YR4, a building-sized asteroid, was discovered in late 2024. It was predicted to hit Earth on December 22, 2032. Specifically, in February of this year, researchers calculated and found that the probability of impact peaked at 3.1% - the highest level ever recorded, making it the riskiest asteroid ever.
However, thanks to new observations from both the ground and space, scientists have determined the asteroid's exact orbit and size, thereby eliminating the risk of it hitting Earth.
According to NASA, data collected from the last observation in early June, just before YR4 disappeared from view, has improved the accuracy of predicting its location in the next 7 years by 20%.
However, even if Earth escapes, YR4 could still crash into the Moon in late 2032. This is a rare event in human history and it also creates new risks that we have to face.
The threat is not from direct collision.
Earth would not face significant danger if YR4 were to hit the Moon. But astronauts near the Moon, or human infrastructure present on the Moon’s surface at the time, could be affected. The same could be said of satellites orbiting Earth, which are essential to modern navigation, communications, and operations.
Even activities in low Earth orbit can be threatened by debris. This is especially true for structures like the International Space Station (ISS), which will be decommissioned and out of low Earth orbit well before the time of impact.
Once a prime example of the important role of planetary defense systems – detecting and tracking asteroids that could collide with Earth – YR4 could now redefine the scope of the field’s missions, including the threat to the Moon.
“We’re starting to realize that maybe we need to extend that shield a little bit further,” said Paul Wiegert, a professor of astronomy and physics at Western University in Ontario, Canada. “We’ve got things that need to be protected further away from Earth, and our vision needs to adapt.”
According to estimates from the James Webb Space Telescope in March, YR4 is about 60 meters in diameter – equivalent to a “city killer” (destroying an entire city) if it hits Earth. While not a “planet killer” like asteroids 1km or larger in size – the kind that can cause mass extinctions – YR4 is still capable of causing regional catastrophe if it hits.
With the potential to create a crater about 1km wide on the Moon's surface, the event is predicted to be the largest impact in the past 5,000 years. According to models by the research team led by Wiegert, the explosion could release about 100 million kg of lunar rocks and dust into space.
A piece of material just a few millimeters in size could hurtle toward Earth at extremely high speeds over a period of days to months, creating a spectacular meteor shower in the sky. However, Earth would be protected by its atmosphere and no one on the ground would need to worry about seeing such a meteor shower. The main danger lies in the possibility that small pieces of material could hit active satellites.
What can we do to reduce the damage?
A planetary defense scenario is often more obvious if we know an asteroid is headed straight for Earth. Take NASA’s DART mission in 2022, for example, when a spacecraft was sent to crash into the asteroid Dimorphos to test its ability to deflect it. The mission was successful, changing the target asteroid’s orbit.
However, the decision to launch a similar mission to prevent YR4 from hitting the Moon remains unclear. The decision will depend on risk assessments, when the object returns to the observation zone around 2028.
If the impact occurs without causing serious damage, it could create a rare opportunity to study how the lunar surface responds to large-scale impacts, something scientists have not seen in modern times.
What is worrying is that YR4 was only discovered by the ATLAS telescope in Chile about 2 days after it had passed by Earth at its closest distance. Before that, the celestial body was completely "invisible", hidden by the bright light from the Sun.
A similar situation occurred in 2013 in Chelyabinsk, Russia, when a meteorite suddenly exploded in the atmosphere and created a powerful shock wave, injuring more than 1,500 people.
Asteroids are challenging to detect and track, as they do not emit light of their own and are too small to be easily observed from a distance. Additionally, objects that fly in the direction of the Sun create large “blind spots” for ground-based telescopes.
However, hope is coming from future projects such as NASA's NEO Surveyor telescope (scheduled to launch in 2027) and the European Space Agency's (ESA) NEOMIR satellite, scheduled to launch in the early 2030s. These instruments will help detect objects near the Sun that were previously nearly invisible.
Meanwhile, the Vera C. Rubin Observatory in Chile – whose first images were released in June – has discovered more than 2,100 new asteroids in just seven nights of observations, including seven near-Earth objects. While none of these objects pose a threat, Rubin’s powerful detection capabilities combined with James Webb’s tracking capabilities will make for a strategic duo in protecting Earth and the Moon.
A proposal to use Webb to observe YR4 in the spring of 2026 has just been approved. This could be the last chance to observe the object before 2028.
“The observing program will give planners two valuable years – perhaps a sigh of relief – by having an 80% chance of ruling out a collision scenario,” de Wit said. “But it will also be a valuable practical lesson in preparing for other objects that Rubin may discover in the future.”
Source: https://www.vietnamplus.vn/moi-de-doa-ky-la-tu-mot-tieu-hanh-tinh-co-kha-nang-huy-diet-mat-trang-post1052107.vnp
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