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Odds are a funny thing. 1-in-100, for example, sounds like a long shot—until you find out it’s the chance that an asteroid will impact Earth. In a surprising—but not definitive—turn of events, early warning systems this week found that an asteroid set to swing by Earth in 2032 has a 1-in-63 chance of smashing into our planet. Here’s what you need to know about the asteroid, its potential impacts, and why there’s no reason to panic. At least not yet.
What we know about asteroid 2024 YR4 NASA’s Asteroid Terrestrial-impact Last Alert System (ATLAS) in Chile first spotted the asteroid on December 27, 2024. ATLAS promptly reported the asteroid to the Minor Planet Center, a clearing house for the positional measurements of small bodies like asteroids and comets.
The asteroid measures between 130 and 300 feet wide (40 to 90 meters), based on estimates from its reflected light. It’s currently moving away from Earth at 8.24 miles per second (13.26 kilometers per second).
According to NASA’s Center for Near-Earth Object Studies, 2024 YR4 could make impact on Earth six discrete times between 2032 and 2071, but the greatest likelihood is on December 22, 2032. The probability of 2024 YR4 hitting Earth decreases with each subsequent pass.
“It is moving away from the Sun, getting farther and farther and fainter and fainter,” said Paul Chodas, the Director of CNEOS, in a phone call with Gizmodo. “The key thing is that it’s fading. It requires larger and larger telescopes to detect, and by April we think it’ll be too faint to observe with the largest telescopes.”
According to a statement published Wednesday by the International Asteroid Warning Network, the impact risk corridor for the asteroid “extends across the eastern Pacific Ocean, northern South America, the Atlantic Ocean, Africa, the Arabian Sea, and South Asia.”
2024 YR4’s orbit relative to Earth and surrounding planets. Graphic: NASA/JPL Hazardous asteroids like 2024 YR4 are disturbingly common Asteroids are potentially hazardous by NASA’s standards if they are between 100 to 165 (30 to 50 meters) in diameter and their orbit of the Sun brings them within 5 million miles (8 million km) of our own orbit. But potentially hazardous asteroids (PHAs) rarely end up colliding with Earth. Depending on their size and incoming angle, asteroids can cause bright fireballs that explode and break apart in the atmosphere (called bolides, which can shatter windows) to gargantuan impact events that kill most life on Earth.
Material from space falls on Earth every day. Over the course of a year, about 5,200 tons (10,000 grand pianos) worth of space dust lands on the planet. But it’s imperceptible because of its size. The size of an asteroid is a critical reason for the amount of damage it causes on impact, and right now, scientists don’t have enough data to know the exact mass of 2024 YR4.
Many systems are monitoring NEOs, and all play a part in measuring the risk each object poses of entering Earth’s atmosphere and impacting. The Catalina Sky Survey and the Lincoln Near-Earth Asteroid Research (LINEAR) program are dedicated to the study of NEOs, including hazardous asteroids, but other telescopes and observatories also play important roles in spotting the objects. In 2023, a new algorithmic tool set to be deployed in the Vera Rubin Observatory’s 10-year survey of space and time found its first PHA, showing a promising new avenue for surveilling the worrying objects.
How asteroid impact probabilities are calculated The near-Earth ne’er-do-wells make up NASA’s Sentry Impact Risk Table, managed by CNEOS. The Sentry table is an automated monitoring system that constantly recalculates the impact possibilities of near-Earth asteroids over the course of the next 100 years.
2024 YR4 currently tops that running order of possible troublemakers by a significant margin. Its cumulative impact probability is currently 1-in-63, or a 1.58% chance of an impact (which, it should be stressed, means a 98.4% chance the asteroid misses Earth). In second position on Sentry’s table is 29075 (1950 DA), which is much less likely to hit Earth (the odds are 1-in-2,600), and such an impact is not expected until 2880.
Lucas Janson, a statistician at Harvard University, points out that pulling the ace of spades (or any card, for that matter) from a deck of cards is a 1-in-52 chance, or 1.92%. In other words, you’re more likely to pull an ace of spades from a deck than 2024 YR4 is to impact Earth. Janson offers another probability that’s even close to 2024 YR4’s 1.6% impact chance: There is a 1.56% chance of flipping a coin six times in a row and having it land on heads each time. Those odds are nearly the same as 2024 YR4 hitting Earth in 2032. Depending on how you frame it, such an event is either very unlikely or too likely for you to feel completely calm.
Asteroid impact probabilities have two main scales of measurement The CNEOS Sentry table automatically sorts asteroids by their cumulative hazard rating using the Palermo Technical Impact Hazard Scale. Developed by NEO specialists, this scale compares the likelihood of a potential impact to the average risk posed by objects of the same size or larger up to the predicted impact date. In other words, the Palermo scale tells scientists what the biggest issue on the table is at a given moment, by comparing a given asteroid’s threat to the danger posed by other space rocks like it.
The Palermo scale is not to be confused with the Torino Impact Hazard Scale, another way of measuring the danger posed by asteroids. The Torino Scale is more like the Moment Magnitude Scale for earthquakes or the Saffir-Simpson Scale for hurricanes—systems you might be familiar with; the Torino scale is a color-coded scale from 0 to 10 (white to red) indicating the severity of an asteroid threat.
