In recorded history, near-Earth asteroids, which briefly became the highest risk space object, have shifted astronomers’ attention to our moon.
The asteroid discovered in December last year in 2024 attracted global attention when calculations show that it had a 3% chance of hitting Earth in 2032, the highest probability of its size ever. After intensive tracking of observatories around the world, the risk of earth impact has dropped to less than 0.001%. But scientists now calculate a 4% chance that an asteroid could hit the moon.
“If asteroids affect the moon, the Earth’s system could be shadowed by particles that detach from the moon and asteroids and could threaten human space infrastructure and operations,” explains Professor Karri Muinonen of the University of Helsinki, whose team at the University of Helsinki has been tracking the forefront of space rocks.
Finnish astronomers have been closely following the asteroid since January 30, when the International Asteroid Warning Network issued the first notice about the object. Using the Canary Islands’ 2.5-meter Nordic optical telescope, the researchers played a crucial role in perfecting our understanding of asteroid trajectory.
“We have always focused on the precise position and motion of asteroids and analyzing their rotation, size and shape. This information is critical to better predicting the future trajectory of asteroids and ultimately refine their impact probability,” said Zuri Gray, a postdoctoral researcher at the University of Helsinki.
A key question continues until recently: How big is the 2024 YR4? The initial estimated diameter ranges from 40 meters to 90 meters. To obtain more precise measurements, scientists turned to the James Webb Space Telescope (JWST), which observed the asteroid on March 26. JWST has the only ability to measure thermal radiation from an asteroid and can directly indicate its size.
“The initial diameter estimate of an asteroid is limited to visible light measurements, depending on the size and reflectivity of the surface. However, the heat emission at infrared wavelengths is a direct indication of the magnitude.”
After careful analysis, the team determined that the asteroid’s range was about 60 meters (the error amplitude was 7 meters). This size determination helps assess the potential consequences of its impact on the moon and falls within the asteroid range, hitting Earth approximately every 5,000 years.
The success of tracking this object highlights the critical role of medium-sized telescopes in planetary defense.
“We are able to observe asteroids very quickly and refine their estimates. Flexible, high-quality, medium-sized astronomical facilities such as NOT are essential for fast follow-up of these potentially dangerous asteroids,” said Associate Professor Mikael Granvik of the University of Helsinki.
Observations in 2024 will last until April 2025 or May 2025, after which asteroids will not be able to be observed from Earth until the next approach in 2028. Meanwhile, space agencies and astronomers around the world are collecting data that will help determine whether lunar impacts will occur in 2032.
In Finland, the government’s responsibility for risk assessment of near-Earth objects is within the National Land Survey, and a new space situation awareness center is being established to monitor these and other space-related risks.
For now, our planet seems safer than this particular cosmic visitor, but our closest celestial neighbors may need to be prepared for the impact.
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