An asteroid has a 2% chance of hitting Earth in 2032. Here's how astronomers are tracking it

CNN

15-02-2025

A recently discovered asteroid, named 2024 YR4, has on average a 2% chance of hitting Earth in 2032. While those odds of an impact are slim, astronomers are closely tracking the space rock to uncover more details — a process that could soon involve the most powerful observatory ever launched into space.
Not much is known about 2024 YR4, but the asteroid is estimated to be 131 to 295 feet (40 to 90 meters) wide, a 'size range comparable to that of a large building,' said Dr. Paul Chodas, manager for the Center for Near-Earth Object Studies, or CNEOS, at NASA's Jet Propulsion Laboratory in Pasadena, California.
That's not even close to the size of the 'planet-killer' asteroid that slammed into Earth 66 million years ago and led to the extinction of dinosaurs. That one was estimated to be about 6.2 miles (10 kilometers) in diameter and marked the last known large asteroid to hit our world. Planet killer asteroids are space rocks that are 1 kilometer across or larger and could have a devastating effect on life.
But smaller asteroids can cause regional devastation if they are determined to be on a collision course with Earth, which is why astronomers need to find out as much as possible — as soon as possible — about 2024 YR4.
Acquiring more data, like refining the space rock's trajectory, may reduce the odds of a direct hit to zero. But astronomers only have a certain amount of time to observe the asteroid before it fades from view in April. Now, they're planning to turn the powerful eye of the James Webb Space Telescope in 2024 YR4's direction with the hopes of pinning down the space rock's size and orbit.
Tracking a potentially hazardous space rock
The Asteroid Terrestrial-impact Last Alert System, or ATLAS, telescope in Rio Hurtado, Chile, first discovered 2024 YR4 on December 27. The telescope is one of the asteroid discovery programs funded by NASA to scan the sky in search of near-Earth asteroids, said Davide Farnocchia, navigation engineer at JPL and CNEOS, via email.
The size estimate of the asteroid has changed very little since then, despite multiple observations using an array of telescopes, because the space rock can only be studied using the amount of sunlight it reflects. The amount of light reflected by the asteroid's surface is used to estimate how big it is.
However, the Webb telescope, slated to begin observations of 2024 YR4 in early March, sees the universe in infrared light. Webb will be able to measure the heat reflected by the asteroid and provide a much more accurate size estimate, according to a Nature study published in December.
Since early January, astronomers have used the Magdalena Ridge Observatory in New Mexico, the Danish Telescope and the Very Large Telescope in Chile to track the asteroid, which is currently more than 30 million miles (48 million kilometers) from Earth and moving farther away over time, Farnocchia said. The celestial object should be visible through early April and disappear as it continues its orbit around the sun.
Observatories in Hawaii are also actively tracking the asteroid. The Panoramic Survey Telescope and Rapid Response System, or Pan-STARRS, located on the Haleakalā volcano in Maui, is the world's leading near-Earth object discovery telescope. Capable of spotting asteroids when they're distant from Earth, Pan-STARRS is currently part of the effort to follow 2024 YR4's movements.
'Hawaiʻi's telescopes are some of the most important tools for planetary defense,' said Doug Simons, director at the University of Hawaii's Institute for Astronomy, in a statement. 'Thanks to our prime location and advanced technology, we can spot, track, and study asteroids with incredible accuracy. That gives scientists the time they need to evaluate potential threats and figure out the best ways to respond.'
Webb will still be able to observe 2024 YR4 once the asteroid is beyond the viewing capabilities of Earth-based telescopes, providing measurements of the asteroid's position, according to the European Space Agency. After the initial observations in March, a second observation campaign has been planned for May. Scientists will use that data to provide the final measurements of the asteroid's orbit, as well as how its temperature has changed as it moves farther from the sun.
If 2024 YR4 disappears from view before space agencies can rule out any chance of impact, the space rock will remain on the risk list until it is back in view in June 2028. Current estimates of the asteroid's orbit suggest it returns to Earth's vicinity every four years, but it won't pose a threat in 2028, according to the University of Hawaii.
Estimating the risks
Understanding the exact size of the asteroid can help astronomers to estimate the risks if 2024 YR4 is determined to be on a future collision course with Earth.
'If the asteroid turns out to be on the large end of its estimated size range, the impact could produce blast damage as far as 50 kilometers (31 miles) from the impact site,' Chodas said. 'But that's in the unlikely event that it might impact at all. The potential for damage arises because of the incredibly high speed (about 17 kilometers per second, or 38,028 miles per hour) at which the asteroid would enter the atmosphere.'
Asteroids of this size impact Earth every few thousand years, and they can cause severe damage to local regions, according to the ESA.
In 1908, a 30-meter-wide (98-foot-wide) asteroid struck the Podkamennaya Tunguska River in a remote Siberian forest of Russia, according to the Planetary Society. The event leveled trees and destroyed forests across 830 square miles (2,150 square kilometers).
And in 2013, a 20-meter-wide (66-foot-wide) asteroid entered Earth's atmosphere over Chelyabinsk, Russia. It exploded in the air, releasing 20 to 30 times more energy than that of the first atomic bomb, generating brightness greater than the sun, exuding heat, damaging more than 7,000 buildings and injuring more than 1,000 people.
But if 2024 YR4 is on the larger end, the effects could be significantly worse, according to the ESA.
'If the asteroid is found to have a diameter in the (50 meter) range, and if it can be confirmed that it is a rocky asteroid, the effects would be similar to those of the Tunguska impact in 1908, where a surface area of (2,000 square kilometers) was devastated and 20 million trees were affected,' according to a document shared by the agency. 'This is equivalent to the area of a circle (25 kilometers) in diameter. If larger, the effects would extend to several tens of (kilometers).'
About 3,000 new near-Earth objects are found each year, but it's been more difficult to find asteroids within the size range of 2024 YR4 because they're dark, smaller and harder to spot with telescopes. Scientists estimate that there are about 600,000 rocky objects similar in size to the asteroid, but only about 2%, or 12,000, have been found, according to the ESA.
'Tiny asteroids do hit the Earth all the time, disintegrating in the atmosphere as fireballs; fortunately small ones cause little damage on the ground,' said Larry Denneau, an astronomer at University of Hawaii's Institute for Astronomy and coprincipal investigator at the ATLAS telescope, in a statement. 'Larger asteroids can cause much more damage, but they impact the Earth much less frequently. There are still many large ones out there that we haven't found yet, which is why we are continuously monitoring the whole sky to ensure that we stay ahead of potential threats.'