Key Takeaway:
A new asteroid, 2024 YR4, was detected in Chile at the end of 2024, with a small yet notable chance of colliding with Earth in 2032. Initially, estimates suggested a 3.1% probability of impact, but as of February 2024, calculations by the European Space Agency’s Near Earth Object Centre have revised this down to a 0.16% probability. This raises questions about why these predictions keep changing and how concerned should we be. Asteroids are fragments of rock, metal, or ice left over from the early days of the solar system, most of which reside in the asteroid belt between Mars and Jupiter. Space agencies like NASA and ESA actively monitor over 37,000 of these near-Earth asteroids (NEAs), with around 1,700 classified as having an elevated risk. Current models assume 2024 YR4 is spherical with a density typical of an S-type asteroid.
In the vast expanse of space, thousands of rocky bodies drift unnoticed, remnants of the solar system’s violent past. But every so often, one of these celestial wanderers captures the attention of astronomers—especially when it appears to be heading in our direction.
At the end of 2024, a new asteroid, named 2024 YR4, was detected streaking across the sky by astronomers in Chile. This 100-meter-wide space rock quickly made headlines, not just for its size but because it has a small yet notable chance of colliding with Earth in 2032. Initially, estimates suggested a 3.1% probability of impact—a figure that may not sound alarming until you realize it translates to a 1 in 32 chance.
As of February 2024, new calculations by the European Space Agency’s Near Earth Object Centre have revised this down to a 0.16% probability, or a 1 in 625 chance. While this represents a dramatic decrease in risk, it raises an important question: why do these predictions keep changing? And how concerned should we be?
A Collision Course? Understanding the Threat
Asteroids are fragments of rock, metal, or ice left over from the early days of the solar system, most of which reside in the asteroid belt between Mars and Jupiter. However, some stray close to Earth. Space agencies such as NASA and ESAactively monitor over 37,000 of these near-Earth asteroids (NEAs)—any celestial body that comes within 1.3 astronomical units (where one AU is the average distance between Earth and the Sun).
Out of these, around 1,700 are classified as having an elevated risk—meaning at some point in the future, they will make a relatively close approach to Earth. While the vast majority burn up harmlessly in the atmosphere, others can make it to the surface as meteorites, and in extremely rare cases, they can trigger catastrophic impacts.
Currently, around 44,000 kilograms of space debris hits Earth every year. Most of this consists of microscopic dust and tiny particles that produce the fleeting streaks of light we call shooting stars. But larger space rocks occasionally make their way to the surface, sometimes with explosive results.
One of the most notorious recent impacts occurred in 2013, when an 18-meter-wide asteroid exploded over Chelyabinsk, Russia. The event released a staggering 500 kilotons of energy, equivalent to 500,000 tonnes of TNT, shattering windows across multiple cities and injuring over 1,500 people.
By comparison, 2024 YR4 is significantly larger—estimated to be up to 100 meters in diameter. If such an object were to collide with Earth, it could release an energy equivalent to 7.8 megatons of TNT—15 times more powerful than the bomb dropped on Hiroshima. A direct impact on a major city could result in millions of casualties, while an ocean impact could trigger devastating tsunamis.
NASA has also suggested that 2024 YR4 has a small chance of hitting the Moon instead, which would pose no threat to Earth but would leave a significant impact crater on our celestial neighbor.
Why Do Impact Predictions Keep Changing?
Tracking asteroids is an incredibly complex task. Unlike stars and galaxies, asteroids do not emit light, making them notoriously difficult to detect. This is likely why 2024 YR4 remained undiscovered until late 2024.
Several factors affect an asteroid’s trajectory, and our current ability to track these variables comes with a degree of uncertainty. Some of the most important factors include:
- Albedo (Reflectivity): Asteroids that are more reflective receive greater radiation pressure from the Sun, which can subtly alter their paths. Conversely, darker asteroids absorb more heat, which can warm internal gases and cause tiny propulsion effects—nudging them onto a new trajectory.
- Shape and Rotation: Unlike planets, asteroids tend to be irregularly shaped. Their tumbling motion affects how solar radiation interacts with them, creating unpredictable forces.
- Gravitational Influences: Close encounters with other celestial bodies, including the Moon, can gravitationally deflect an asteroid’s path.
Current models assume 2024 YR4 is spherical with a density typical of an S-type asteroid (one of the most common types). However, this is likely an oversimplification. Future observations, possibly involving the James Webb Space Telescope (JWST), aim to refine our understanding of its size, shape, and composition.
Lessons from Past Space Predictions
Astronomers have encountered similar uncertainties with past space objects. When Comet 67P was first observed using Hubble, early predictions about its shape and trajectory turned out to be wildly inaccurate once the Rosetta spacecraftfinally provided close-up images. This demonstrates the limitations of long-range predictions and suggests that YR4’s current trajectory estimates may still change.
Can We Stop an Asteroid Impact?
The seven-year window between now and 2032 is narrow but not impossible for action. If 2024 YR4’s impact probability increases, scientists may consider using a planetary defense strategy.
In 2022, NASA’s DART mission successfully altered the orbit of the small asteroid Dimorphos by deliberately crashing a spacecraft into it. A similar deflection attempt could be made with 2024 YR4 if necessary.
However, other mitigation strategies, such as detonating a nuclear device near the asteroid, remain highly controversial. A nuclear explosion could accidentally shatter the asteroid into multiple fragments, potentially creating an even bigger threat as several smaller pieces rain down on different locations.
How Likely is a 2024 YR4 Impact?
Given how dynamic asteroid orbits are, there is a strong possibility that YR4 will be nudged off course before it ever becomes a real threat. The vast majority of Earth is uninhabited, making the chances of a direct impact on a major city relatively low. If necessary, evacuation plans could mitigate the potential loss of life.
For now, the best course of action is to keep tracking the asteroid. More observations will allow scientists to refine trajectory estimates, leading to more accurate impact probability calculations. As we’ve already seen, the odds can change significantly with new data.
While it’s not time to panic, 2024 YR4 serves as a reminder that Earth is not immune to cosmic hazards. With continued research and advancements in asteroid tracking technology, we may one day be able to predict and preventsuch threats with absolute certainty.
