How Astronomers Predict Potential Earth-Crossing Asteroid Collisions
The detection of the asteroid 2024 YR4, with an initial impact probability that aroused severe worries in early 2025, put the scientific community on high alert. That January, I was getting ready for an early-morning lecture when I got a message saying that this asteroid had an unexpectedly high probability of hitting Earth.
My field of research revolves around monitoring celestial hazards; therefore, I was immediately inundated with inquiries from peers and students. Everyone was curious about the actual nature of this possible danger. When scientists find a new asteroid that potentially comes near Earth, they begin a process of constant tracking and investigation.
Via The Daily Galaxy
The goal is to refine the asteroid’s projected path and determine whether it might pose a real danger. While early observations provide critical data, they do not offer definitive answers. Scientists must continue monitoring the object over time to reduce uncertainties and arrive at more accurate predictions. The story of 2024 YR4 offers a clear window into how this process works and why predictions change as more information becomes available.
Understanding the Numbers Behind a Threat
The asteroid 2024 YR4, estimated to be around 60 meters in diameter, is roughly the size of a 15-story building. When it was first observed in January 2025, the reported probability of it striking Earth exceeded 1 percent. While that might sound low, in the context of asteroid tracking, it is significant.
Via Mashable
A 1 percent impact probability indicates that the asteroid has a 1 in 100 chance of colliding with Earth in the future. Even while it is uncommon, this amount of risk is significant enough to demand careful consideration, especially for an item this size. Astronomers continued to monitor 2024 YR4 and revise its trajectory model in the days and weeks that followed.
At first, the risk seemed to rise. The likelihood of impact increased to 3.1 percent by February 18. However, that number fell to 1.5% the following day. By February 24, more information had lowered the collision probability to just 0.004 percent. Scientists currently estimate that the asteroid’s chance of hitting Earth is less than 0.0000081 percent as of mid-June.
Via SciTechDaily
Interestingly, as the Earth-impact probability decreased, the chances of the asteroid hitting the Moon began to rise. On February 24, the probability of a lunar collision climbed to 1.7 percent, and by April 2, it had reached 3.8 percent. Should the asteroid strike the Moon, some debris could be ejected toward Earth. However, most of this material would burn up in the atmosphere and pose no threat to human life.
How Astronomers Calculate Risk
There are several scientific steps involved in calculating the probability of an asteroid impacting Earth. Using telescopes and radar, astronomers first monitor the asteroid to determine its position and velocity. There is always some degree of uncertainty because of measuring limits, even though these observations aid in charting the object’s orbit. Instead of producing a single, conclusive route, this uncertainty produces a “cloud” of potential orbital pathways.
Via MasterClass
Once the object’s potential paths are mapped out, scientists calculate which of those paths intersect with Earth’s orbit. If even a small portion of the orbital projections result in a collision, the asteroid is considered a potential hazard. The percentage of paths that intersect with Earth determines the impact probability. This number can change over time as more data becomes available and uncertainties are reduced.
The technique of astrometry is particularly important in this process. Astrometry allows astronomers to determine the precise orbit of a near-Earth object, often within a few kilometers of accuracy. Still, this method requires extensive observational data collected over a period of time. With insufficient data, the orbital path includes a wider range of possibilities, represented by what scientists call an “error ellipse.”
Via Space
The wider this ellipse, the greater the range of possible outcomes. As observations continue, the error ellipse narrows, and the chance of mistakenly including Earth in a possible collision path decreases. This is exactly what happened with 2024 YR4. Early on, the wide error ellipse made Earth appear to be within its path. As the ellipse narrowed with more data, it became clear that Earth was not at risk.
A Current Case – The 2032 Collision Possibility
In February 2025, a new alert emerged. Scientists identified another near-Earth object, again designated 2024 YR4, that could potentially strike Earth in the year 2032. Current models estimate the probability of impact at 2.1 percent, or roughly 1 in 47. While this figure sounds concerning, astronomers expect that further refinements will ultimately reduce that probability to zero.
Via MARCA
The likelihood of the asteroid striking the Moon instead is significantly lower. This scenario provides a chance to learn how astronomers find, categorize, and evaluate near-Earth objects. Near-Earth Objects (NEOs) are leftovers of the early solar system that are mostly made of rock, metal, or ice.
