already discovered, it is the only one with more than a 1 in 1,000 chance of impact. “It is rare to have an asteroid with a non-zero probability of hitting Earth,” said Heidi Hammel, Vice President for Science at the Association of Universities for Research in Astronomy and Vice President of the The Planetary Society’s board of directors.

To put it into context, 2024 YR4 has a Torino scale rating of as high as 3. The Torino Impact Hazard Scale ranges from 0 (no chance of impact) to 10 (certain impact likely to cause planetwide devastation). Ratings of 1 are fairly common among newly discovered asteroids, but follow-up observations have always reduced that rating to 0. Asteroid 2024 YR4’s rating of 3 is the second-highest an asteroid has ever reached. The only asteroid ranked higher was Apophis, discovered in 2004 and rated 4, but subsequently downgraded to 1 and then 0. We now know with certainty that Apophis will only pass close to Earth in 2029.

Right now, ESA estimates that 2024 YR4’s diameter is in the range of 40-100 meters (around 130-330 feet). If it did collide with Earth, an impactor of that size could cause an explosion in the atmosphere or even an impact crater, either of which could cause serious, even devastating, damage on the ground.

All of this means that 2024 YR4 merits significant attention from astronomers and public officials, which it’s getting.

“At this point,” said Hammel, “astronomers have measured the object’s orbit, and further observations will refine that orbit to give us a more precise understanding of its potential danger. We have a rough estimate of its size based on its brightness, and from variations in the brightness, we can infer that it has an elongated shape. Measurements at visible wavelengths suggest it may be a stony asteroid (S type).”

Hammel and her colleagues around the world will continue using space and ground-based telescopes to track the asteroid and refine predictions of its trajectory for as long as they can detect it. Astronomers are also combing through past data from periods when it may have been observable. 

“Both NASA and ESA have been involved in coordinated work, and there is also an International Asteroid Warning Network that facilitates shared information,” said Hammel. 

As more observations are obtained over longer periods of time, the uncertainty of where the asteroid will be when it comes near Earth in 2032 will get smaller. Odds are that the smaller uncertainty will cause the probability of impact to go to zero.

“Note that often, counterintuitively, the odds of impact go up before they drop to zero,” said Planetary Society Chief Scientist Bruce Betts. “This happened for Apophis and could happen for 2024 YR4. As more observations come in, the uncertainty in the area the asteroid will pass through decreases. But while that area still includes Earth, less uncertainty means the probability of impact increases.” This is usually temporary, as further observations shrink that area even more, eventually showing with high certainty that the asteroid will miss our planet. When this happens, the impact probability drops to zero. 

Although 2024 YR4’s potential for collision with Earth is serious and demands careful and extensive observation, it doesn’t mean anyone should panic.

“Your danger is far higher to have a car crash,” said Hammel, “so wear your seat belt!”