Asteroid 2024 YR4 has generated extraordinary excitement in the scientific community and public opinion since it was detected in late 2024. This object, whose orbit crosses Earth's path, has surpassed the 1% probability threshold of impact in 2032, which has been enough to trigger international defense protocols and multiply observations by the world's largest telescopes.
In this article, we'll break down everything we know about its physical characteristics, its discovery, the evolving probability of impact, monitoring and mitigation strategies, and the implications for planetary defense. We'll also analyze the potential consequences of a hypothetical impact and how international cooperation is helping to reduce the uncertainty surrounding this cosmic visitor.
Discovery of asteroid 2024 YR4 and initial studies
On December 27, 2024, the Asteroid Terrestrial-impact Last Alert System (ATLAS), from its station in Río Hurtado, Chile, first detected 2024 YR4. The discovery was immediately reported to the Minor Planet Center, triggering the international machinery for monitoring and tracking near-Earth objects (NEOs).
It was quickly determined that 2024 YR4 belongs to the group of Apollo-type asteroids, that is, those with orbits that cross that of our planet. Since its initial detection, the body has been the subject of intensive study using ground-based and space-based telescopes, such as the Very Large Telescope (VLT) in Chile, the Gran Telescopio Canarias, and the James Webb Space Telescope (JWST).
Initial data indicated an estimated size of between 40 and 90 meters, classifying it as an object capable of causing significant damage in the event of a regional impact. This size range was calculated from the absolute magnitude and assumed reflectivity (albedo), because direct observations are limited by the object's distance and low brightness.
In the days following its discovery, 2024 YR4 made a close approach to Earth of just over 828.000 kilometers (about 2,15 lunar distances) before beginning to move away. This data served to improve orbital calculations, although the asteroid soon became too faint for conventional telescopes, leaving hope for more sensitive instruments.
Physical characteristics: size, mass and composition
The most widely accepted size range for 2024 YR4 is between 40 and 90 meters in diameter, with optimistic estimates placing it at around 55 meters for a typical albedo of rocky asteroids. These values allow its size to be compared to that of the asteroid that generated the Tunguska event in 1908, or the one that formed the Barringer crater in Arizona 50.000 years ago.
The mass is estimated at around 220 million kilograms, assuming a typical density of 2,6 g/cm³, since everything points to it being a rocky S- or L-type asteroid. Preliminary spectroscopic analyses conducted with the Gran Telescopio Canarias and the Lowell Discovery Telescope support this hypothesis, revealing a composition based on silicates and metallic elements, with some iron and nickel content.
Another notable property is its rapid rotation: light curves obtained with the VLT and other telescopes indicate a rotation period of around 19,5 minutes, with a brightness variation of 0,42 magnitudes. This wobble is a symptom of an elongated and irregular shape, something common in asteroids of this size.
Neither mass nor density have been directly measured, although current estimates are precise enough to give an idea of the consequences of a possible impact. If it were to collide with Earth at a typical speed (about 17,3 km/s), it could release up to 7,7 megatonnes of energy, equivalent to 33 petajoules or about 500 times the energy of the Hiroshima bomb.
Orbit, trajectories and approaches to Earth
2024 YR4 describes an elliptical orbit around the Sun, with a semi-major axis of 2,54 astronomical units and a high eccentricity (0,66), which allows it to cross the path of the Earth. Its relative inclination to the ecliptic is low, just 3,45 degrees, and it completes a revolution around the Sun approximately every 4,05 years.
The perihelion, or closest point to the Sun, was reached on November 22, 2024, shortly before the first sighting, while the aphelion places it more than 4,2 astronomical units away. Apollo-type orbits, like YR4, are particularly closely watched for their ability to repeatedly intersect with Earth in different configurations over time.
The closest encounter to Earth before its discovery occurred on December 25, 2024, when it passed within 828.800 km of the planet. The next significant close approach is expected on December 17, 2028, when it will pass within approximately 7,9 million kilometers. This window will be crucial for observing it again and reducing the uncertainty surrounding its orbit ahead of the crucial 2032 meeting.
Currently, YR4 is tens of millions of kilometers away and rapidly receding, so only large-aperture telescopes or space-based instruments like the James Webb telescope will be able to track it until May 2025. From that date, the asteroid will remain out of visual range until 2028.
Evolution of impact probability and risk scales
Since the first days after the discovery, the probability of impact on December 22, 2032, has fluctuated as observations were added and orbital calculations were adjusted. Initially, the risk was estimated at 1,1%, which was quickly updated to 1,5% and at times reached figures close to 3% according to various sources (NASA, ESA, CNEOS).
These figures have placed 2024 YR4 at level 3 on the Turin scale, the second-highest score recorded since the asteroid Apophis reached level 2004 in 4 before being dismissed as a threat. A level 3 implies "an encounter with a possibility of impact worthy of special monitoring."
The Palermo scale, which combines risk and potential impact time, gives YR4 values of -3,08 (NASA), -3,44 (ESA) and -3,92 (NEODyS), which translates to a low risk in overall terms but sufficient to justify intensive monitoring.