2024 YR4 is a 3 on the Torino scale, meaning that the close encounter with the asteroid is “meriting attention by astronomers,” according to CNEOS. Level 3 asteroids have a “1% or greater chance of collision capable of localized destruction,” CNEOS notes, though, “Most likely, new telescopic observations will lead to re-assignment to Level 0.” To make it into the Threatening, or Orange, zone of the Torino scale, 2024 YR4 would need to attain level 5 status.
If you didn’t follow all that, don’t be disheartened. “Torino’s too simplified to satisfy people but Palermo is too complicated to communicate easily to a lot of the public,” said Bruce Betts, Chief Scientist at the Planetary Society, in a phone call with Gizmodo.
Betts added that the odds of impact tend to creep up before they drop to zero, as uncertainty in the asteroid’s path decreases. If uncertainty in the path decreases, but Earth remains in that slimmer range of potential trajectories, the impact probability rises. Then, as follow-up observations reduce the possible paths further, Earth (ideally and historically) falls out of the impact path, causing the impact probability to plummet towards zero. In fact, 2024 YR4 started out this week at 1-in-83 odds of an impact, which rose to 1-in-71 by midweek. Today, CNEOS’ Sentry updated that figure to 1-in-63. But this is par for the course in refining the asteroid’s potential path, and subsequent observations and modeling will be critical in determining whether Earth remains in the asteroid’s orbital path or not.
A 2024 YR4 impact would be very bad, but not cataclysmic 2024 YR4 is a large asteroid (though its mass range offers a lot of wiggle room), but an impact with Earth would not cause a global cataclysm similar to that induced by the 6-mile-wide (10 km) meteor that slammed into the planet 66 million years ago, ending the reign of dinosaurs. An impact would produce about 8 megatons of energy, comparable to the Tunguska blast of 1908, according to NASA. But that’s if the asteroid is on the smaller side of its mass range—if it’s about twice that size, it could expel nearly 300 megatons of energy and unleash catastrophic damage over a wide area.
CNEOS also maintains a handy resource of hypothetical impact scenarios that indicate how scientists could respond to asteroid threats of varying sizes, velocities, orbits, and differing amounts of warning. These CNEOS scenarios—which play out annually at the IAA Planetary Defense Conference—are important tests of humankind’s emergency preparedness in the face of an oncoming asteroid strike.
A graphic showing the damage caused by asteroids of different sizes. Graphic: NASA Other potentially hazardous asteroids are on the horizon Though 2024 YR4 suddenly popped up on astronomers’ radars as a possible threat, there are other asteroids on the list. On April 13, 2029—a Friday, by the way—the asteroid 99942 Apophis will swing by our planet at an uncomfortably close 20,000 miles (32,000 km). Apophis was discovered in 2004 and, at 1,100 feet wide (335 meters), is much larger than 2024 YR4. It is the only asteroid to have a higher rating on the Torino scale than 2024 YR4, which (temporarily) attained a class 4 rating in late 2004.
There was initial concern that Apophis could impact Earth in 2068, but NASA’s 2021 calculations indicated that the asteroid doesn’t pose a threat for at least a century. Now, Apophis’ rating on the Torino scale is a 0. The change is a reminder that more observations of asteroids with uncertain orbits is critical to determining their exact trajectories—a difference between a normal day on Earth and a disastrous one.
Thankfully, 2024 YR4 will safely pass Earth on December 17, 2028, giving scientists a chance to observe it in greater detail. This flyby could help refine estimates of its mass, density, physical characteristics, orbital trajectory, and other key factors.
Scientists are working tirelessly to mitigate—and neutralize—threats from space Shortly after the Apophis odds were recalculated and near-Earth object researchers breathed a big sigh of relief, NASA scientists pulled off one of the most ambitious missions yet in spaceflight. It was the Double Asteroid Redirection Test, or DART, and it was the moment NASA scientists proved that humankind could change the trajectory of an asteroid. In other words, life on Earth may no longer be helpless in the face of potential destruction from space, as we’re on the verge of having the capability to nudge asteroids off course.
Ejecta streaming from Dimorphos about a day after the DART impact. Image: NASA, ESA, STScI, J. Li (PSI) “This is the one large-scale natural disaster that we can actually prevent,” Betts added. “The first thing you need to do is exactly what happened with this discovery—you need to find them.”
Over the next few months, ESA is coordinating observations of the asteroid with more powerful telescopes, including the European Southern Observatory’s Very Large Telescope. Betts noted that now that researchers have identified 2024 YR4, historical data on the object might help refine its orbital path (it’s a “chicken-or-egg” situation, Betts said).
Chodas told Gizmodo that space-based infrared observations would be ideal for observing the asteroid, but it’s difficult to justify using the Webb Space Telescope’s valuable observing time on the rock when scientists are still in the early stages of data collection and its impact probability remains relatively low.
“We often get asked, ‘Are you worried?’” Chodas said. “With a 99% chance that this asteroid will miss, no. The community is not worried, but we must pay attention to it. Because even though 1% is very small, the asteroid is of a size that it could cause serious damage.”
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