Larger NEOs can inflict significant harm if they strike Earth, as seen in the 2013 Chelyabinsk disaster, although the majority of them are harmless. Hundreds of people were hurt when that asteroid burst in the atmosphere over Russia, sending shockwaves through the atmosphere.
Via Business Daily
Observing and Identifying New Threats
Every night, observatories around the world conduct wide-field surveys of the night sky. These telescopes capture vast swaths of the sky, looking for things that move differently from stars. An object moving against the static background of stars is a good sign of an undetected asteroid.
The Asteroid Terrestrial Impact Last Alert System, or ATLAS, and the Catalina Sky Survey are two significant programs that support this endeavor. Four telescopes operated by ATLAS continually scan the sky, and the data is interpreted by computer systems. These algorithms help filter through hundreds of nightly observations to identify whether moving objects may be of interest.
Via LADbible
Catalina Sky Survey, with three telescopes, can image over half of the visible sky at a time and uses similar techniques to detect anomalies. Close NEOs appear to move faster than distant ones, just as a nearby train seems to speed by faster than one in the distance. Astronomers can determine an object’s proximity to Earth by measuring its movement.
Measuring Distance and Size
It is difficult to estimate an asteroid’s size and distance. Radio telescopes are more suited for measuring distance and fine-tuning size estimations, but optical telescopes are great for discovering new objects. To obtain accurate measurements, radar can reflect signals off the asteroid. Unfortunately, radar surveillance of 2024 YR4 is now not feasible because to its distance.
Via New Scientist
Asteroid composition, shape, and spin can also be inferred from brightness and variations in light over time. Size estimates are still unknown, though, because researchers do not yet know how reflective the asteroid is. Astronomers must put together various pieces of data, light curves, movement patterns, and orbital calculations to form an informed estimate of an asteroid’s size and trajectory.
Verifying a New Discovery
Astronomers use a database of known objects to compare newly discovered items. If it is confirmed as a new asteroid, follow-up observations are carried out to track its path more closely. These additional measurements help confirm whether the object is near Earth and what risk it might pose.
Via WCNC
There is a significant observational blind spot. Objects approaching Earth from the direction of the Sun are nearly impossible to detect with optical telescopes due to solar glare. This is how the Chelyabinsk meteor went unnoticed before it entered Earth’s atmosphere.
What Happens If an Impact Seems Likely
If an asteroid appears large enough and has at least a 1 percent chance of impacting Earth, it is reported to the International Asteroid Warning Network (IAWN). This network, established in 2013, coordinates global monitoring efforts and helps gather as much data as possible. 2024 YR4 triggered the first-ever Potential Asteroid Impact Notification issued by IAWN, signaling astronomers worldwide to intensify their observations.
Via The Wire
Even amateur astronomers contribute valuable data. Groups like the International Occultation Timing Association use specialized equipment to monitor how asteroids block light from distant stars, a method called occultation. These observations help determine an asteroid’s size and shape, adding to the body of data used in risk assessment.
Running Planetary Defense Exercises
To prepare for real-world threats, NASA organizes asteroid impact simulation exercises. In April 2024, nearly 100 experts from U.S. agencies and international organizations participated in a scenario developed by NASA’s Jet Propulsion Laboratory. In this simulation, a newly discovered asteroid had a 72 percent chance of striking Earth in 14 years.
Via Space
The projected impact zone included parts of North America, Southern Europe, and North Africa. But after several months of tracking, the asteroid moved too close to the Sun to observe further, adding to the uncertainty. These tabletop exercises help scientists and decision-makers understand how to respond, especially when vital data is temporarily unavailable.
Discover How Scientists Predict Asteroid Impact Risks
NASA is creating the Near Earth Object Surveyor (NEO Surveyor), an infrared space observatory scheduled for flight in late 2027, to address dangers sooner. Both light and dark asteroids, especially those in close orbit around the Sun, will be detected by it.
Via NDTV
The mission aims to improve early warning systems so that any necessary deflection missions can be planned years in advance. Astronomers depend on ongoing observations and international cooperation until such systems are completely functional.
Every new asteroid warning serves as a reminder of how much more people need to know and how important it is to continue being watchful. Similar to 2024 YR4, the majority of early threats prove to be innocuous. However, meticulous monitoring, measurement, and collaboration among the scientific community are the only ways to be certain.