International attention remains focused on risk assessment and maintaining response protocols for any changes in the trajectory. The experience with nearby objects such as the asteroid Apophis reinforces the importance of constant monitoring of these bodies.
In practical terms, a 98-99% probability suggests no impact, but the fact that the probability exceeds 1% has triggered all international alert and coordination mechanisms. The experience with Apophis 20 years ago calls for caution and prudence, maintaining active surveillance and preparation for any possible scenario.
International monitoring and planetary defense protocols
The reaction of the international community was not long in coming. NASA, the European Space Agency (ESA), and multiple private observatories have been involved in collecting data to improve orbit prediction. The Center for Near-Earth Object Studies (CNEOS) and the Jet Propulsion Laboratory (JPL) have been the mainstays in analyzing and updating the trajectory of 2024 YR4.
As the probability of impact exceeds 1%, the International Asteroid Early Warning Network (IAWN) has coordinated automatic protocols to notify the United Nations Office for Outer Space Affairs (UNOOSA) and the Space Mission Advisory Group (SMPAG). The latter is already discussing potential mitigation strategies, although for now, the probability of impact is expected to decrease with subsequent measurements.
The work does not stop: astronomers from all over the world aspire to make the most of the short visibility time of the asteroid, especially during the observing sessions granted to the James Webb Telescope in March and May. These observations seek not only to narrow down the orbit but also to determine its size and composition, key data for assessing the real risks.
The institutional levels (Turin and Palermo) dictate the actions to be followed, receiving specifications on when to report, when to activate alerts, and how to proceed in the event of a real threat.
What would happen in case of impact: scenarios and consequences
The size of 2024 YR4, although average in astronomical terms, keeps it far from being a threat of global extinction. However, if it hits, it could cause significant damage in specific regions.
The impact can occur in two main scenarios, depending on the composition and angle of entry:
- Atmospheric explosion (Tunguska type): If the object disintegrates in the atmosphere, the blast wave could devastate hundreds of square kilometers and cause material damage in nearby urban areas.
- Surface impact (Barringer crater type): If it manages to pass through the atmosphere, it can create a crater up to a kilometer in size and devastate areas several dozen kilometers away.
Recent estimates place the energy released upon impact at around 8 megatons of TNT, affecting areas near oceans, rural areas, and sparsely populated regions. The possibility of an ocean impact reduces the likelihood of large-scale tsunamis, but an impact on a populated area would require immediate evacuations.
A water impact could generate dangerous waves near the coast, but in general, inhabited areas would have some protection if the impact occurs in remote regions.
The role of large telescopes: the example of the James Webb
Due to the asteroid's rapid decline in brightness and its retreat, follow-up work relies on the use of telescopes like the James Webb telescope, which can observe in infrared and capture its heat. These observations will be key between March and May 2025, when precise data will still be possible.
JWST will allow direct measurement of the asteroid's size and improve the accuracy of its trajectory thanks to observations in various infrared and optical bands. The results will facilitate the updating of risk models and the planning of possible future actions.
Infrared detection also helps estimate its true size, as the heat it emits is proportional to its surface area and composition. The capabilities of these instruments will be vital in future observations, given that the object's magnitude already exceeds the limits of detectability with conventional ground-based telescopes.
Comparison with other famous asteroids: Apophis, Tunguska and Chelyabinsk
The case of 2024 YR4 has been compared on several occasions to that of the asteroid Apophis, which in 2004 raised concerns about a possible impact in 2029 until it was later ruled out. Apophis, measuring 375 meters, once reached level 4 on the Turin scale, while YR4, much smaller, remains at level 3 and presents a lower risk.
The 1908 Tunguska event, involving an object measuring 40 to 60 meters, left a crater of more than 2.000 km² in Siberia and served as a benchmark for the potential damage from atmospheric impacts. The Chelyabinsk meteor crash in 2013, measuring just 20 meters, caused thousands of injuries from broken glass in the Russian city, highlighting the danger of relatively small objects in urban areas.
These examples highlight the importance of monitoring systems and preparation for near-Earth objects of different sizes and characteristics.
Mitigation and Defense Measures: DART and Potential Diversion Missions
Given the potential risk, the international community has begun planning possible missions to deflect or alter the asteroid's trajectory. NASA's DART mission impacted the asteroid Dimorphos in 2022, demonstrating the viability of the strategy.
If observations in 2028 confirm a high risk, there would be a four-year window to design and launch a deflection mission, either through a kinetic impact or controlled explosives. International cooperation, including the UN and space agencies, ensures coordinated and transparent actions in any impact scenario.
In addition, the protocols include preventive evacuation and public information campaigns to minimize the social impact and avoid unfounded alarms.
The importance of scientific cooperation and accurate communication
The case of asteroid 2024 YR4 demonstrates the rapid and coordinated response capacity of the global scientific community. Transparency in measurements, constant risk updates, and collaboration between institutions have been essential to maintaining surveillance without generating unnecessary alarm.
These actions reinforce the idea that we now have greater tools to address space threats, and that international cooperation and effective communication are essential for proper management of these risks.
While the probability of impact continues to decrease with new observations, active monitoring and scientific collaboration keep humanity prepared to respond to any eventuality from the cosmos.
